What just happened?
 

I had an odd WTF moment on saturday...

1/10 buggy
trinity 10.5 motor
MMP esc, internal BEC bypassed since forever.
frsky TFR4 reciver
bluebird 661 servo
old AMB transponder

20* endbell timing
45* boost, 20k end RPM
15/87 gearing

I've been running this exact setup for a few weeks.


Problem:
Before my race I turned the buggy on, checked the servo, throttled it up. The motor spun up, cogged and everything went dead.

The internal circuitry on the servo are charred remains of silicon. The RX is 100% dead. the AMB works. The esc/motor work fine.

Any ideas?:neutral:

Did you have battery voltage to rx and servo?

Something shorted by the sound of it.

Yes. The internal BEC of the MMP is bypassed to run full lipo voltage.

Are the servo and receiver rated for 8.4v?

The RX is rated for 10v.
the servo, Not technically, but I've used them for 2-3 years on 8.4v...

Agreed but a dead short skill causes a lot of current through everything.

Condensation perhaps, inside the servo/rx?...

Indoor carpet track...

What I mean is, when you take something from a cold place, to a warm one ( or vice versa ), the fairly sudden change in temp can cause condensation to form- that's why they say to let electronic goods sit for a while before powering them up when moving them from say, the loft/attic to your living room etc.

Prolonged over-voltage seems to be the more likely cause though, it does shorten the life span rapidly & it just seems to have let go this last power-up...

It was indoors for 10+hrs... It blew up 3rd round of qualifying.:neutral:

As neil stated in his second sentence, prolonged over voltage on that servo probably made it let the smoke out. The servo burned, then shorted and took the rx with it.

I've had several standard servos (not hv) work well on lipo 8.4v, and some of the same model have burned almost immediately.

It's a risk you take in over volting anything.

Time to get an hv servo.

Sounds like servo failed, shorted, sent excess current to Rx and shorted that too. Could be the other way around as well.