Erratic motors when using RCPassThru

Hi there

I’ve been trying to use CH8 in PassThru mode (to check out undercarriage motors). As soon as I click Write Parameters in Mission Planner after changing RC8_FUNCTION the motors move randomly in jerky motions.

The chout numbers in Mission Planner are dead stable. Navio2 outputs for ch8(top) and ch4 look like

Any thoughts much appreciated, but looks rather like a Navio PWM generation issue

FrSky X9D tx
FrSky XSR rx


By motors you mean servos? If so, then the issue is that they are not 400Hz PWM compatible. We are working on an update for Navio2 that will allow 50Hz output on 10ch-14ch, that should be ready in about 2 weeks.

PWM on your scope looks fine.

Sorry, I haven’t explained myself very well. I’m building a quad copter so when I said “motor” I meant the prop motors/esc, and the undercarriage is, as you say, a servo.

I now understand that the undercarriage servo may not be impressed with a 400Hz input - thanks for that, I’m on a very steep learning curve!!

However my original point was that the prop motors moved erratically when CH8 was enabled, and I assumed that was related to the PWM signal from the Navio2 having pulses missing (photo in previous post).

As soon as CH8 is disabled, the signals appear “normal” (photo below) with no pulses missing.

Am I still imagining a problem? : )



I have missed the passthrough part, this issue has been previously reported here: Motor/ESC problems with RC passthrough enabled
It is related to the passthrough mode only.

This will be fixed. We are currently focused on bringing out a new image that will support Rpi2/3 Navio+/2 and auto updates. After that we will get back to this issue and the one related to servo frequency.

Thanks Igor, apologies for the duplication

I’ll go back to getting my project into the air!


No need for apologies :slight_smile: Thanks for the report, I completely understand that it was hard to find in the forums.

Best luck with your project!

Hello Igor,

Any update on this issue? I have the latest 3.4-rc1-20160609 and the exact same problems with rc passthru. I would need this fixed quite urgently.

Have you sudo apt-get update && sudo apt-get dist-upgrade? This should help.

Hello George,

yes I have done that. To be on the safe side, I even started from scratch using the emlid image, then

sudo apt-get update && sudo apt-get dist-upgrade

sudo apt-get update && sudo apt-get install apm-navio2

Same problem. Has this been addressed?