Quad plane tilt rotor H-setup, front motors face up, rear face down

Motor/servo attachment. Thanks for the comments about the servo and the mounts. Biggest issue I have is with the centering on the digital servos. They center well, but not consistently at the same point and the splines do not have enough latitude to get a consistent centering point for all four servos. Would a servo programmer help with this?

Servo to boom.

It looks solid enough. What is the servo number?

You should be able to get good information on the performance from your hover testing.

Good luck!

I got to make another comment. Those carbon fiber square booms you are using are pultruded. They have no interweaved fibers, only strands running in parallel from one end to the other and only held together by the resin. While they are great to take bending (to some degree) or pulling forces, they are not great at resisting torsion. Your way of mounting the motors introduces torsion into the booms. I would recommend checking the booms frequently, testing if one is softer than the others and looking for cracks. I used those booms on one of my bash around copters and one boom eventually became so soft, it allowed the motor to be twisted 15° left and right without much force. And those booms where only 20cm long. They also like to split at the seam, where the two halfs were glued together.

Servos are MG996R Digital Metal Gear. Thanks for your comments.

Hi Tim,

interesting construction. Some hints from our tri-tiltrotor experience:

I would choose an X-frame logic instead of H-frame logic, so that the torque of the propellers during forward-tranistion counteracts against disturbances at the roll axis. See: Tiltrotor support for plane and Tiltrotor support for plane

For the tiltservos you should each use a separate output (function 41)

Dont forget to set:
Q_ASSIST_SPEED 0 (tilted Motors cant help prevent stalling)
Q_TRANSITION_MS 0

Adjust the following parameters to your individual plane characteristics:
Q_TILT_MAX (Max. tiltangel while accelerating from hover to planflight and waiting, that FBWA_MIN will be reached)
Q_TILT_RATE_DN , Q_TILT_RATE_UP (degrees/second)
ARSPD_FBW_MIN xx (m/s, at thist airspeed the tiltable motors turns immediatly to plane mode and should be a little bit above stallspeed )

Be carefull: Do not accidentally switch directly from QHOVER to MANUAL MODE (instead FBWA) without enough speed or height above ground
Tiltrotor support for plane

Curious about your progress, good luck
Rolf

Rolf, thank you so much for your suggestions! Not sure what you mean about separate output for tilt servos. Do you mean each individual servo should be on its own channel? I had planned to use a combination of y-cables and a servo reverser to connect them all to the same channel (channel 11 was the indicated channel for doing this). I will definitely look into the x-frame logic; h-frame just seemed natural as that’s how the setup looks, but I can see that the physical setup doesn’t have much to do with that setting.
I am not fully understanding the modes, I guess I need fwba for the forward flight setting and what do you suggest for the hover mode? I can see where manual mode would not be a good thing!

Yes, this allows you to adjust each tiltservo precisely (SERVOxx_MIN/MAX/REVERSED ).

I suggest first to test QStabilize and Qhover flights like a copter. Then - without props on the bench- first test correct aileron/rudder/elevator moving in manual AND FBWA mode before real flight.

If you use an airspeedsensor, make sure it is calibrated correctly.

Regards Rolf

Thanks, Rolf! If I understand correctly, this will allow me to adjust for centering differences among the four tilt servos. I truly appreciate everyone’s input into this discussion.

Tim

New question. I have been reading about powering the pixhawk servo rail as I need to power four flight servos (rudder, elevator and two ailerons) in addition to the four tilt servos. Can I do this with a 2000 mah nimh pack connected like another servo to the output rail and if so, I don’t need the zener diode, right? I am thinking it’s probably not a good thing to use one of the ESC’s BEC to power the rail, as everything would ultimately get its source from the lipo. Your opinions are appreciated, especially as I get closer to completion on this.

Thanks - Tim

By the way, the 2000 mah pack is 4.8 volt. I’m guessing a 6 volt pack requires the zener diode.

Adding another battery means adding another point of failure, not redundancy. The lipo is monitored through the power module. You and the FC will know when it is empty and then failsafe kicks in or you decide to land beforehand. How are you going to know what the state of the nimh battery is? Better add a standalone BEC connected to the main lipo, with enough current rating plus a bit headroom to supply all your servos. Test it on the ground by moving all the servos and see if it drops out, before the first flight.

Thanks. I do appreciate your comments along with those who continue to show their support.

Initial testing of tilt-rotor:

Nice test video! I assume that the Pixhawk will eventually go inside the fuselage?

Thank you, Greg. Unfortunately not much room in the fuse as I probably will have to use a 4s lipo inside to get this off the ground. Weight is also a concern at this point. It is close to 5 pounds now loaded. I built a small platform where the canopy goes, and the pixhawk sits on it. (It’s not fully attached to the platform in the video) As you can imagine, the # of wires is considerable. 8 cables [(4) servo/esc cables and (4) 12awg power lines] to each of the carbon fiber assemblies.

Yeah, it was a challenge without adding the extra servo wires for the tilt mechanisms like your setup. However, I sometimes enjoy stuffing 5lbs into a 3lb box. :grinning:

Thanks for the photos and explanation, Greg. I am nearly ready to hover test. I had to work through some issues regarding the primary (airplane) flight control directions, neutrals, and min/max. I did that by switching from fbwa/qstabilize to manual/stabilize (i.e. airplane) modes (on the bench, of course) and set the centering/servo directions and min/max. Once I felt those settings were valid, I switched the modes back to fbwa/qstabilize/qhover. Here’s my question: Assuming that I have used channels 5-8 correctly (assigned the correct motors and set motor rotations correctly) can I reasonably expect that the pixhawk will make (in hover modes) the appropriate motor speed corrections (fore/aft, left/right, and yaw) based on how the aileron, elevator and rudder settings have been set up?

Hi Tim,

what do you mean with aileron, elevator and rudder settings in the context of hover modes ?

In hovermodes (QSTABILIZE, QHOVER, QLOITER, QLOITER… ) the “appropriate motor speed corrections” depends on good Q_A_RAT_xxxx PID - parameters (like a copter) and have nothing to do with the rudder settings.

Good luck
Rolf

Thank you for your reply, Rolf. I acknowledge that I did not express myself well. What I meant was that I find it difficult to judge whether the appropriate corrections are being made (on the bench) for the four motors. It is easy to tell if the appropriate corrections are being made to the airplane flight controls (aileron/elevator/rudder) by tilting the aircraft (while in stability mode) and watching the corrections made by the pixhawk. What I was hoping is that if I have set the quadplane up correctly as far as the aileron/elevator/rudder is concerned, will the appropriate settings carry over to the motor controls? Or will I have to determine that from hover testing. Doing that is time consuming as I am not using telemetry to make computer corrections.