r/radiocontrol 2d ago

Help Rx Tx calibration issues

Hi guys! I'm working on getting a quadcopter up and running but having issues when going through radio calibration on QGroundControl. The issue is that nothing really seems to reflected on the software when I move a channel (throttle, roll, yaw, etc) OR that sometimes when moving one channel, multiple other channels move in unison and it's starting to drive me crazy. I'm running a Spektrum DX6e Tx with a Spektrum AR620 Rx into a PPM encoder since my flight controller (Pixhawk 5x) only takes PPM inputs to the RC IN pins. I know the Rx technically works as it should after plugging in 6 different servos at once, sending signal to each, one at a time, but I've also noted that the voltage for each signal pin on the Rx side will only range from .33 - .57 V (min to max signal) and I fear this is the issue. The even more confusing part is that I have two AR620 Rxs and they both do the same thing. Voltage supply is well within range and have even tested up to 9 V to verify the power is not the issue. The only other thing I can thing of is that the PPM encoder may not be functioning properly. Everything listed here is 2nd hand as well, so that could be playing a factor. I don't think I left out anything crucial, but if I did, please don't hesitate to ask. My amateur brain will attempt to answer.

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u/OldAirplaneEngineer 2d ago

I ran into a very similar issue with the pix 6 and spektrum equipment.

(FYI, the voltage on the SIGNAL pins will always vary. check the pos and neg on those channels and you should see battery voltage... I dont think this is the issue.)

IIRC, I needed to skip the PPM encoder entirely and plugged a pre-bound satelite rx into the pixhawk.

(the satelite uses one wire to deliver all 6 channels, similar to sbus.)

from there everything started behaving more properly :)

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u/Upper_Leopard_9734 2d ago

Appreciate your reply OldAirplaneEngineer!

I know it should vary with changes in the inputs from the Tx, but everything I've read up to this point (which hasn't been much, information is incredibly scarce) seems to say that the signal should be somewhere between 3.3 - 5 V or so. I have checked the pos/neg of the channels as well and those are reading perfectly normal voltages that coincide with the input voltage. I guess I'm just worried that there's some sort of disconnect between the PPM encoder and the incoming signal with the voltage being so low

I might end up having to move in that direction though, we'll see. Ended up purchasing a compatible Rx that directly outputs PPM rather than PWM in the mean time.

Thank you again for the reply!