Power up the PixHawk and a Trax ESC

I have a Trax Slasher, Trax ESC, PixHawk, and the 3DR power module. When I first power up the system by plugging the battery cables together, the PixHawk starts booting. Then I press the start button on the ESC and the PixHawk gets stunned and stops working. I hear a clicking noise from the buzzer and that’s it. But if I hold down the ESC button first and then connect the battery cables, then release the button after a second, everything starts up as expected.

I’m assuming when the ESC starts up, there’s a current surge which drops the voltage going to the PixHawk and stuns it. Any ideas on how to fix this?

@dksmall,
I had a similar problem during early Pixhawk testing on a Traxxas brushless 4WD Slash.
The Pixhawk servo output bus power bus (which acts as a secondary power supply for the Pixhawk if the primary power supply fails) is supposed to tolerate ESC BEC input voltages of greater than 5.5 vdc. The Traxxas ESC BEC is 6 vdc and not 5 vdc.
If I booted up the Pixhawk and received the green LED I would then start the Traxxas ESC only to have the Pixhawk occasionally go into reset and run wild causing the Traxxas to run full forward or full reverse.
The solution was to not power the Pixhawk servo power bus from the Traxxas ESC BEC and power the steering servo directly from the ESC BEC bypassing the Pixhawk power bus.
Regards,
TCIII AVD

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I removed the Esc power from the output rail and it’s only connected to the steering servo and the receiver. Now when push the Esc button it still resets the PixHawk, but it does boot up again, rather then being stunned.

@dksmall,
You should let the Pixhawk power the R/C Receiver and not the ESC BEC. That may be where your problem is.
Regards,
TCIII AVD

From where on the PixHawk? There’s no voltage on the center pin of the servo outputs.

@dksmall,
Normally the Pixhawk receives a R/C receiver’s output from one of two ways: the Spektrum Satellite Receiver input or the PPM input on the left side of the Servo Output Bus. The PPM input accepts inputs from a PPM Encoder or the newer R/C receivers that have a PPM serial output. The PPM input will supply power to the R/C receiver or the PPM Encoder whichever is attached.
In the Rover Wiki:
Connect remote control inputs

Pixhawk is compatible with PPM remote control (RC) receivers, Futaba S.Bus receivers, and Spektrum DSM,DSM2, and DSM-X Satellite receivers. For traditional single-wire-per-channel (PWM) receivers a PPM encoder can be used to convert the receiver outputs to PPM-SUM. Information about compatible receivers and how they are connected can be found in Compatible RC Transmitter and Receiver Systems (Pixhawk/PX4)
Regards,
TCIII AVD

I see. I had measured the voltage one on the RC outputs on the servo connector, didn’t think about checking the PPM input. I’m using S.bus so I’ll try using a full 3-wire cable between the PixHawk and receiver.

Had a rover crash so it’s awhile before I could change the wiring. Powering the receiver from the PixHawk didn’t change anything. Anytime I turn on the Esc, the PixHawk resets. Shouldn’t be a big deal since that’s part of my startup sequence. If I ever get the rover on a scope I’ll see if there’s a power drop on the output of the power module.

@TCIII

The solution was to not power the Pixhawk servo power bus from the Traxxas ESC BEC and power the steering servo directly from the ESC BEC bypassing the Pixhawk power bus.

I am struggling to visualise how I would do this. Do you have a build log/photos or more details you could share please? I have looked through your other posts but I can’t find anything.

Many thanks,
Andy

@AndyEG,
The process:

  1. Remove the red wire from the ESC servo connector.
  2. Remove the red wire from the Steering servo connector.
  3. Connect the two red wires together which will provide ESC BEC power (+6 vdc) directly to the Steering Servo bypassing the Pixhawk servo output power bus.
    Regards,
    TCIII AVD
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Many thanks @TCIII. That makes perfect sense now!

Best,
Andy