PPM Problems (V=3.5V, 4 of 8 channels)

APM planner tells me the RC is not turned on and I see nothing on the slider bars.
This is for a RaspberryPi2 with the latest EMLID image (20160212) for the Navio2.

PPM encoder seems to be working, scope shows 0 to 3.5v pulses. For the 4 channels connected the 4 pulse widths change with stick movement (0 - 12ms within the frame). I have a large “blank” space (12ms to 25ms) where the encoder is obviously expecting input channels 5-8. Is this the problem? Or should it be a 5V output?

@hedgey 3.5V is okay, but the decoder expects 8 pulses and a sync pause, so that’s probably the case. What encoder do you use?

Encoder is this one:

How long does the sync pause need to be. Total frame is 25ms. 1-8 channels are in 0 to 15ms (roughly). 15 to 25ms is constant at 3.5V.


As far as I remember it has to be no less than 4ms.
Could you please post a picture of the signal as seen on the scope?

BTW the ESCs are not connected yet.Could that be the problem?

No, even without ESCs you should see bars moving in Radio calibration.

Could you please post a close-up picture of how everything is connected?
Also, can you check output channels with the scope? What’s going on there?

0V on PWM outputs (ch14)

Is there anything on channels 1-4?

Nothing on any channel

Could you please run the following command and post its output:
cat /sys/kernel/rcio/status/alive



cd /sys/kernel/rcio/rcin
sudo cat connected

Then ls. This is where you’ll see the channels. You can look into your problem a little bit by moving sticks and checking if the values you see in the directory you just issued you command in, do match. I’d be very surprised if they don’t.

What version of APM do you run?

Yep, values changing correctly from 1007 to 1994.
Channels 7 and 8 are constant at 1500.

APM version v2.0.18 on Windows 10 (also tried Mint with same problem)

Seems like hardware-wise your Navio2 is alright.
Could you please try Mission Planner?


And could you also say what version of ArduCopter is being run? Is it from the latest debian package?

Mission planner is forcing me to upgrade firmware? I assume that won’t work?

Installed whatever version was linked to on your page yesterday.
New link has an error on install:
“trying to overwrite ‘/opt/apm/bin/ArduCopter-hexa’, which is also in package apm 3.3”


No, firmware update from MP is not suitable for Navio.

To install the package try adding force option:
sudo dpkg -f install apm-navio2.deb

dpkg not liking the options. Should it be something like (but this doesn’t work either):

sudo dpkg -i --force apm-navio2.deb

Yeah, sorry, the command above is incorrect.

Please try:
sudo dpkg --force-all -i apm-navio2.deb