Discussions

Erratic PWM from APM output 0 while uploading new code

Posted by Bill Noyce on November 24, 2010 at 5:48am

Hi,

Has anyone else experienced a motor spinning up ( or a servo glitching ) whileuploading new code to the APM

I totally understand that while code is being uploaded the system is in aunknown state so i should expect the un-expected from the APM outputs and thatthe idea setup would be with all APM outputs disconnected while uploading newcode, but this is not always practical, particularly in the field while wantingto test various code versions.

I have purchase a 4-way switch to isolate the ESCs signal wires while uploadingcode.

Part of the reason for this post was to a) see if anyone has had thisexperience and b) get a warning put on the wiki because this random behaviourcould end up hurting someone. Nearly gave me a heart attack the first time itoccurred ;-)

Bill

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Replies

Developer

Mark Colwell November 27, 2010 at 12:01pm

This is happening for my APM beta, I have both digital and analog servos powered through USB port, I just thought it was undefined states during upload as I have no interference. I disconnect all servos when loading programs. ( I have stripped gears when testing with old AP). I am using a servo tester to drive Ch-7 for Mode control. I will be testing Turnigy 9x system soon so I can select any of 6 modes vs 3. and slew pan & tilt too.
Developer

Doug Weibel November 26, 2010 at 6:47pm

There is a way around this issue: If you have your transmitter turned on, are using channel 8 for mode selection, and have the transmitter configured to give you a PWM pulsewidth > 1750 (IE you are in "hardware" manual mode), then channels 1-4 will not be affected by the undefined state of the main processor while reprogramming. You could still get some glitching on channels 5-8 outputs if you are using those....
Mitch Robbins November 26, 2010 at 6:20am

I haven't had it happen on APM but have had it on several other custom and commercial boards. I simply assume servo and esc movement will be unpredictable and plan accordingly. A quad or heli inadvertently powering up on the bench or in your hand will definitely get your attention and make you think about it for next time!
Uwe Gartmann November 24, 2010 at 12:26pm

I use a 8 channel optocoupler device to separate APM and receiver from the other gear. The ESC delivers power for Servos. The APM is powered by a 2S lipo and a standalone UBEC from Castle Creation. I would never connect Servos directly to the APM because servos can make much noise on the power line. Remember, there sensitive sensor on the IMU. Stable power means more stable values from this devices.