How to fry Goat!

[RPP Jim]

Read my e-mail below for the whole story...

-----Original Message-----
To: Technical Support
Subject: Failed Goat ESC

Let me start by saying I don't expect this failure to be covered under warranty. One, I bought it secondhand on eBay (described as new, but no guarantee). Two, I was using an 8-cell 1600mah NiMH saddle pack. I know the manual says the ESC is designed for 6-7 cells.

That being said, I thought I'd share the failure. My crawler is an Axial Scorpion with your Goat ESC (with Novak fan) powering a 55T Axial motor. I have a Spektrum DX6 radio with AR6000 receiver. The steering servo is a digital titanium Hitec HS-7955TG.

I was crawling last night for maybe 15 minutes. I switched the receiver off and was carrying my crawler a few hundred feet back to my car. As I was carrying it, I was talking to a few people and fidgeting with the front wheels, making the steering servo go back and forth. As I was talking, someone said "whoa!" and I looked down to see smoke coming from the saddle pack. I immediately disconnected the pack.

I thought the saddle pack had failed and when I got home, I connected a new 7.4V 2S lipo to test the crawler. Bad idea! Whatever happened to the ESC had created a short (this is why the saddle pack got so hot) and when I connected the fresh lipo the ESC shot smoke out the side and one of the motor wires desoldered itself!

Is there a chance that the servo acted as a generator and fed power back through the system? Or, was it the 8-cell saddle pack that killed the ESC?

I have attached pics of the saddlepack and the failed ESC. I thought you guys might learn something form the failure.

If I buy another Goat, I will only use a 6 or 7 cell saddle pack or a 2S lipo as your manual states.

-Jim

RESPONSE FROM NOVAK TECH SUPPORT:

Dear Jim,

Thank you for the email and the pictures describing your failure.

We are farmilliar with this type of failure and we have made modifications to our ESCs to prevent this sort of thing from happening in the future with these updated units and with future designs.

The failure occurs pretty much exactly as you describes: The motor inside the servo generates voltage which can cause the transistors inside to "float" ... when they are not connected to a battery nothing really happens, but if the ESC is connected to a battery, power can flow through these transistors and cause shorts which lead to the failure of the ESC.

Even though future units are better protected from this type of failure, it is always a good idea to unplug the battery from your vehicle after you are done running it and never leave it plugged in while in transport or storage.

You can return the ESC to us and have it replaced out of warranty. The non-warranty replacement cost on a Goat ESC is $49.

I commend Novak for offering a non-warranty replacement for goofy mistakes like mine.

I hope this posting helps anyone else who likes to fidget with their front wheels. Just make sure if you do, the battery pack it disconnected!!!

-Jim


Desoldered itself! That's a 14 AWG wire to the motor.


Ouch!!!


HOT saddle pack.

[moes670]

Hmmm interesting! Getting mine back on Monday. Same thing plugged in the battery right before a comp set my rig down to hand in my score sheet looked down and smoke was rolling out my rig. Lipo was hot and heatshrink was melted on one end. Plugged in a new battery and same thing. Dont remember moving the wheels back and forth but anything is possible..

Maybe it would be a good idea to just eliminate the on off switch. That or never turn it off just unplug the battery to shut down your rig........

have to see if there is an explanation as why mine failed in the box when I get it....

[the kil]

jim i think its time for a FXR and a 3S, leave the slow goat behind :-P

[BigB_117]

woah that thing really got cooked.

Jim didn't you just say on Sunday that you wanted to go to a 3s lipo for more wheelspeed?