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?

Your servo fried, and possibly back-fed into the RX and took it out also.

But why...

Vibration and jolts from landings wreak havoc on any electronics. Over time it takes its toll and they will eventually fail. How old is your equipment?

Internal BEC bypassed, are you using an external BEC or running direct battery voltage? If direct is the servo rated for that?

lipo voltage and yes.

Lipo voltage direct is going to be at least 7.4v - that servo shows no listed specs over 6.0v (standard BEC voltage) and it would be rare for an "HV" servo not to list a 7.4v spec if it could do it. I would double-check that before ordering a replacement.

Is it this one?

He has been running the 661 & the 617 successfully at 8.4v for a few years now.
Yeah, BlueBird doesn't rate them above 6.0v...
I personally don't run mine above 6.0v.

So what may be the cause is the driver cir of the servo back fed 8.4+/- on the signal wire????

The other theory in my mind was back EMF from the cogging, but I didn't see what came first, the runaway/cog on startup or a rev-up & loose sensor wire that caused a cog & then the runaway.

Have to ohm out the toasted servo board & see if there is a fused connection...

We have had great success with those particular servos for a few years & this has been the first catastrophic failure/fireball.

At least it's not a traxxas servo...

At least you still have the esc and motor. I lost both when my Tekin motor went out and took the Tekin esc with it, don't feel bad.

Dang! There is pieces of the board outside the case