u7, a2 throttle calibration issue?

[Pumpkinguy]

Folks. I need your help.

Tmotor u7/490, t80a and a2 fc.

I throttle calibrated the esc's using f4 channel mapped to my throttle. It went perfectly according to the chimes. (I will note that I removed all red wires from esc's before hand)

Here is my problem.

Motor test in assistant does not work.

Csc command will not start.motors unless I move throttle up near the mid point. Motors spin up but 3 of 6 will shut down in throttle is at mid point and the other 3 shut down at one notch below mid point.
This seems like a calibration issue. I've calibrated twice now. Same problem only on different motors.

Any insight would be appreciated.

 

[econfly]

The problem is that the A2 is sending throttle signals that are not a function of your radio end points. So, calibrating the ESCs to the radio end points is not the right thing to do. I know everybody does it, but I have yet to hear a good reason for why they do it.

Calibrating the ESCs to the radio tells them to adjust their start signal based on the radio's throttle low end point (and, less relevant, to adjust the throttle curve based on the radio's high end point).

But, when you calibrate your radio to the A2 you tell it the endpoints for the throttle, A, E, etc. and then the A2 knows the limits of the incoming signal from the radio. That's all on the input side of the A2. The output side, however, does not change. This is very important. The signals the ESCs get from the flight controller are not a function of your radio's channel end points if you set thing up correctly.

Say, for example, your radio throttle pulse width signal ranges from 950 microseconds to 1900 microseconds. When you calibrate the ESCs with the radio throttle output you tell the ESCs that 950 microseconds is the lowest throttle signal they can expect. Then, the ESC firmware automatically picks a start level based on that (say, 1100 microseconds pulse width). Now you hook the ESCs up to the A2. The A2 output is the same regardless of your radio endpoints. So, it's only by luck that the A2 motor start signal can get the ESCs going.

Two ways to fix this: (1) The A2 motor start signal pulse width is affected by the motor idle speed setting, so you can try to fix this by selecting a higher idle speed. Or, (2) move the low endpoint on your radio throttle up a bit and re-calibrate the ESCs.

There is no easy way to calibrate correctly (i.e., to the A2, and not to the radio). Best is not to calibrate at all. If things won't work absent calibration, then calibrate to the radio with the stock end point and adjust upward on the end point and re-calibrate if the motors won't start when the ESCs are connected to the flight controller.

 

[Pumpkinguy]

Eco. Like always I appreciate the time and energy you spend trying to help guys like me that have just enough knowledge to be dangerous.

I did play with the idle speed with no results. I've been in the shop and found a fix before sing your reply in my email.

I'm gonna spell out what happened for guys searching for info in the future.

First calibration I did them one by one. Motors 1, 2 and 3 were starting and stopping at different points in the throttle range than 4, 5 and 6.
I did a second calibration. Again, one at a time. This time the odd motors were in sinc and the even were in since but not in sinc with each other.

So I made a harness. Calibrated all 6 at once. Still, the odds and evens were grouped. Can you say "WTF?"

Finally I calibrated them using my futaba 7008rx. Now, everything is perfect. I don't understand why it's working now. It just is.

 

[econfly]

My guess is that the A2 sends an adjusted PWM value to the F1-F4 ports, so your throttle mapped to the F4 port on the A2 was producing a different endpoint than the raw throttle output on the 7008 receiver. Why odds/evens would be synced differently could be related to startup signal from the A2. I don't know, but I'll guess that the A2 sends slightly different startup signals to counter/clock motors for some reason, but I have not measured to confirm.