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MiniHawk-VTOL <a name="head-brief"></a>

The MiniHawk VTOL is a 3D-Printed Tricopter/Fixed-wing hybrid aircraft, capable of Vertical Take-off and Landing. As with its predecessor, the OrangeHawk VTOL, the MiniHawk is intended for R/C, FPV and UAV experimentation. Mechanical artwork, build instructions, and configuration settings are provided in this repository.

⚠️READ-ME - PROJECT STABILITY AND NEW VERSION⚠️ - 18 MARCH 2022: More than likely, you have stumbled on this project from a link on a YouTube video, such as How NOT to Flight Test a VTOL UAV or one of the other videos out there. If you want to try making this project, go for it! As of this writing, all the STL files on this repo, the Version 2.0 - Hotfix and 2.1 Preview zip file at the left of this text, and the most recent upload to the Hackaday.io page are "safe". Previously, the were some design flaws (the old tilt nacelle design), but these issues only exist for Version 2.0 STLs from prior to the 23 February Hotfix. Again, everything present on the master branch here should be safe to build and will not be altered for most of 2022.

Now, with that said, there is a new version coming out soon™, Version 2.1. However, at this point, this next version will not change any of the current STLs, so, again, you are totally safe to use the STLs, everything is working and flying great, and no changes to the aircraft design will be released until late this year or early next year. What the release of V2.1 will do is add some new bonus STLs/features, and otherwise it is just polishing presentation or rewriting documentation. I've been stuck in the prerelease of Version 2.1 for a few months, so some parts of this README are being rewritten, such as the build instructions and adding the Parts Tree Diagram and such. Here are my recommendations for building the project at this moment in time:

• Refer to the Development-Branch Build Instructions for the updated build instructions.
• Browse the Development-Branch Documentation Folder for all the new build instruction images; many of these are not yet added or used in the updated build instructions.
• Watch MiniHawk-VTOL Assembly in 100 Seconds to see the animated build steps.
• Cross-reference with the Older Build Instructions Below. You will see images and steps for the older Version 1.0 release, so ignore features that do not exist or have been redesigned in the intervening 1.5 years.

Sorry for the mess, I hope this helps. I enjoy promoting and polishing this project where I have time. Let me know if you have any questions, and have fun building! -Steve

Milestones

Project Page at Hackaday: HACKADAY.IO Page

MiniHawk Design Details and Features discussed here: RCGroups VTOLs Forum Thread

Featured MiniHawk-VTOL Builds by community members: RCGroups 3D-Printed Forum Thread

Accompanying Build Video Series: YouTube Playlist

Betaflight VTOL Firmware Build: vtol-motor-mix

Table of Contents

1. Introduction
   1.1 Description
   1.2 How To Use This Repo
   1.3 Remarks / FAQs
   1.4 Metrics
2. Build Information
   2.1 Recommended Tools
   2.2 Components and Electronics
   2.3 Airframe Parts Listing
3. Build Steps
   3.1 Part 1 - Airframe Structures
   3.2 Part 2 - Linkages and Servos
   3.3 Part 3 - Electronics and Finishing
4. Flight Testing
5. 3D Printing Guidelines
6. ArduPlane
   6.1 R/C Controls Configuration
   6.2 Flight Controller Connections
   6.3 Parameters
   6.4 Remarks
7. License

Description <a name="head-description"></a>

The MiniHawk is a 3D-Printed VTOL aircraft. It was designed with printability in mind, and is intended to provide the community with a common and accessible VTOL testbed for experimentation and tinkering. The vehicle uses three (3) brushless DC motors for propulsion, with the forward pair tilting for forward flight and yaw control, and the rear motor fixed for hover only. Four (4) servos are used to tilt the forward motors and to control the elevon control surfaces of the wing. The airframe is a "plank"-style wing with a center body containing avionics and battery, and internal conduits routing to the nacelles and servos. Twin vertical stabilizer fins provide mild directional stability.

How To Use This Repo <a name="head-usage"></a>

This project is hosted on GitHub, which is traditionally a software repository site, but the format works well for a hardware project such as the MiniHawk-VTOL, where a few of the features come in handy:

• The history for each part file is accessible; if you need an old version, it is available even off-line if you've "cloned" the repo. (Beware, cloning the repo means hundreds of MB download.)
• Versions and Releases are published just like a software project, and this includes setting milestones and planning future releases, keeping the community informed about what is next. Releases are the condensed set of essential files, placed in a zip archive, which represent a snapshot of the project at a moment when the artwork is stable and worth broad public distribution.
• The Issues tab allow for the community to participate in the evolution of the design by providing feedback or contributions toward improving the design.
• The Discussions tab is another location for communication on the project.

While I have described the hosting environment, it isn't necessary for you to make a GitHub account or participate in the project; and more than likely, you are just interested in downloading the STLs and making the plane. Here is what you need to do:

• Click on the Latest Release in the Top-Right section of this webpage. This will take you to the most recent version of the design that was stable.
• Read the description to understand what is new or notable for the release, and then look under the Assets section and find the .zip file named MiniHawk-VTOL-x.x.x.zip, where the 'x''s are the release version numbers. Skip the Source Code downloads as these are auto-generated by GitHub and represent the entire contents of the project, which you probably are not interested in unless you really want all of it.
• Unzip the archive and examine the files. A snapshot of this README you are reading is contained in the README.md file, and it should be able to be opened by any text editor.
• Follow the Build Steps below. It should be possible to print this page or save as a PDF. If you are code-savvy, this is all written in Markdown and should render in whatever text editor or Markdown renderer you prefer.

Remarks / FAQs <a name="head-faqs"></a>

• As this is a totally 3D-printed airframe, the fully-finished vehicle is moderately heavy, which is a handicap, especially in the hovering mode of flight. As such, be gentle and cautious in adding any additional weight. For the recommended print settings with a 0.4mm nozzle on standard PLA, the airframe alone weights a bit over 460g, and the all-up-weight of the finished vehicle is between 1000g to 1200g.
• The parts used in this project are commonly available in the drone racing and R/C plane market(s). Standard motors such as 2207, 2306 or similar can be used. The nacelle design dictates a maximum motor bell diameter of 29mm, but this is relaxed compared to previous versions of the design that had more stringent requirements. The Ball-Stud Linkage is perhaps the most specific part used, with Dubro #181, Dubro #190, or even Dubro #367 as acceptable options.
• The aerodynamics and stability of the vehicle are still under analysis and subject to revision. The CFD poses/cases used for aerodynamics analysis are included for independent study.
• As of Version 2 of this design, project files are prefixed with "MH7", as this is the 7th internal revision of the design of the MiniHawk VTOL. There may be some old "MH5" parts are retained in the repo; these are from the old version(s). Also, the "MH#" prefix is incidental and not to be confused with the MH airfoil series, of which the MH45 is used for this vehicle. Generally, "MiniHawk-VTOL" is the correct name for this design and any revisions to be released.
• This vehicle was designed in Autodesk Inventor Professional 2019. While compiled STLs are provided as open-access, the Solid Model and Assembly Source files for this vehicle are withheld at the time of this writing; contact me for inquires on obtaining a copy or further development. One minor accommodation: STEP/STP versions of some parts such as the Hatch/Lid are included for community derivations.
• There are some variants to each part, such as versions of the nose with and without NACA vents. The Winglet is available as "normal" or with an excavation for a GPS or other devices. The Hatch/Lid has a FPV Variant, which supports the Foxeer -Nano camera formfactor (15mm width) and has a 30.5mm grid for a video transmitter, such as the AKK Infinite DVR. All the part options and variations are detailed below in the Parts Tree Diagram.

Metrics <a name="head-metrics"></a>

MiniHawk Build Parts List and Tools <a name="build-brief"></a>

Recommended Tools and Equipment <a name="build-tools"></a>

• FDM/FFF 3D Printer with build volume greater than 23.1x210.7x150mm (A build height of 330mm or greater will allow for printing the nose and wings as single parts rather than split.)
• Soldering Station and associated tools and materials for electronics crafting
• Handcrafting Tools: Pliers, Side-Cut Diagonal Cutters, Sandpaper, Hobby Knife/Scalpel, Hand Drill, etc
• Adhesives and Consumables: Cyanoacrylate Glue, Hot-Melt Adhesive Gun, Tape

Components and Electronics <a name="build-components"></a>

Note 1: Front motors should be no larger than OutsideDiameter=29mm, able to produce between 500g to 800g static thrust (@full-throttle), and pitch speed of ~20m/s (@half-throttle) with 5-inch prop.
Note 2: Tail motor may be up to OutsideDiameter=30mm or more, able to produce between 700g to 1000g static thrust (@full-throttle) with up to a 6-inch prop.
Note 3: Servo bays are designed for up to 26mm wide servos, 17.5mm from bottom of mounting tabs to bottom of servo, 32mm from top of output shaft to bottom of servo, 12mm thick. Should fit most "Sub-Micro" Servos.
Note 4: Same pocket dimensions as above, but these are going to be fantastically abused and must be fairly tough. Or just count on stripping your non-metal-gear servos a lot.
Note 5: Can be omitted, but 3D-printed living-hinge on elevons will eventually fail, mend appropriately. Dubro #118 is 6 per package, Dubro #119 for 15/pkg.
Note 6: Alternatively, cut the servo cables and solder in-line extensions for the cables to reach to the flight controller, plus some slack.
Note 7: The clevises and rods can be purchased as a set, such as Du-Bro #185, which is a set of 5 rods with clevises already attached.
Note 8: The Ball Link thread size should be 1/16-inch / 62.5mil / 1.59mm. A more popular variant of this type of part has a 2-56 (86mil) thread size ball, which a bit large but should be adaptable to the nacelle motor tilt mount part. If you can only order metric hardware, 2mm thread size should be fine. Note that this is the ball-link-stud thread size; the ball-link-stud attaches to the ball-link-socket/coupler that captures a threaded rod, which then links to the servo arm. This linkage rod which goes between the servo arm and the ball-link-socket/coupler can be any size, but is assumed to be 2-56 here. Note 9: Diameter=[1.83mm to 1.87mm], formed from spare pieces of 2-56 Servo Pushrod. Use non-threaded smooth rod, roughen/knurl only one end slightly for press-fitting to nacelle.

Airframe Parts <a name="build-airframeparts"></a>

MiniHawk-VTOL Version 2.1 Aircraft
|-- Fuselage/Body  
|   |-- Empennage/Tail
|   |   |-- Print Option 1: As a Single Part - No Split, but layers are not aligned for max. strength
|   |   |   |-- MH7_Empennage-Full.stl
|   |   |
|   |   |-- Print Option 2: Split into Two Parts with print layers aligned for strength
|   |       |-- Print Option 2a: Explicit Print Supports
|   |       |   |-- MH7_Empennage-PrintSupports.stl
|   |       |
|   |       |-- Print Option 2b: No Explicit Print Supports, plain part
|   |           |-- MH7_Empennage.stl
|   |
|   |-- Nose
|   |   |-- Print Option 1: Full Nose - No Split
|   |   |   |-- MH7_Nose.stl
|   |   |
|   |   |-- Print Option 2: Nose in Two Pieces
|   |       |-- MH7_Nose_A.stl
|   |       |-- MH7_Nose_B.stl
|   |
|   |-- Avionics (Flight Controller) Tray
|   |   |-- Part Variant: Solid Tray, No Vibration Dampening
|   |   |   |-- MH7_AvionicsTray.stl
|   |   |
|   |   |-- Part Variant: Leaf-Spring Compliant-Mechanism Vibration-Dampening Version
|   |       |-- MH7_AvionicsTray2.stl
|   |
|   |-- Battery Tray
|       |-- MH7_BatteryTray.stl
|
|-- Hatch/Lid
|   |-- Part Variant: FPV 16mm-sized Camera and VTx Support
|   |   |-- Print Option 1: Long-axis Symmetric Half (TODO: Needs to be restored to -Full)
|   |   |   |-- MH7_Hatch-FPV-16mm.stl
|   |   |
|   |   |-- Print Option 2: Split into Two Parts for nicer print
|   |       |-- MH7_Hatch-FPV-16mm_a.stl
|   |       |-- MH7_Hatch-FPV-16mm_b.stl
|   |
|   |-- Part Variant: Vented with NACA Duct
|   |   |-- Print Option 1: Entire thing, split it yourself
|   |   |   |-- MH7_Hatch-Vented.stl
|   |   |
|   |   |-- Print Option 2: Split into Two Parts for nicer print
|   |       |-- MH7_Hatch-Vented_a.stl
|   |       |-- MH7_Hatch-Vented_b.stl
|   |
|   |-- Locking Latch Mechanism
|       |-- MH7_Hatch_LockingLatch.stl
|       |-- 1.85mm Steel Pin, Length=30mm
|
|-- Left Wing  
|   |-- Part Variant: Plain Wing
|   |   |-- Print Option 1: Entire wing
|   |   |   |-- MH7_WingLeft.stl
|   |   |
|   |   |-- Print Option 2: Split into Two Parts for smaller printers
|   |       |-- MH7_WingLeft_A.stl
|   |       |-- MH7_WingLeft_B.stl
|   |
|   |-- Part Variant: Solar Wing
|   |   |-- Print Option 1: Entire wing
|   |   |   |-- MH7_WingLeft-Solar.stl
|   |   |
|   |   |-- Print Option 2: Split into Two Parts for smaller printers
|   |       |-- MH7_WingLeft_A.stl
|   |       |-- MH7_WingLeft_B.stl
|   |
|   |-- Elevon Control Horn
|       |-- MH7_ControlHorn.stl
|
|-- Left Fin  
|   |-- MH7_FinLeft_Lower.stl  
|   |-- MH7_FinLeft_Upper.stl  
|
|-- Left Nacelle
|   |-- Part Variant: Ball Bearing Version
|   |   |-- MH7_Nacelle_A-Bearing.stl
|   |   |-- MH7_Nacelle_B-Bearing.stl
|   |
|   |-- Part Variant: Non-Ball Bearing Version
|   |   |-- MH7_Nacelle_A-NoBearing.stl
|   |   |-- MH7_Nacelle_B-NoBearing.stl
|   |
|   |-- Motor Tilt-Mount
|       |-- Part Variant: Ball Bearing Version
|       |   |-- MH7_TiltMount_A-Bearing.stl
|       |   |-- 3mm Shaft or Threaded Bolt, Length=44mm
|       |
|       |-- Part Variant: Non-Ball Bearing Version
|       |   |-- MH7_TiltMount_A-NoBearing.stl
|       |   |-- 1.85mm Steel Pin, Length=40mm
|       |
|       |-- MH7_TiltMount_B.stl
|       |-- BLDC Motor
|    
|-- Left Winglet
|   |-- Part Variant: Plain Winglet
|   |   |-- MH7_WingletLeft.stl
|   |
|   |-- Part Variant: GPS Pocket
|       |-- MH7_WingletLeft-GPS.stl
|
|-- Right {Wing, Fin, Nacelle, Motor Tilt-Mount, Winglet} 
|   |-- For each of the symmetric parts, to create the right-side version, simply mirror the part in your slicer software. 
        Be _very careful_ please! Be sure you understand how all the parts go together, particularly the Nacelle pieces: 
        The nacelle _A piece is always near the aircraft center body, with the _B piece on the outboard side, aligned with 
        the servos and away from the center body. You should print four unique Nacelle pieces, with no two alike: 
        Two non-mirrored pieces of _A and _B, and two mirrored pieces of _A and _B.

Supporting Devices and Parts
|-- Weight & Balance Jackpoint Stand
|   |-- Nacelle-Support Beam
|   |   |-- MH7_WeightBalanceStand_Beam.stl
|   |   |-- MH7_WeightBalanceStand_Support.stl
|   |   |-- Two 1.85mm Steel Pins, Length=50mm each
|   |
|   |-- Empennage-Support Jack
|       |-- MH7_WeightBalanceStand_Foot.stl
|       |-- MH7_WeightBalanceStand_Support.stl (After gluing, bend the legs with hot water to form a triangle stance)
|       |-- 1.85mm Steel Pin, Length=50mm
|
|-- STEP/STP Version of the Hatch/Lid for Community Mods
    |-- MH7_Hatch_RELEASED.stp

Build Sequence <a name="buildseq-brief"></a>

The following instructions assume that a full set of airframe parts have been printed, as enumerated above. Refer to the 3D Printing Guidelines Section for details on the typical slicer settings for each part. Also, 3MF production files are available in the 3mf-Implementations repo folder, but whether the print settings properly transfer to your particular printer is a bit of a gamble.

Part 1 - Airframe Structures and Motor Mount/Tilt Attachment <a name="buildseq-part1"></a>

1. Clean all 3D-Printed parts, remove all brim/support material. Remove any burrs or blemishes. For each wing, carefully carve away any stringing or over-extrusion in the hinge reinforcement wells such that the hinge pin will fit. Figure-1 The pitot-probe shaft and other small features may also have stringing that should be removed.

2. Carefully cut the elevons free if needed (WARNING! Only cut slots on either end to allow for surface deflection, DO NOT cut the entire elevon out). Figure-2 Gently exercise each surface up and down until the living hinge is established. The best way to start is to bend the elevons downward (as if pitching nose down) with a solid planar object to distribute the pressure on the control surface evenly. Only go as far as you feel comfortable, and then reverse direction. Continue to exercise the hinge gently until it is moving +/- 30 degrees. If you printed with PLA or another work-hardening material, don't continue cycling the hinge until the reenforcement tape or tabs are installed; only then should the hinge be further broken-in until it has smooth movement.

3. Bond the Canopy/Hatch-Lid pieces together using Thin/Medium Cyanoacrylate and set aside to cure. Figure-3

4. Bond the Empennage Halves together using Cyanoacrylate. (Skip this step if you printed the -Full one-piece version.) Set aside to cure. Figure-4

5. Press-fit the Control Horn pieces into the elevons to test the fit. The Control Horn is inserted from the top, protruding through the elevon with the hole centered below the hingeline, inline with the elevon servo linkage. The pieces should be fairly flush on the Elevon Top Surface, with approximately 0.5mm extending above the surface. The fit should be tight, but do not force the control horn too hard or you may split print layers and cause damage. If it is too tight, carefully carve away any burrs or over-extrusion from the slot in the elevon, or sand the control horn to be thinner. Bond the Control Horn pieces (2) into each Elevon (Left Wing and Right Wing) using Cyanoacrylate. Figure-5

6. Glue the Du-Bro Nylon Mini-Hinge pieces (3 per wing, Du-Bro SKU#118) into the recesses along each elevon hinge. Hot-Melt-Adhesive or Cyanoacrylate should work. 3M™ Transpore™ Surgical Tape is also a viable hinge reenforcement solution, and this may be applied now or later in the build.

7. Lightly sand the bonded empennage/tail interface surface until smooth and planar/flush. Test-fit to the Fuselage/Nose to confirm a proper flush joint, and then bond to the Fuselage/Nose using Cyanoacrylate. Set aside to cure. Figure-6

8. Bond the Nacelle Pair Halves together; Be careful here! Each nacelle is composed of an _A and _B piece. There should be four nacelle pieces total, and each of them is unique: An _A and _B that are non-mirrored, and a _A and _B that are mirrored. The _A has no cutout for the stud-arm, while the _B does. The _A pieces are always nearest the center body of the aircraft, and the _B pieces are always on the outside aligned with the servos. Glue the pieces together as carefully and precisely as possible, using Cyanoacrylate. Set aside to cure. Figure-7

9. Lightly sand both wing root interface surfaces on the completed fuselage/body until flush and smooth. Test-fit the carbon-fiber spar and verify that it isn't being halted by any blemishes in the spar shaft in either wing. Get creative if there are blemishes; usually some aggressive poking with the spar will clear these without damaging the 3D-printed shaft. If the spar does not completely fill the spar shaft (7mm inside diameter), such as if the carbon spar is a 5mm round tube, then improvise a shim or other filler to make the fit snug, such as wrapping the spar with tape at the ends and near the center where it will exit into the central body cavity. With the spar present to provide alignment, test-fit both wings to each respective surface to confirm a proper flush joint. Center the spar such that it extends into the left and right wings an equal amount. (640mm is the longest spar length supported. A shorter spar is fine provided it is centered.) Remove the wings. At this point, the spar may be bonded to the body, if desired. (The spar can be installed without any adhesive if you plan on reusing it later, such as if the aircraft is totaled but the spar survives.) Bond either the left or right wing to the fuselage (not recommended to attach both at once) using Cyanoacrylate. Set aside to cure. When the first wing is cured, bond the second wing and set aside to cure. Figure-8

10. Test-fit each Motor Mount (Tilt Mount/Pod) with its respective completed nacelle. Sand or trim as needed such that the Motor Mount is able to tilt fully flush forward, and able to tilt up past 90 degrees of rotation. Figure-9

11. (Nacelle Non-Ball-Bearing Version) For each Nacelle with its respective Motor Mount aligned and present, Ream (Drill to size) using a 1.58mm (1/16 Inch, 62.5mil) drill bit. (Should be 85% to 90% of the diameter of hinge rod to be fitted. Hinge Rod diameter is 1.84mm or 72mil for this case.) Keep the Motor Mount and Nacelle together. Adapt a section of hinge rod to be used as a final precision reaming tool by sharpening the tip using a grinder or emery wheel. Use this improvised reaming tool to ream the hole in each nacelle-mount pair to a final diameter of 1.84mm (72mil). Figure-10

12. (Nacelle Ball-Bearing Version) Refer to the above steps for the non-ball-bearing nacelle design, but use a 3.00mm (7/64 Inch, 118mil) drill bit to ream the shaft. The mechanical friction relationship is inverted, with the motor tilt-mount having a strong friction fit with the insert shaft, and the ball bearings in the nacelle forks/arms providing the smooth rotation interface. Press-fit the ball bearings into the pockets, using mild heat only if appropriate. Improvise a shaft retention solution that also captures the bearings and prevents either bearing from dislodging. Avoid improvising a solution that conducts compression on the nacelle "forks", as this would cause binding and friction.

13. (Nacelle Non-Ball-Bearing Version) Remove each Motor Mount from its respective Nacelle and ream only the Motor Mount hole to the next higher drill bit size, not to exceed 107% of diameter of the the hinge rod. This allows for the outer nacelle arm to have a friction fit retention of the metal shaft, while the inner motor mount is able to rotate smoothly, plastic-on-metal. Too large will allow for excessive play and possible rattling; too small will result in binding. 1.95mm (77mil, 5/64 Inch) is acceptable for hinge rod diameter of 1.84mm.

14. (Nacelle Non-Ball-Bearing Version) Cut the hinge rod pieces, not to exceed 40mm length. Roughen/knurl one or both ends if desired. Press-fit each hinge rod to each Nacelle through the respective Motor Mount. Verify that each Motor Mount can rotate freely and with minimal play in the hinge.

15. For each Motor Mount, ream the Motor Mount linkage mount hole to 1.19mm (3/64 Inch, 47mil) if you are using the recommended 1/16 ball-stud. This can potentially be reamed for a larger ball-stud thread size such as 2-56 (1.84mm, 72mil), use careful judgement in this case. The reamed hole should be about 80% of the major diameter of the threaded ball link to be mounted. Mount the threaded ball-link to the linkage mount hole. The Motor Mount can sustain up to 8mm threaded ball-stud bolt depth.

16. Bond each Nacelle to its respective wing; note that the ball-link should align with the respective servo linkage slot/well. Cyanacrylate works great on PLA, but as this is one of the higher load-bearing structures on the aircraft, epoxy is also a candidate. Verify alignment and tweak/tune the position while the glue cures. Figure-11

17. Bond the Lower and Upper pieces of the vertical fins. Figure-13 (The lower piece is sometimes called the "Strake".) Bond both vertical fins to their respective wing(s). Figure-12 Cyanoacrylate should be sufficient.

Part 2 - Linkages and Component Mounting <a name="buildseq-part2"></a>

1. Mount the front two motors in their respective Motor Mounts. The motor leads may have heatshrink that may interfere or bind the wires; rework this if needed. Mount the motors using the M3 threaded bolt kit that should be included with each motor. Be careful not to have any mounting bolt over-extend into the motor armature/stator. Verify that each motor turns freely and is well secured. Route the wires through the wing and into the main bay, and test the extension-retraction behavior of the wires as the motor mount pitches between forward and hover tilt positions. For each motor, attach the propeller hub hardware kit that should be included with each, such that it can drive a standard 5-Inch propeller.

2. The Rear motor should mount to the tail using M3 threaded bolts that were included with the motor. Route the motors wires through either wire duct channel to the main bay as desired. (The preferred/traditional channel is the left/port side duct, preserving the right/starboard channel for antennas and LED wiring.) Verify that the motor rotates freely and is well secured. Attach the propeller hub hardware kit that should be included with the motor, such that it can drive a standard 6-Inch propeller. Verify that the propeller clears the vertical stabilizer fins, and trim the tips if necessary, or down-select to a 5-Inch prop.

3. The Motor Mount Tilt servos should be tested and centered on a standard RC PWM signal, visiting 1000us, 1500us, and 2000us pulse-widths. Attach a servo arm with a 19.3mm (0.76 Inch) hole-to-center spacing. This value is critical, as the linkage behavior of the tilting front motor mounts cannot be easily modified and any length short of this will result in the motor tilt not reaching the needed angle for hover and anti-torque (yaw) control. An arm any longer than this will not fit in the linkage well/slot. With whatever arm fitted as similar to 19.3mm as possible, test fit the servo into the servo well and verify that between 1000us and 2000us pulse widths, the arm comfortably retracts into the well/slot, and fully sweeps about 90 to 95 degrees from that point. Verify the best servo arm spline position, and bolt/secure the arm in place. Figure-14

4. For each of the Elevon servos, repeat the same procedure as above, but with a servo arm approximately 9.5mm hole-to-center (3/8 Inch). This length can be a bit longer or shorter, the effect is increasing or decreasing elevon control throw. For servos that have an odd-number spline tooth count (such as the Hitec HS-65HB's B1 spline with 25 teeth), to get the most well-centered and symmetric solution, center the servo on a 1500us pulse width and alternate attaching a 4-arm output horn between each 90-degree position to find the most orthogonal/centered position, and then cut off the 3 unneeded arms.

5. Verify that the Link Clevises that attach to the servo arms are able to couple and rotate freely. Reaming each servo arm may be necessary, a value of 1.59mm (1/16 Inch, 62mil) is common.

6. Route the servo wires through the conduit channels on the bottom of each wing to the main bay. Assuming all servos have a 6-inch (~150mm) pigtail, the Elevon servos will have some slack, but the Tilt servos will arrive just barely at the main bay. Servo Extensions can be added, or the servo pigtail can be extended with a section of 3-wire servo lead/cable, or the 3-pin servo connectors can be discarded in favor of direct soldering later if desired.

7. With servo harnessing finished in one form or another, bond the servos to the airframe using Hot-Melt-Adhesive. Note that the airframe may exhibit deformation or melting at the bonding locations, depending on print material used. (This is acknowledged as a somewhat terrible way to mount servos, and will likely be revised in the future. Sorry.) Verify that the servos can produce full torque without becoming detached from the airframe. Also note that alternatives may be explored in servo mounting, such as double-sided adhesive tape, but it is not advised to use cyanoacrylate or epoxy.

8. Form the elevon control rods by creating an L-bend 45mm from the threaded tip of the pair of 2-56 link rods used. Test fit the retaining Du-Bro E/Z Links 0.72 (2-56) Retainer Clip for each bend, and modify the bend as needed and cut flush. Alternatively, a traditional Z-bend can be formed to dismiss the Retain Clips as a requirement. For each Elevon, attach its control rod to the elevon control horn, and attach the clevis to the corresponding servo arm. Detach, turn the clevis, and reattach as needed until the elevon is flush while the servo is centered on 1500us.

9. Cut two (2) 70mm long pieces from a fully-threaded 2-56 rod to form the tilt control rod pair. (DO NOT L-bend or Z-bend these rods.) Soften the cut ends with a grinder or emery wheel such that they will easily thread into the Nylon Ball-Link couplers. Thread on the ball-link couplers and link clevises, and attach each to its respective servo arm or ball-link head. Detach-turn-reattach as needed, such at the servo approaches as close to top-dead-centre (arm retracted into well/slot) as possible, without binding or interference, while the tilting motor mount is firmly forward and pressed against the nacelle. As noted earlier, the clevis should attach to the highest hole in the servo arm, at 19.3mm arm distance. It may be required to bend this rod slightly to allow for the servo arm to fully retract without the clevis impacting the arm. If the servo is straining excessively when the motor mount is retracted, adjust accordingly. WARNING! If the servo is allowed to strain with the clevis binding against the servo arm, the servo will likely fail, via burnt-out servo H-bridge driver, or burnt-out servo motor. Be careful and kind to the servos.

10. The above steps assumed that the servos were powered and commanded during final installation, but for completeness, this step verifies that the servos are able to actuate, and are not being stressed. For each servo, visit 1000us-1500us-2000us and observe deflection on Elevons or Motor Mount and verify that there is no excessive binding or stress. For each motor mount, simulate the load exhibited during forward flight by gently pulling on the motor in the forward direction (about 300 grams force), while the servo is actively commanded to tilt between forward-flight and hover. The movement should be smooth and free of freezing/halting behavior. The elevons should actuate the full range with light loading on the control surface.

Part 3 - Electronics and Final Configuration <a name="buildseq-part3"></a>

1. Solder the Flight Controller as desired. This usually means soldering pin headers to attach the 3-pin servo connectors from the servos and ESCs. Solder a battery connection lead (XT60 or as desired). Power the Flight Controller and verify that it is booting and communicating correctly. Default (likely multicopter) firmware will be fine for the next few steps; be advised that servos SHOULD NOT be connected to the flight controller until the flight controller outputs are configured.

2. Bond the Battery and Flight Controller Trays into the main bay. This can be accomplished using M3 hardware and ample Hot-Melt-Adhesive and some reaming if necessary. The Battery Tray can be permanently mounted, but retain some ability to remove the Flight Controller Tray, as mounting/removing the flight controller requires access to the bottom of that tray. Also note: If using the "Leaf-Spring" Flight Controller Tray, this should have about 30g to 40g of ballast weight attached to the underside of where the flight controller will be mounted. Self-adhesive lead weights work well. The reason for the ballast is to drive the corner frequency of the vibration transfer function well below 20 Hz or so. Also note that the compliant "Leaf Spring" mechanism can manifest harmonic vibration modes if used as-is, and it may be necessary to improvise a viscoelastic dampening solution, such as by injecting Hot-melt adhesive between the folds in the zig-zags, for example.

3. Solder the BLDC Motor leads to each respective ESC, or use bullet-connectors or otherwise as desired. Solder the ESC power connections directly to the Flight Controller's Power-Distribution region, or to intermediate connections as desired. Remove the propellers from the motors. Power on the Flight Controller carefully, such as with a "Smoke Stopper" or a current-limited power supply, and verify that the power system is wired correctly. Program the ESCs for proper rotation direction: Port/Left Motor is Clockwise (CW), Starboard/Right Motor is Counterclockwise (CCW). (If using a BLHeli Passthru mode to program ESCs, the ESCs may be connected to any output(s) on the flight controller.) The Rear Motor may technically be either direction, but I strongly recommend Counterclockwise (CCW). This is a self-tightening configuration, so it is unlikely to unscrew itself in normal operation. This also allows for most non-multicopter propeller options (most propellers are CCW), and to force a consistent tradition that allows for future sharing of PID profiles and control schemes symmetrically. Figure-15

A brief note on prop rotation directions: The reason for the front motors having the Clockwise and Counterclockwise directions as stated is such that when the vehicle is flying in forward flight, and then immediately commanded to hover, the advancing blade(s) are placed as far abeam (toward the wingtip) as possible, while the retreating blade is closer to the main body. This should allow for better roll control through the transition, and by placing the effective centeres of lift for each rotor slightly wider in this condition, any PID control effort is more likely to remain bounded and slightly attenuated by the slightly longer moment-arm. This also follows the typical configuration for quadrotors, which also have the front advancing blades placed on the outside of the arc.

4. At this point, configure the Flight Controller with any specific firmware or settings relevant to controlling a Tricopter VTOL Fixed-Wing vehicle. See ArduPlane Settings below. Attach the servo and ESC headers to their required pins. Install the R/C receiver and connect to the Flight Controller as required. Mount the Flight Controller to its tray, and secure the tray inside the main bay. Power the vehicle and verify Flight Controller orientation is correct, servos are properly commanded, and that control surface efforts are in the correct direction. Reverse and trim servo outputs as necessary in the Flight Controller configurator (ArduPilot Mission Planner or equivalent).

5. (Optional) WS2812 LEDs may be mounted in each wingtip, provided each is a SMD5050 or smaller package, with wires directly soldered to the package pads, and then mounted in the light well on each tip.

6. Stow the ESCs to the side-walls of the main bay using tape or double-sided adhesive pads. Stow any excess wires, and generally clean up the inside of the main bay. Secure the battery using Velcro straps, Tape, or other measures.

7. Mount the propellers back onto to their respective motors. Verify that the rotation directions are correct, as described above in Step 3 and per Figure-15. The rear propeller should have had its tips trimmed slightly if it was necessary to avoid contacting the vertical fins.

8. The Center-of-Mass for the aircraft is intended to be 28mm back from the leading edge of the wing. This is 2mm ahead of the proximate tray mounting holes. The centers of the "Bull's-eye" tactile mounds on the bottom of the wings near the nose are at 28mm. This is an essential metric, and the Center-of-Mass may only be shifted back up to 2mm or 3mm from this point, but with increasing risk to stability. The aircraft will NOT fly statically stable with the CG aft of ~33mm, as the neutral point resides near this point. The Center-of-Mass should be between 26mm and 30mm back from the wing leading edge. Use the Weight-and-Balance Stand and a digital scale, as detailed here: Issue #12 As this vehicle is both a fixed-wing and multicopter, the Center-of-Mass stated here is for the fixed-wing condition, and any measurement of Center-of-Mass should be performed with the motors tilted into the forward-flight condition, with propellers attached, and the lid secured. Shift the battery fore or aft to achieve proper balance, or add ballast inside the tip of the nose if merited. Figure-16

9. Perform any other measures necessary to get the vehicle ready for flight. Decals, paint, or heat-activated covering are possibilities. Vehicle mass should come to an All-Up-Weight around 1000 grams to 1200 grams, with the 3D-printed airframe alone measuring around 460 grams if printed with standard PLA.

Flight Testing <a name="flight-brief"></a>

The clean-sheet approach to tuning this vehicle for flight roughly follows this sequence of steps:

1. Discover the hovering-flight PIDs. This can be done using a test-stand setup and axis-isolation of roll, pitch and yaw. Gain Scheduling for hover-to-forward-flight and reverse transitions can also be performed with a pitch-isolated configuration, but relevance diminishes for angles approaching forward-flight without equivalent relative wind generation. (ArduPlane does this calculation intrinsically, implementing VTOL to other flight-stacks may require developing the Gain Schedule Table.)

2. Continue PID tuning until free hovering hops and static hovering are demonstrated. Tune the position-hold behaviors and demonstrate autonomous Return-to-Land functionality. Demonstrate robust upset recovery and stability. Tune the weathervane behavior until satisfactory.

3. Confirm Weight-and-Balance of the aircraft (26mm to 30mm from the wing leading edge). Verify that pitch is statically stable at cruising speed (19 m/s). Also verify that the aircraft is directionally stable (static weathervaning). Trim the pitch on the elevons to produce a level glide at 19 m/s.

4. Confirm that the control surface deflections are correct for both pilot inputs and autopilot stabilization responses to aircraft movement and pose. Reduce forward-flight PIDs substantially if merited. Hand-launch the aircraft into forward-flight and confirm that it is controllable and stable. Beware that if control throws are too large, the controls can be very responsive and fast. Exit from fixed-wing flight to hover and land safely.

5. If the aircraft is still intact and functional from the previous step, perform AUTOTUNE or equivalent to arrive at sensible PIDs for forward-flight. Tune the waypoint following behaviors and demonstrate consistent navigation. If applicable, demonstrate autonomous landing starting from fixed-wing flight.

6. Hover-climb to at least 50 meters and attempt forward-flight VTOL transitions. Tune the transition behavior until the vehicle consistently enters forward-flight. Transitions should look the same for both human-piloted and autonomous cases.

The vehicle is designed to hover with a nose-high attitude (positive Angle-of-Attack). The reason for this is so that as the nose is dropped to level, the thrust vector brings the vehicle to an initial forward drift. Having established a forward trajectory, the motors are tilted to the 50/50 intermediate point and the vehicle is allowed to accelerate. The motors are then dropped to full forward-flight position.

8. Demonstrate full autonomous missions from launch to landing with forward- and reverse-transition behaviors.

3D Printing Guidelines <a name="3dprinting-brief"></a>

Unlike other 3D-printed R/C aircraft, the MiniHawk does not have any internal structures explicitly specified, such as ribs or stringers; only the outer-mold-line of the aircraft and the bays, wiring conduits, and mounting points are defined. The internal structure is yielded to whatever infill pattern is selected in the slicing software used to convert the volume definition for 3D-Printing. The internal structures may be explicitly defined in a future revision, but otherwise it is up to the builder to define the infill pattern used. The following sections provide recommended settings for each airframe part set (matching the settings in the 3MF files).

Note 1: Forced to occur on trailing edge of wing.
Note 2: Is slightly offset in X-direction for best structure.

For the MH7_ControlHornSet and MH7_TraySet, print 100% Solid or as desired. These pieces may be laser-cut if possible.

ArduPlane Settings <a name="arduplane-brief"></a>

While the MiniHawk-VTOL initially was developed using the BetaFlight avionics ecosystem, ArduPilot is the reccomended ecosystem for the current design. This text section replaces the original Betaflight setup instructions which existed in this section prior to v2.0.0. The old Betaflight setup instructions can be found in the README.md file revision history.

R/C Controller Configuration (Mode 2 Controller) <a name="arduplane-controlsconfig"></a>

Note that MANUAL Mode is a real handful, and should only be used rarely. It is included above as a kind of "cheat" to force the ArduPlane VTOL state-machine to stay in Forward-Flight when Arming, such as when you want to hand-launch the aircraft to skip the VTOL hover and forward transition. First set the aircraft to FBWA using the CH 5 Flight Mode Select Switch, and then turn on the MANUAL Override switch only for a moment and then back to disabled (Flight mode returns to FBWA as set by the Flight Mode switch). Otherwise, if you only select FBWA and then arm, the aircraft immediately reverts to the ArduPlane VTOL forward transition behavior with all three motors spinning in the hover condition.

Flight Controller Connections <a name="arduplane-connections"></a>

The following table works on the mRobotics PixRacer Pro. This should be adapted to whatever ArduPlane-compatible flight controller is otherwise used.

ArduPlane Parameters <a name="arduplane-parameters"></a>

The parameters file below represents the settings used on a typical MiniHawk-VTOL utilizing a mRo PixRacer Pro flight controller. The essential settings should be applicable to whatever ArduPlane-compatible flight controller is used, such as the Matek F405-WING or similar, but some adaptation will be required. WARNING! Modern ESC protocols (such as OneShot or DShot) do not play well with servos if accidentally connected. At best, the servo will filter out the packet, but in some cases the servo will burn out. Don't plug servos into the ESC outputs!

mRo PixRacer Pro: ArduPlane_MiniHawk_mRo_PixRacerPro.param

While the parameters file above has over 1100 parameters, some essential parameters are examined below:

| Parameter,Value        | Notes                                                      |
| ---------------------- | ---------------------------------------------------------- |
| ARSPD_FBW_MAX,32       | Full-Throttle produces around 32 to 34 m/s sprint velocity |
| ARSPD_FBW_MIN,17       | Stall is near 15 m/s for a typical MiniHawk-VTOL           |
| ARSPD_RATIO,1.9936     | Make sure this is calibrated for your aircraft             |
| ARSPD_TUBE_ORDER,0     | While this can be automatic (3), manually set is better    |
| ARSPD_TYPE,1           | MS4525D0 Pressure Sensor, adjust as needed                 |
| ARSPD_USE,1            | Force the aircraft to use the pitot probe, no synthetic    |
| AUTOTUNE_LEVEL,7       | 7 or 8 works best for the MiniHawk-VTOL                    |
| EK2_ENABLE,0           | EKF2 is Disabled, in favor of EKF3                         |
| EK3_ENABLE,1           | EKF3 was used for most flight testing of the design        |
| FLTMODE_CH,5           | Flight Mode Channel                                        |
| FLTMODE1,5             | FBWA, 3-position switch "Down" detent                      |
| FLTMODE2,19            | QLOITER, 3-position switch "Middle" detent                 |
| FLTMODE3,17            | QSTABILIZE, 3-position switch "Up" detent                  |
| FLTMODE4,17            |                                                            |
| FLTMODE5,17            |                                                            |
| FLTMODE6,10            | AUTO, 2nd R/C switch that overrides the 3-position switch  |
| FS_LONG_ACTN,1         | Failsafe Settings used in development                      |
| FS_LONG_TIMEOUT,3      |                                                            |
| FS_SHORT_ACTN,1        |                                                            |
| FS_SHORT_TIMEOUT,1     |                                                            |
| KFF_RDDRMIX,0          | Remove any possible rudder mixing                          |
| LIM_PITCH_MAX,2000     | Pitch and Roll Angle Limits                                |
| LIM_PITCH_MIN,-2500    |                                                            |
| LIM_ROLL_CD,5500       |                                                            |
| MIXING_GAIN,0.5        | Elevon Stick Mixing, value here should be default          |
| NAVL1_PERIOD,11        | More aggressive navigation is possible, 11 to 14 tested    |
| PTCH_RATE_D,0          | Pitch PIDs, these values are mild, AUTOTUNE will increase  |
| PTCH_RATE_FF,0.345     |                                                            |
| PTCH_RATE_FLTD,4       |                                                            |
| PTCH_RATE_FLTE,7       |                                                            |
| PTCH_RATE_FLTT,1.5     |                                                            |
| PTCH_RATE_I,0.15       |                                                            |
| PTCH_RATE_IMAX,0.666   |                                                            |
| PTCH_RATE_P,0.04       |                                                            |
| PTCH_RATE_SMAX,150     |                                                            |
| PTCH2SRV_RLL,1         |                                                            |
| PTCH2SRV_RMAX_DN,90    |                                                            |
| PTCH2SRV_RMAX_UP,90    |                                                            |
| PTCH2SRV_TCONST,0.4    |                                                            |
| Q_A_ACCEL_P_MAX,110000 | VTOL R/P/Y Angular accelerations used in development       |
| Q_A_ACCEL_R_MAX,110000 |                                                            |
| Q_A_ACCEL_Y_MAX,27000  |                                                            |
| Q_A_RAT_PIT_D,0.0005   | VTOL Pitch PIDs                                            |
| Q_A_RAT_PIT_FF,0       |                                                            |
| Q_A_RAT_PIT_FLTD,15    |                                                            |
| Q_A_RAT_PIT_FLTE,0     |                                                            |
| Q_A_RAT_PIT_FLTT,20    |                                                            |
| Q_A_RAT_PIT_I,0.15     |                                                            |
| Q_A_RAT_PIT_IMAX,0.5   |                                                            |
| Q_A_RAT_PIT_P,0.15     |                                                            |
| Q_A_RAT_PIT_SMAX,0     |                                                            |
| Q_A_RAT_RLL_D,0.003    | VTOL Roll PIDs                                             |
| Q_A_RAT_RLL_FF,0       |                                                            |
| Q_A_RAT_RLL_FLTD,15    |                                                            |
| Q_A_RAT_RLL_FLTE,0     |                                                            |
| Q_A_RAT_RLL_FLTT,20    |                                                            |
| Q_A_RAT_RLL_I,0.25     |                                                            |
| Q_A_RAT_RLL_IMAX,0.5   |                                                            |
| Q_A_RAT_RLL_P,0.45     |                                                            |
| Q_A_RAT_RLL_SMAX,0     |                                                            |
| Q_A_RAT_YAW_D,0.02     | VTOL Yaw PIDs                                              |
| Q_A_RAT_YAW_FF,0.1     |                                                            |
| Q_A_RAT_YAW_FLTD,0     |                                                            |
| Q_A_RAT_YAW_FLTE,10    |                                                            |
| Q_A_RAT_YAW_FLTT,20    |                                                            |
| Q_A_RAT_YAW_I,0.1      |                                                            |
| Q_A_RAT_YAW_IMAX,0.5   |                                                            |
| Q_A_RAT_YAW_P,0.6      |                                                            |
| Q_A_RAT_YAW_SMAX,0     |                                                            |
| Q_ANGLE_MAX,3000       | VTOL Pitch and Roll Angle Limits                           |
| Q_ASSIST_ALT,0         | Disable VTOL Assist where possible                         |
| Q_ASSIST_ANGLE,0       |                                                            |
| Q_ASSIST_DELAY,0.5     |                                                            |
| Q_ASSIST_SPEED,0       |                                                            |
| Q_AUTOTUNE_AGGR,0.1    | VTOL Autotune settings used in development                 |
| Q_AUTOTUNE_AXES,2      |                                                            |
| Q_AUTOTUNE_MIN_D,0.001 |                                                            |
| Q_ENABLE,1             | VTOL obviously is enabled for the MiniHawk-VTOL            |
| Q_FRAME_CLASS,7        | Tricopter Configuration                                    |
| Q_FW_LND_APR_RAD,85    | 85 meters for Fixed-wing to VTOL threshold                 |
| Q_M_HOVER_LEARN,2      | Hover throttle setpoint learning                           |
| Q_M_PWM_TYPE,4         | DShot 150 is sufficient and noise-resistant                |
| Q_M_SPIN_ARM,0.05      | 5% Throttle when armed                                     |
| Q_M_SPIN_MAX,1         | 100% Throttle max ESC RPM command                          |
| Q_M_SPIN_MIN,0.1       | 10% Throttle for lowest ESC RPM                            |
| Q_M_SPOOL_TIME,0.5     | 500ms spool time                                           |
| Q_M_THST_EXPO,0.25     | Throttle Expo                                              |
| Q_M_YAW_HEADROOM,50    | 50us Yaw Headroom                                          |
| Q_M_YAW_SV_ANGLE,12    | "12" Degrees for Yaw lean angle                            |
| Q_OPTIONS,1056         | Allow yaw actuation when disarmed, QRTL behavior           |
| Q_RC_SPEED,490         | 490 Hz Motor Updates                                       |
| Q_RTL_ALT,40           | RTL Behaviors in VTOL                                      |
| Q_RTL_MODE,1           |                                                            |
| Q_TILT_MASK,3          | Which motors are being tilted                              |
| Q_TILT_MAX,55          | Transition angle while AirspeedWait is active              |
| Q_TILT_RATE_DN,15      | Tilt Up/Down rates                                         |
| Q_TILT_RATE_UP,75      |                                                            |
| Q_TILT_TYPE,2          | Vectored Yaw Tilt Type                                     |
| Q_TILT_YAW_ANGLE,14    | "14" degrees VTOL hover position                           |
| Q_TRANS_FAIL,0         | Transition Timeout is disabled                             |
| Q_TRANSITION_MS,1000   | Post-transition wait period                                |
| Q_TRIM_PITCH,9         | Pitch offset between forward-flight and hover stance       |
| Q_WVANE_GAIN,0.4       | 0.4 is a good value for this design                        |
| RC7_OPTION,41          | Arming Switch, will disable motors if in flight/hover!     |
| RCMAP_PITCH,2          | Roll/Pitch/Throttle/Yaw (AETR) controls ordering           |
| RCMAP_ROLL,1           |                                                            |
| RCMAP_THROTTLE,3       |                                                            |
| RCMAP_YAW,4            |                                                            |
| RLL_RATE_D,0           | Roll PIDs, these values are mild, AUTOTUNE will increase   |
| RLL_RATE_FF,0.345      |                                                            |
| RLL_RATE_FLTD,4        |                                                            |
| RLL_RATE_FLTE,7        |                                                            |
| RLL_RATE_FLTT,3        |                                                            |
| RLL_RATE_I,0.15        |                                                            |
| RLL_RATE_IMAX,0.666    |                                                            |
| RLL_RATE_P,0.08        |                                                            |
| RLL_RATE_SMAX,150      |                                                            |
| RLL2SRV_RMAX,90        |                                                            |
| RLL2SRV_TCONST,0.4     |                                                            |
| RTL_AUTOLAND,2         | Fixed-wing to VTOL landing behavior in RTL                 |
| RUDD_DT_GAIN,3         | Very mild differential thrust mixing on forward motors     |
| SCALING_SPEED,15       | 15 m/s should be default                                   |
| SCHED_LOOP_RATE,300    | 300 Hz was used in development                             |
| SERVO1_FUNCTION,33     | Right BLDC Motor                                           |
| SERVO2_FUNCTION,34     | Left BLCD Motor                                            |
| SERVO3_FUNCTION,0      | No Connection, 5V BEC connected here for mRo PixRacer Pro  |
| SERVO4_FUNCTION,36     | Rear BLCD Motor                                            |
| SERVO5_FUNCTION,75     | Left Tilt Servo                                            |
| SERVO5_MAX,1800        | MAX and MIN values are hand calibrated, close to 1920/1080 |
| SERVO5_MIN,1200        | Values of 1200/1800 here to prevent damage on new builds   |
| SERVO5_REVERSED,0      | Left Tilt is normal rotation direction                     |
| SERVO6_FUNCTION,76     | Right Tilt Servo                                           |
| SERVO6_MAX,1800        |                                                            |
| SERVO6_MIN,1200        |                                                            |
| SERVO6_REVERSED,1      | Right Tilt is reversed rotation direction                  |
| SERVO7_FUNCTION,77     | Left Elevon Servo                                          |
| SERVO7_REVERSED,1      | Left Elevon is reverse rotation direction                  |
| SERVO8_FUNCTION,78     | Right Elevon Servo                                         |
| SERVO8_REVERSED,0      | Right Elevon is normal rotation direction                  |
| STAB_PITCH_DOWN,2      | 2 should be default, pitch behavior on zero-throttle       |
| STALL_PREVENTION,0     | May be enabled, was disabled for development               |
| STICK_MIXING,1         | How pilot inputs are fused in autonomous modes             |
| TECS_PTCH_FF_V0,19     | 19 m/s cruise                                              |
| TRIM_ARSPD_CM,1900     | 19 m/s cruise                                              |
| TRIM_PITCH_CD,350      | Offset between level-flight pitch angle and tray angle     |
| TRIM_THROTTLE,55       | Typical 19 m/s cruise throttle                             |
| WP_LOITER_RAD,60       | 60 meter radius for loiter typical                         |
| WP_RADIUS,40           | 40 meter waypoint radius typical                           |

Remarks: <a name="arduplane-remarks"></a>

ArduPlane v4.1.0 and v4.2.0dev were used in the development of the Version 2 MiniHawk-VTOL. "Out-of-the-box", ArduPlane has support for a Tricopter Tiltrotor such as this design, and only the parameters need to be set for enabling the VTOL behaviors.

At this firmware version, there are some aspects of how VTOL flight behaviors are handled which are somewhat counter-intuitive. The most annoying of these is that for both piloted and autonomous flying, there is no direct control of the VTOL flight state. Instead of being able to directly command the Forward-Flight condition, the VTOL state-machine requires an airspeed estimate (either synthetic or measured from a pitot probe) to drive the forward VTOL transition to fixed-wing flight. This makes the human pilot merely a voting member in the transition process, with accumulated airspeed determining when the tilting rotors are allowed to fully tilt forward and the rear motor to halt. The developers' mentality treats the hover condition as the default fallback, and any failure to accumulate airspeed in a certain amount of time will have the process revert to hover as a failsafe via Q_TRANS_FAIL. If this transition failure timeout is disabled, the AirspeedWait state will persist and the vehicle will fly in a half-way blend between tricopter and fixed-wing flight indefinitely. For a vehicle design such the MiniHawk-VTOL, over-powered and very fast, it would make more sense for a timeout to result in forcing forward-flight rather than to place the vehicle in this blended behavior, or if using the transition failure timer, to place the vehicle into hover with limited battery at extreme range and altitude, but that is a pull request for another day. And thus, for the current firmware state, it is necessary to be aware of this behavior and to know why it gets stuck in the blended mode.

Another consequence of the forward-transition VTOL behavior is that while disarmed, even though a forward-flight mode selection (such as FBWA) will result in the rotors tilting to the forward position, upon arming, the vehicle will immediately assume the AirspeedWait state, with the front rotors tilting up and the rear rotor spinning up. The throttle setting apparently determines the mix between hovering and forward-flight airspeed wait, but a better solution if you are trying to hand-launch like a traditional fixed-wing is to "bump" into MANUAL mode for a moment. This forces the VTOL state-machine past the AirspeedWait state and allows you to Arm in FWBA mode and have the forward rotors remain in the forward position and also enjoy elevon stabilization and leveling while hand-launching. Just be sure to flip out of MANUAL mode back to FBWA, unless you intend a fully MANUAL hand-launch with no stabilization or leveling.

Transitions from Fixed-Wing flight to hover are typically smooth when being human-piloted, but in autonomous modes, there is a known issue in which the vehicle will nose-dip and then pull up hard when making the reverse VTOL transition to hover. This can be hazardous to the vehicle if negative gee-loading or sudden jerk movement will cause parts to separate. The issue is likely in the TECS tuning parameters, or is an issue local to firmware 4.1 or 4.2.

License <a name="license-brief"></a>

This work is licensed under the Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License. To view a copy of this license, visit http://creativecommons.org/licenses/by-nc-sa/4.0/ or send a letter to Creative Commons, PO Box 1866, Mountain View, CA 94042, USA.

The Ardupilot and Betaflight software configuration text files provided here likely fall under GPL-3.0; both projects are licensed under GPL-3.0 at the time of this writing.

MiniHawk VTOL - Design, Documentation, Images and all other Artwork; by Steve Carlson
https://github.com/StephenCarlson/MiniHawk-VTOL