Big Rock Cogging/no motor response @ 12+volts , servo fine

[Rottster]

Hey all, my Big Rock has been acting weird lately meaning no forward or reverse once battery pack voltage drops below about 12.3 to 12.2V. The servo works fine and the motor is cool, barely warm to the touch. If I reset the ESC (power switch) it runs for about minute or two just fine, then dies. Any ideas? Has the esc bit the dust?

 

[jkflow]

Check your wires between ESC and motor, most likely a bullet came loose.

 

[Rottster]

Check your wires between ESC and motor, most likely a bullet came loose.

Tried two batteries and the connectors are dang near antiseptic. No heat on the connectors either which would be a dead giveaway.

 

[N.Mango]

Just because I had it happen to me...
Mine was a faulty servo but you would have never known it was the servo because it worked perfectly fine.
Tried a different servo and all was good so tried the original one again and same issue.
Tossed the original and kept using the new servo with no issues after that.

 

[jkflow]

Could you take a Pic of the setup?

When I had a desoldered bullet it wasn't visible.
Could you try a different motor?

 

[SrC]

If you are running the stocker servo, that needs an upgrade anyway. Good chance, the Spektrum servo is to blame when under load and the rig's ESC is hard throttling. Hard to simulate this on the bench.
Many have seen this. It can even take out/brick your ESC.

 

[Rottster]

@SrC Yep, still running the stock ESC, motor and servo. I had picked up a 35 kg servo a few months earlier, I suppose it's time to install it and see if that's the issue. The symptoms sound about exactly what you stated and throttle would gag then stop working after a hard turn at the end of the run. Also, like you say, almost impossible to replicate on the bench. Hopefully the servo hasn't damaged the ESC or Hobbywing here I come.

 

[jkflow]

Simple check is to just disconnect the servo and see if your other issue disappears. I doubt it's the servo, but easier to disconnect than to go into details.

 

[Hector_Fisher]

I had a similar issue on my big rock. Lots of stuttering and cogging after the esc/motor warmed up when running. Got worse towards the end of the pack. Could even get the truck started without a shove with a foot.

Some ideas for trouble shooting:
-does the truck start going if you give it a push start and throttle?
-try running a cold truck on a half charged (storage charged) battery and see if the issue happens right away or still takes a bit to come around
-try a different battery
-swap out components one at a time, as suggested above, to isolate when a change happens
-give the truck a push and make sure it rolls smoothly.
-then remove the power module and center driveshaft and check that each diff rolls smoothly.

In my case, after i did tons of troubleshooting, i finally found out the ESC was bad. I got Horizon to warranty it and the problem went away.

Best of luck.

 

[Rottster]

I haven't had time to give the "Fat Rock" a hard run yet but I think I found the problem. I'll update this weekend with the resolution once I'm 100% positive.