We’ve adjusted the PWM values for the tilt servos to range between 1025 (in quad mode) and 1990 (in forward flight). So that is not the reason why the PWM value goes only up to 1507. However, I just noted (from the graph you posted above) that the tilt servo travel during the attempted forward transition was limited to a couple of seconds before the plane was switched back to Qstabilise. So off the top of my head, the increase in PWM from 1025 to 1507 appears to be in line with the value set for Q_TILT_RATE (i.e. 25 deg/s).
The point I was trying to make was that C13 and C14 are AUX5 and AUX6 outputs that control the tilt rotor servo positions. The tilt servos can only follow this PWM setting, therefor there is nothing wrong with the tilt servos that Jacques is currently using.
According to the log, the mode was only in FBWA for about 5 seconds. This is controlled by the pilot. It would seem that the limited motor tilt is effect not cause. Since the plane immediately starts rotating yaw, the airspeed estimate (because there is no AS sensor) limits the tilt transition because the plane isn’t moving.
Sorry, I had not seen the picture in this thread. With that picture you have of course found the reason for spinning around the vertical axis immediately after initiating the forward transition due to only one motor is tilting.
Tiltservo-Output is correct, so it is defintiefly not an arduplane issue and i also suspect an impaired servo or BEC.
The reason is that the servos properly stop at 45° (halfway), as set by parameter Q_TILT_MAX = 45.
It means, that the tilting stops at Q-TILT_MAX until transition speed ( ARSPD_FBW_MIN ) is reached Only from then the motors tilt completely.
I picked out a little movie from our tritiltrotor “Mozart”, where you can see the two phases quite well Mozart Routine on Vimeo
Ok, thanks, it is good to know that while on the ground the motors can move between 1025 and 1990 PWM, but while armed and in the air, it requires ARSPD_FBW_MIN to go beyond Q_TILT_MAX.
The assumption is that Jacques has tested the forward flight position many times on the ground. His suspicion is that motor gyroscopic forces are preventing proper movement. You suspect an impaired servo or BEC. I guess we’ll see what the result of his full power ground test.
I might suggest that Jacques consider using vectored yaw to improve the current yaw performance.
Jacques actually tested it on the ground, where it appeared to work fine (switching from QStabilise to FBWA actually caused the correct tilt servo actuation).
Unfortunately, the current firmware does not support vectored yaw for tilt rotor quad planes of this sort (with two forward tilting rotors and two rear pure VTOL motors).
I found a post from Tridge from last May 2018 where he talks about a 4 rotor tilt quadplane. It sounds like what is not supported is when all 4 rotors tilt. If only the front rotors tilt, and are used for forward flight, then you can use vectored yaw. You’ll need to change Q_TILT_TYPE to 2 and your AUX5/AUX6 functions from 41 to 75 and 76 for left tilt and right tilt. Perhaps my interpretation is incorrect so maybe someone else can post about it.
Following the “impaired servo” thought-line, I noticed that the motor mount is 3D-printed. Could it be possible that it’s flexing due to the prop torque causing it to bind? Does the log show an unusually high amp draw at transition; within that 5-second time frame? The ground test with full throttle could definitely reveal that, if it was the case.
Hello Rollys,
The motor mount / tilt mechanism is both very tough and stiff. So that is unlikely. From the logs, I didn’t notice a noticeably high current draw during transition. Ground test with props off didn’t reveal much either. As the next step, we’re planning on conducting a props-on full-throttle ground test in a few days time to simulate the situation at ground level.
Thanks,
Wasim
I’m in the process of testing a four-motor quadplane with the front two tilting. I can confirm that vectored yaw works just fine, the same way it does on trimotor builds.
Hi Greg, in regards to your earlier post where you mentioned that you don’t believe this is an issue with tilt servos/mechanism. Something to bear in mind is that the RCOU PWM values for both tilt servos were identical. You can also see that in the graph you posted earlier (the green line for RCOU C14 sits behind the red line for RCOU C13 and the max/min and mean values are also identical). However, the right tilt servo did not physically move, which is very clear from the 4 x video frame grabs I posted above.
Based on this, would you not agree this is a hardware failure?
By the way, we do have a pitot, but we overlooked the parameter to make it active (doh!). Still, some are flying VTOLs successfully with synthetic airspeed calculations, so this should not be an issue. Even if airspeed measurement was an issue, it would not make one tilt servo react differently to the other.
Not intending to pick an argument here, appreciate your input as always, but would just like to understand why you have disregarded hardware failure when that seems to be the only logical conclusion.
I think these discussions are well intended so I never feel they are argumentative. We all learn from the various setups…both successful or not.
My point in disregarding the tilt hardware was based upon your previous projects. You are a meticulous builder and have made many interesting and awesome conversions. So my assumption was that you have already tested the tilt rotor hardware many times. Further, we are using similar (if not exact) components on other projects like the Nimbus 1800 VTOL and experience no tilt rotor issues when the motors are spinning.
One difference I see in your project is that you are not using vectored yaw. Thanks to James, we have confirmed that it is now a possible option. Another difference is that in previous projects similar to yours, I have seen both front tilt rotors tied to the same mechanism or output channel so yours is slightly different.
I wish I could pinpoint a solution but there are many variables. I know that swapping out the tilt servos is not an easy task but perhaps it will fix the problem or let us look elsewhere.
In this case, if it was a hardware failure due to workmanship, then that will sit with Wasim, as he built the aircraft and I’m just doing the testing
But I can tell you it is very well built. I actually had some concerns about the first 3D printed parts he was using for the motor mounts, but he printed some beefier ones and they are very strong indeed. One thing I’m leaning towards is possibility of the BEC not being able to maintain sufficient current for both motors. We are going to check that out and also do some ground tests at full throttle and try actuate the tilt.
Here’s an update: After a series of ground testing, we’ve identified the problem - it was the case of an impaired BEC, and we’ve managed it sort it now. Thanks for your help.
However, I have got another question regarding yaw control in vectored tilt-rotors. When a plane is configured as a vectored tilt-rotor, does the yaw vectoring work in conjunction with differential (quad) motor speeds to control yaw, or is it just vectored yaw (without the use of differential speeds in quad motors)?
Yes, the vectored yaw does work in conjunction with the motor torque. Greg’s setup doesn’t do this because it’s a tricopter-type frame, so there is no way to properly use torque to yaw while remaining stable. This is true on all tricopters, not just vtol tricopter-planes. But on a setup like yours, it will still use motor torque.
