I use an APM 2.5 running arducopter FW 3.1. It has flown for many months very well. After a crash which broke the micro usb port off the circuit board, one of the motors begins to spin only after the other three are at nearly 15%. I can take off, but the one ESC/motor combination does not provide as much thrust as the other three which seem quite balanced. Once I switch to loiter mode, the quad will hold its position. If I return to stabilize, then the weaker motor drops it's thrust lower than the other three.
I've calibrated the ESC/motor sets simultaneously and when initializing thrust, the lazy motor starts up at the same time as the others and increases in the expected way. Once, I arm the quad, the motor goes back to its lazy ways.
I have the same effect if I replace both the motor and ESC for another motor and ESC.
Since I have no usb port, I can no longer download logs and can no longer upgrade or replace the firmware on the APM.
Any ideas?
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Maury, your analysis was absolutely correct regarding the onboard ACC. I did not even check this assuming nothing had changed. With telemetry transceiver in place and connected to MP, the horizon was not level on MP when the copter was level. After calibrating the compass on the APM 2.5 using MP, the copter flew like a charm again. Once in the air after a smooth take-off, I checked the GPS capabilities in loiter and rtl flight modes - they work fine.
Thanks for your help!
To clarify the last comment a little bit. I suspect that another properly calibrated flight computer if available will not have the problems you are having now.
To test the ACC without access to the USB / software side of things I would imagine that you'd be able to slightly raise all but the slow side. The APM may be slowing down that motor because it thinks it is higher than the other 3. Take 3 equal (small pieces) of foam and temp tape them to bottom of the other 3 legs on your copter. do it in small increments so you don't cause a dangerous situation but if as you progress the problem is going away then you need an ACC recal and USB repair.
Maury, thanks for the suggestions. I do have the USB connector that was pulled from the board at the crash. I will attempt to solder it onto the board this weekend. It still seems like a great flight controller and is worth a bit of attention. I do have telemetry, but when trying to download logs, it times out. I may have some setting incorrect. I'll look into that as well.
Maury, the contacts on the USB port are simply too small for me to try to re-solder. The board is fine otherwise - there was no physical damage to the board. Since I had a pigtail permanently connected to the micro USB port, it was yanked off the board properly without damage to other components or the board itself. I may simply be looking at a replacement for the APM 2.5. However, since it is an older model, they seem to be quite high in price. Any other suggestions before I begin a rebuild?
"I have the same effect if I replace both the motor and ESC for another motor and ESC."
Are you saying a certain APM output, like "Output2" is spinning any ESC+motor later ? (very unlikely)
or are you saying that a certain *motor* always starts late regardless of ESC it's connected to? (very easy to explain)
- you need to narrow it down, find one thing that always does it, no matter what you connect it to (swap motors/esc)
Andre, thanks for the reply. My ESCs are soldered to motor leads. So swapping motors with ESCs will take some work. I will first try connecting signal wire of lazy motor to a different output to rule out unlikely problem in the apm. If it is not the APM's fault, I'll warm up my soldering iron.
you may try to swap outputs, but unless there is reason to believe that one of the ESC's is not calibrated (different kind, calibration is disabled in ESC or similar) , I am pretty sure you have a defective motor.
One winding can me damaged without any other signs.
There are a few methods to detect it; the thrust will be lower, and the inductance and/or resistance in one of the three ways you can measure will be changed. - that requires an inductance meter and/or low-ohm meter to detect.
Andre, I swapped the ESC and "lazy" motor with a pair that I know is working. The same lazy startup occurred after arming the copter. However, the calibration worked fine and all motors start up at the same time. I then, swapped the control leads for motor/ESC combination #2 (the lazy startup on arming) and #3 (that starts up immediately just like #1 and #4). The lazy motor/ESC is now #3. So, I think now there truly is something wrong with the APM 2.5. It seems the only recourse I now have is to buy another APM 2.5 and swap it out. All motors and ESCs seem to work as expected otherwise. Any additional thoughts?
I do have an inductance meter. I will test that first. Calibration send to work fine and ask other aspects of the APM seem to appear normal. Thank you.
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