One motor spinning faster than all of the others

[dartuav (Will)]

The drone pictured above is functioning as a tricopter with the same signal being sent to the pairs of motors on the left, and the pair on the right. We diagnosed that one of the motors is rotating faster than the rest independent of the ESC which is unable to be corrected since both motors receive the same signal. What could be causing this?

[dkemxr (Dave)]

This seems to me to be a flawed tricopter VTOL strategy. The motors driven in parallel will need to rotate at different speeds to produce the same Roll moment and of course they can’t. So at best it’s inefficient, at worst a control stability problem. Is there enough thrust for one motor on each side to get off the ground?
Also, these questions belong in Plane>VTOL not Copter.

[Allister (Allister Schreiber)]

Fixing Roll Instability in Tricopter

Im using a homemade tricopter airframe with a pixhawk flight controller and mission planner, using a ps4 controller as my controller. I am trying to trim the motors for a stable takeoff, every time I try to takeoff as I increase thrust the aircraft rolls right. What parameters can I fix to correct this? I’ve tried changing the rc_trim values of the motors but this doesn’t seem to do anything. Thank you

Uncontrollable after takeoff

Hello, I am making a VTOL tricopter to plane drone for a college capstone course and am having some issues with control. We need to throttle up the motors pretty fast to achieve takeoff without the plane tipping over and once its in the air it will rise stably for about a second but then it seems to freakout and flip out of the air. We are using a Pixhawk with a PS4 controller connected to our computer in order to control it. It seems to me that if it can takeoff stably then the issue would be …

This drone is very popular. A lot of people asking about it.

[Daniel_Lader]

We’re somewhat limited in budget and supplies so we needed to use the ESCs and motors we already had, with these and 10 in. props we weren’t getting enough thrust with only two front motors. We have thought about going to 12 in. props to increase thrust but my partner in charge of sizing the props, ESCs, etc. says increasing prop size could put too much load on our ESCs.
All that being said we have tried to test with only two motors a couple times, and the drone still rolls to one side as soon as thrust is beginning to increase. This makes me think there might be a FC calibration issue.

[dkemxr (Dave)]

@Daniel_Lader

All that being said we have tried to test with only two motors a couple times, and the drone still rolls to one side as soon as thrust is beginning to increase.

If the outputs are maxed out because there is a lack of overall thrust that could happen.

[Daniel_Lader]

I have very limited programming experience but I know ardupilot is open source and I have several comp sci friends, do you think it would be at all possible to add two motor outputs to the existing tricopter code, or is that not really feasible?

[dkemxr (Dave)]

There are some Custom Motor Matrix Lua script examples you might base it from.
Lua scripting examples
If it would work at all I think you will need independent control of all motors.

[Daniel_Lader]

That’s what I assumed. I don’t know if you have any experience altering programming like that, but would this be a very complex endeavor?

[dkemxr (Dave)]

Start another post and ask about Motor Matrix Lua Scripting and describe what you are trying to do.