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VTOL reversed trirotor tilt rotors

Hello, I’m new on this forum and I recently started to play with ardupilot. A fantastic resource!
I’m planning to modify a foam plane to make it VTOL ready and I’m following to “reversed tricopter” configuration with all 3 motors fully tilting. I’m ready with mechanical design and I’ve already realized tilting nacelles that work fine.


My question is: any straight suggestion about parameters’ config. for this reversed layout? Q_FRAME_TYPE and Q_FRAME_CLASS? Propellers rotation: it seems that could work both with all 3 at same direction or front and one side CCW and other side CW: is that correct?
Any possible suggestion and information is extremely valuable for me…
Thank you very much in advance.
Paolo

Hello Paolo,
welcome to the VTOL area. Could you post a sketch of the planned VTOL so that we can better judge what exactly you have in mind ?

Rolf

Dear Rolf,
thank you very much for your reply.
Here is the plane I intend to convert to VTOL


And this the scheme I intend to realize.

As you can see the 2 wing’s motors will be only 50mm behind CG, so they will carry about 90% of model weight. Front propeller will act mainly as balancing vector.

Total expected model weight is 2800g.

What do you think?

Paolo

Hi Paolo,
please allow me some thoughts on the design:
a) Motors and tilt mechanism at the wing tips require very stable and therefore heavy wings to avoid resonance flutter during hovering.
b) Are you sure that when the motors are tilted forward, the centre of gravity is safely within the manufacturer’s recommended range ?
Perhaps it would make more sense to mount the rear engines on a boom on the fuselage behind the wings ?
The rear engines should run in opposite directions.

If you are sure that you want to build the plane as a reverse-tri-tilt, I will of course help you with the parameterisation.
Due to the small number of users the reverse function is not officially supported yet, but thanks to @iampete Peter Hall reversed tri-tilt VTOL is supported by master firmware.

Rolf

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Dear Rolf,
your thoughts are very appreciated and needed.

Wings are very stiff, there is a carbon spar (squared section tube) from root to tip, so I’m quite confident on that.
CG will be ok when motors are tilted forward.
About reverse tri tilt configuration… yes I like that; that makes the overall result aesthetically more clean and … better :slight_smile: ! I know that it is challenging but I believe that challenges are the reasons for our hobby.
I’m preparing now the front tilt mechanism and I’m going to order motors, escs and propellers (thank you for the clarification about rotations).
As soon as ready with mechanics your help will make the difference.

Thank you again.
Paolo

Hi again.
Just an update: front tilt mechanism works fine. Few pictures.
Have a nice day
Paolo





Hi, Paolo,
that looks good.

For the reverse-tri-tiltrotor function you have to load the master firmware and set the following parameters:
Q_FRAME_CLASS,7
Q_FRAME_TYPE,6

So that all engines tilt Q_TILT_MASK,11
For Vectored-yaw Q_TILT_TYPE 2

I am curious to see how things will go on

Rolf

Hi Rolf,
now I need to receive all components, then we’ll start! :slightly_smiling_face:

thank you.
Ciao
Paolo

Hello Rolf!
I’m moving with hardware and I’m starting to test motors.
I’ve found already a problem: front motor has reversed stabilization action.
I mean: in QSTABILZE mode, when I move manually nose down the nose motor’s speed goes down, when I move nose up the nose motor speed goes up.
So the correction is reversed.
How can I fix that? Is it needed to reverse PID?
If I reverse pitch PID, what about elevator? (that will be then wrongly stabilized)…
Thank you in advance.

Paolo

Just thinking…
reading about your experience with Mozart I understood that reversed PID issue for reversed tricopter have been fixed and working with official Plane firmware release.
Could it be that latest firmware (I’ve just updated to 4.0.6) is not more working for that configuration? Could it make sense to upload an older firmware version? If yes, could you please advise about which version did you test as well working?

Thanks again.
Paolo

The code is there in plane 4.0.6, you need normal PIDs and the frame type set to 6 for ‘plus reverse’

Dear Peter,
thank you.
That’s strange… I know. I’ve settled as suggested from Rolf:
Q_FRAME_CLASS,7
Q_FRAME_TYPE,6
Q_TILT_MASK,11
For Vectored-yaw Q_TILT_TYPE 2

Roll correction on motors is ok.

When I test Pitch corrections I see that elevator is ok but not nose motor (reversed correction)…
Is the front motor ESC port configuration correct as SERVOx_FUNCTION=36?
Any suggestion about what to check?
Sorry to bother and thank you.

Paolo

36 is correct, Strange, can you post a vid and log of whats going on.

I’ll do as soon after office.
Thank you

Dear Peter here is a poor video that shows (hopefully) what’s happening.
You should see also that elevator is correcting fine…

And here is the link to Log file
https://drive.google.com/file/d/1UKIP70ziXCZu8Hjj4J7lukaUbijrNb9x/view?usp=sharing

Thank you in advance

Hum, its defiantly backwards, cant see any why tho.

Can you try on Master (4.1.0), you can load with ctrl + q on the MP load firmware screen. Usually not recommended to fly with master unless you know what your doing, but it will be useful step to try and debug this issue.

Dear Peter,
good morning.
Just uploaded Master firmware 4.1.0 and tested.
Situation is not changed: nose motor has still reversed correction. Elevator correction is ok.

Just to give all possible info: I’m using a Pixhawk 1MB, nose motor esc plugged as below


Here, if useful, the saved parameters list as I’ve today
Configurazione 14_09_2020 19_57.param (20.7 KB)
thank you again

Hi Paolo,

I faintly remember that the pitch issue did not occur after I completely reloaded the firmware new by loading rover-firmware once and then loading the Arduplane firmware again.

@iampete: Just to confirm: master is still required or is the reverse-tri-feature also included in the current stable ?

Rolf

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