Pixhawk sending wrong PWM values to Wild Thumper

I have assembled the following:

6WD Wild Thumper
T’rex Motor Controller
Pixhawk Controller
RC Radio through a Spektrum Satellite Receiver

Each part on its own looks good.

APMrover2 code: 2.46
Skid_Steering_IN : 0
Skid_Steering_OUT: 1
Mode: Manual

Pixhawk Output Servo 1 direct to Left Motor on Trex ( actually irrelevant at this point)
Pixhawk Output Servo 3 direct to Right Motor on Trex ( actually irrelevant at this point)

I have recorded the PWM values coming out of the Pixhawk and I get the following:

Moving the stick clockwise:
1900 & 1064 Stick at 12 o’clock ( values going to Lmotor and Rmotor before bias to +/- 255)
1716 & 1065
1692 & 1065 Stick at 3 o’clock
1699 & 1065
1894 & 1065 Stick at 6 o’clock
1906 & 1065
1906 & 1065 Stick at 9 o’clock
1906 & 1065

I think my Radio is accurately calibrated with each channel giving values from 1050 > 1500 > 1950 microseconds.

Can someone suggest where to look. I have checked this thing fairly well but have missed something.

Needless to say, when powered up the wheels turn full speed on one side and almost nothing on the other.

The skid steering function in v2.46 does not work correctly and will cause incorrect operation of your rover.
Please fall back to version 2.45 or use v2.47 beta 1: http://firmware.diydrones.com/Rover/

Thanks for the heads up on 2.46.
I did try 2.45 and 2.47 beta and neither one solved my issue, They just changes the values very slightly.

I really need to find a way to watch values in the code on the fly. Do you know of any way to printf values out to my PC as the program is running. This would be on my own compiled 2.47 beta code.


You might want to put the right ESC input on the Pixhawk output channel 2 since output channel 3 is not moving at all from 1065us when you move the joystick around the clock.
When the stick is at 12 o’clock both steering outputs should be 1900us.
AT 3 o’clock the left output should be near 1900us and the right output should be near 1000us if your ESCs have reverse.
And so on.
You need to look at your RCMAP parameters since you are using a Spektrum Remote Receiver.
On my rovers, which use a Pixhawk and a Spektrum Remote Receiver, my default map looks like this
How you setup the RCMAP will affect your Pixhawk output channels.

Thanks for the idea. My channel map was identical to yours.
But it made me check other similar things.

Turns out that the 2 motor signals were coming out of the Pixhawk on servo pins 1 & 2; not 1 & 3. Any documentation on this??

Once I discovered that, the thing actually worked. All I needed to do was reverse the direction of channel #1 ( ailerons) so that it turned right instead of left.

One puzzling thing is the horrible hum coming from the motors when the stick is dead neutral. I expect I need to expand the dead zone value. Any ideas?

Jim Calvert

When a Remote Receiver is used in place of a standard receiver and PPM encoder, the channel inputs sequence is different and therefore the outputs are different as you can see.