I am trying to setup a Traxxas Slash Platinum with my Pixhawk. It works fine for a bit but will randomly stop working. I look at the pixhawk the FMU power light is off. If i turn off the traxxas VXL-3s ESC the FMU will then light up and everything will work fine for a while again.
I am using the 3D Robotics power module and a 5000mah 2s LiPo. I changed the connectors on the power module to traxxas connectors.
Any suggestions would be greatly appreciated. I have also attached a log from the microSD card of one of the failures.
@Keebie81,
I had the same problem on my Pixhawk powered brushless Traxxas Slash.
The solution was to not power the Pixhawk Servo Output power bus with the ESC BEC.
I use the ESC BEC to power the steering servo directly and not though the Servo Output power bus.
Apparently there is some kind of conflict between the PM and the ESC BEC when the BEC is used to power the Servo Output power bus that has yet to be resolved. The Traxxas ESC BEC puts out 6vdc and the Pixhawk power management function is supposed to handle Servo Output power bus input voltages of up to 10vdc, but based on mine and your experiences I do not believe that to be true.
When I originally had the problem, I suffered two runaways one forward and one in reverse because the OI went wild with the loss of the FMU.
Regards,
TCIII ArduRover2 Developer
@TCIII
Thanks for explaining it. So if i understand correctly, i should have the power and ground from the esc cable go to the same on the servo. And only have the signal cable for each going to the pixhawk.
@StefanG
I am not using the zener diode. I just have the pixhawk powered from the power module.
[quote=“Keebie81”]@TCIII
Thanks for explaining it. So if i understand correctly, i should have the power and ground from the esc cable go to the same on the servo. And only have the signal cable for each going to the pixhawk.[/quote]
Close. I pulled the power pin from the ESC three pin servo connector and connected it directly to the power pin on the steering servo connector. I left the servo signal and ground pins connected to the Pixhawk Servo Output channel connectors for the throttle and the steering servo. The Pixhawk Servo Output power bus serves as a common ground for both the Pixhawk and the ESC/Steering servo when connected in this configuration.
Regards,
TCIII ArduRover2 Developer
[quote=“Keebie81”]@StefanG
I am not using the zener diode. I just have the pixhawk powered from the power module.[/quote]
The problem you are describing sounds somewhat familiar. It does occur not seldomly when the PH has “double power”. The Zener-diode should prevent this and if your BEC is 5V it can even be used as failover power supply in case the PM burns out.
You must in any case also connect ground to the PH. Especially from the ESC this is important! From the servo it’s still better and you might see some jitter if you don’t.
@StefanG,
I was running the BEC output of my Traxxas Slash ESC into the Pixhawk Servo power bus and powering both the servo and the Pixhawk with that BEC and the PM for a dual supply configuration.
I had two runaways with my Slash, one in the forward direction and one in the reverse direction at full speed when the FMU shutdown and the IO randomly went to either full reverse or full forward.
Tridge added code to the IO to put the Servo Outputs at 1500us (neutral for a rover) if the FMU shuts down.
The Traxxas ESC BEC supplies 6vdc and I believe that the Pixhawk dual power management does not like the 6vdc input on the Servo Output power rail and will randomly shut the FMU down.
There was much discussion about this issue on the drones discussion Group, but nothing ever became of it as to what caused the FMU to shutdown.
The IO is supposed to be able to handle up to a 10vdc input on the Servo Output power bus rails.
Since I changed to powering the rover steering servo directly from the BEC and not going through the Servo Output power bus rail, I have never had the FMU shutdown again.
Safe is better than a runaway at full speed until this issue ever gets resolved.
@TCIII:
As far as I understand it, the Zener Diode is supposed to fix that problem by regulating the voltage across the low power servo rail to 5.6V. There was some discussion about that in the dev call on Feb 24.
But of course you are right that safety comes first!
@StefanG,
I may have smoked my Developer Pixhawk because at the time I did not realize that Traxxas ESC BEC was supplying 6.0vdc and that Pixhawk was the one that had the runaways due to the FMU shutting down.
I have not used it since the runaways and purchased my own Pixhawk to use in its place.
I guess that I need to try the Developer Pixhawk again, but just power it with the PM to see if it still functions.
Regards,
TCIII ArduRover2 Developer
I was able to make the changes today. I have the power wire from the esc wired to the servo. Ground and signal for both connected to pixhawk. I still had two times when the pixhawk restarted itself, but the fmu light was green. I just had to re-arm and it then worked.