Need some help: Fully custom build was fine, now having throttle range issues
I have a Savage .21 that I converted to electric using Kershaw direct drive, brushless motor, and 6S ESC and battery setup.
The truck was running perfectly for about a year since the build, then it sat for a couple months and now has this issue that I've been troubleshooting for a while.
When I first plug in and turn on the truck everything seems fine. FWD and REV are fine and I seem to have full power. Then within the first 5-10 seconds of runtime the max throttle output clearly starts being reduced. Then within 10-15 seconds the throttle only produces motion when the first 25% of the throttle travel is used. After that point on the throttle it is like the ESC prevents current from passing. It doesn't shut off. It just doesn't go. Doesn't make any sound.
Then slowly the throttle becomes less and less effective until the truck just won't go at all, at any throttle amount.
If I let the truck sit for a moment, it will go again, but the behavior resumes very quickly. And it is always progressive.
If I unplug and restart then the whole process starts over again, beginning with full power output.
I've been messing with this for a year trying to trace the cause. I've basically rebuilt the truck and still the issue persists!
I even use this radio for multiple vehicles so it shouldn't be the radio as it works fine in other cars and bikes.
I'm at a total loss and could really use some advice. I've been into r/c for decades and consider myself skilled, being able to fix 99% of what comes along. But this has me totally stumped.
As far as I can tell the direct drive is fine. Clutch is fine, alignment is fine, and everything turns as smooth and precisely as the day I installed it.
I've swapped motors (the original Medusa and a new CC, ESC's (both Mamba Monster), BECs (all 6V ParkBEC), and batteries (all MaxAmps 6S (2 x 3S).
Nothing is binding in the mechanicals. The ESC is programming fine. The motor seems strong. And the wiring is correct.
What could be causing this? I've replaced ALL the electrics. I thought surely that would fix it even if I never discovered the root cause, but no. Please help!
Thanks!