I’ve seen some people experiencing problems with ESC not sync or motor stops and starts again and stops ( this was mine) and after a full week i finally found the issue. To be very clear … I’M TALKING ABOUT APM 2.6 2.8 , don’t know PX , never had one.
So I was experiencing this problem:
Esc connected to RC receiver -> motor spins fast and is very powerfull
ESC connected to OUTPUT3 throttle -> motor spins quite bad and i could stop motor with just a finger.
As every body knows motors are generating noise while they spin. This noise will affect your PWM signal that comes out from APM 2.6 2.8 heading to ESC, and depending what ESC you use it will affect more or less the rotation of your motor.
First ESC i used … was just a nightmare … it was spining like a old grandma on the dance floor. :))
Second ESC i used was a bit better but still had a bit of grandma behavior …
So i’ve put the oscilloscope on the pwm signal OUTPUT 3. It was looking bad … very bad , a lot of noise arround signal lines ( are not called like this but 'm not English native). So what i’ve done is inspecting APM hardware … Each output pin comes through a 221 (220 ohms) resistor from microcontroller. Hold on a second … no supression ? … No RC filter supression… Inspected the RC receiver and i can say the receivers have a RC filter. Each pins have a 470 ohms and 0.1 uF RC filter.
So i was like … let’s add a RC filter to APM 2.8 output. Guess what? IT WORKS! ****** FIREWORKS**** :))
BELOW is all you need to do if you have the same problem.
220 Ohms and not 470 ohms because apm already have a 220 ohms resistor on each output … Rt= R1 + R2 series. Normally you should add 250 ohms but because the only resistor i had arround this value was 220ohms i used 220ohms.
I glad that your figure out your problem !
Did you have the reference of bad esc? I think that recent esc are opto-isolated to prevent this kind of problem
1st one was X -Car-35a
2ns one is a ESC home made using infineon tehnology schematic for BTN8962TA. Just modified it a bit to make it work with PIC microcontroller.
I don’t think the ESCs have any opto isolators… as the RC receivers already have plus those filtees must be calculated and just adding more and more filters in the end your pwm signals will be again disturbed.
The issue is very clear … input signal APM has rc filter from rc receiver so all your pwm going into atmega and processed are good signals…
The problem is that the outputs are coming out from atmega without any rc filters… just a 220 ohms . Should be 470 ohms and 0.1uf cap grounded. The atmega is sending good signals out but… those signals get disturbed on their way to the ESC… so add rc filter.
Also Bat - and Bat + from ESC must be twisted and Mot- and Mot + must be twisted arround 6 times per foot…
If there is somebody that still have issues after adding RC filter… increase the resistance in 10 ohms at a time.
I suspect your APM is a cheap clone and the build quality isn’t great. Its not surprising as you can’t get original manufactured ones any more. Its one of the reasons people move to the latest hardware if they have a new project so they know the build quality like that of the CUBE - http://ardupilot.org/copter/docs/common-pixhawk2-overview.html - is reputable.
You did well to identify the problem and we appreciate you posting it here for others to see as well. This could help a few people out.
Grant… clones vs gnuine apms have same schematic. this rc filter is missed as the designers thought that is not necessary because rc receivers already have. It is necessary especialy if brushed motors are used. anyway… my project fully works now. :))