I finally had time to assemble my version of the VTOL Bronco. It's a carbon copy of the FT VTOL Bronco, except my VTOL tilt is 3D-printed and based around common T-rex 450 parts. I'm running OpenAero2 VTOL with CCPM 6 channel Rx. All stock FT hardware otherwise.
I drew up the tilt in Solidworks. It is pinned using barbecue skewers just to keep a little heritage in the build.
Ball bearings used for the tilt are from a T-rex 450 spindle. I used the T-rex 450 spindle for the tilt shaft to help keep the parts cheap and easy to find.
I then 3D-printed the pieces on an Ultimaker2 3D printer and installed the servo, bearings and motor.
I'll submit my OpenAero2 VTOL settings in the next couple of days after I get them dialed in, but here are a few things I've noted so far.
Mechanical geometry has to be really closely matched to your servo pwm at 1.9ms-1.1ms. This is because I'm doubling up my gear channel for the profile trigger as well as one of the tilts. The profile channel is set to 'gear' and when I trimmed the travel initially (long on the horn), I couldn't get full full P1.0 and P2.0. I changed the mechanics to more properly align the pwm out and now I'm killing two birds with one stone and don't have to use a y-cable. I like this setup because I really wanted to put the servos on separate channels as well as opposite sides of the respective booms (for symmetry). I'm also running each aileron on separate channels so that I can run a flap mix in the transition. I'm not liking how much servo bind there is with flaps down so we will see if I use it. I really need to redo my hinges for less bind.
Maiden went ok. Transition was fairly uneventful but needs some nose down offset. The big adjustment needed is tuning the low pass filters. The hover work at the end really demonstrates the system lag effecting the phase/gain margin and going slightly unstable.
Fly Fast Fly Safe
-Beall
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Chapo for taking the task and making it work. I waited so much time for FT to publish something for a VTOL (chimerA, bronko), but I guess there wasn't enough pressure from the community.
I am really happy to see the result. It is flying so well.
I will be waiting for the plans and hope to have some time to build one too!
Keep up the good job!
Tal
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I'm also building the FT Bronco for the exact same reason.
I've build a scratch build VTOL before:
https://www.dropbox.com/sh/s94slf13qczjuxs/AABB0P4R9vUBQfeDYuqPQwlda?dl=0
but the frame in combination with the relative long motor axes made it a very shaky aircraft.
The OpenAero software could not compensate for it.
I'm planning to re-use the printed swivels.
what did you use as a control board, KK? (OpenAero2 VTOL)
Can I contact you once I start configuring my OpenAero parameters?
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If you aren't using the S.bus method of communicating with the FC, I recommend it. In fast mode it has a faster loop rate for lower latency which allows for higher P, I, and AL values without oscillations.
OAV has travel limits so you can prevent any servo jamming due to mixing flaps. There is really no need to mix flaps into the ailerons though.
I usually use a 7 or more channel RX and a TX with 7 or more channels. That way the flap output can be used as the transition control input to OAV, and the TX can be programmed with mixes to output the same signal on two other RX outputs, usually AUX2 and GER. Those two outputs can then drive the two tilt servos with independent travel control in the TX. That avoids the issue of matching the transition control travel into OAV with the mechanical travel needed by the tilt servos. It also allows a rudder mix into the tilt servos within the TX for enhanced Yaw authority. In some designs this eliminates the need to tilt the back motor for yaw control.
Lots of folks making this design or similar recently have had difficulty getting good pitch trim throughout the transition. This is not due to a deficiency with OAV but due to learning curve issues with knowing how to use it. I am glad to see your transitions are so clean as it helps to prove that OAV is more than capable.
If you like, I would be happy to include your FC parameters in the spreadsheet of examples that we provide as part of the documentation for OAV.
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You might double check your design to make sure the back motor is 2 units of measure behind the CG, and that the two front motors are 1 unit of measure ahead of the CG. If not, you will need to tune down the throttle volume to the front motors in P1 (hover mode) for proper pitch trim.
The best way to verify trim in hover is to temporarily turn off all I and AL feedback to the motors and hover at just a few feet over soft grass in no wind. If you have to hold constant stick input then you are out of trim. You can't move the CG to fix it because the airplane CG needs to be in the correct place, but what you can do is reduce the throttle volume on the high side motors. You can also increase the throttle volume on the weak motor but not by much because going over 100% creates a flat spot in the throttle curve. I recommend using the throttle volume to fix this, not the offset curve, because you want a constant ratio of power to all motors based on throttle stick input. In other words, you don't want changes in throttle stick to cause an unwanted pitch disturbance.
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I have been waiting to build my Bronco VTOL. I have all the necessary parts except for the motor tilt mechanisms, and I don't have time to build them. I would certainly consider buying a set from you, if you decide to sell them.
Thanks
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I too hope that the FT team release this vtol aircraft.
Great work!
Nick
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Thanks
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Great work on the VTOL... Could you please share the 3d print file or the .dxf file?
I would be interested in building one too...
Thanks!
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