9xl and heat
 

I got a revo with an emaxx tranny on it geared 14/64 and stuck in 2nd. It's got the stock diffs and 40 series tires. I'm running a 9xl with 18 cells and after about 6mins of running, the motor is too hot to touch for more than a second. The 9920 and batteries are barely warm at all. Do these motors run this hot without a heatsink, or is my gearing all wrong.

Id try running a higher spur if possible, like a 72 t or a lower pinion, like a 12t, that should bring the heat down.

Wrong, sylvester. I think you have it way undergeared, slow-stampede. Get a bigger pinion!

Sounds like undergearing to me, too.

Although not always true, a rule of thumb is:
Hot motor, cool controller, cool batteries = undergeared
Cool motor, hot controller, hot batteries = overgeared
Warm motor, warm controller, warm batteries = happy components :)

Hot, warm, and cool vary as well, so here's another general rule:
Hot for a motor = generally over 160F
Hot for a controller = generally over 150F (or "thermal" range for the controller)
Hot for batteries = generally over 150F for nimh, 130F for lipo
Warm for a motor = generally 100F through 150F
Warm for a controller = generally 100F through 130F
Warm for batteries = generally 100F through 130F for nimh, ambient temp through 120F for lipo
Cool for all components = generally ambient temp and up to 10 degrees F more

The reasons the above are not always true are numerous, but may include:
Sticky drivetrain - will put un-necessary strain on electronics whether geared correctly or not.
Poor quality batteries - batteries will heat up regardless of gearing.
Wrong motor for the application - will put un-necessary strain on electronics whether geared correctly or not.
Wrong controller for the application - will put un-necessary strain on electronics whether geared correctly or not.

The list goes on, but this can give you an idea of things to watch for.

Edited to add the following:
Please note that this information applies to the sensorless brushless systems typically found here at RC-Monster.com (BK Warrior/Micro controllers, MGM controllers, BK motors, Lehner motors, Feigao motors). These rules do not apply to brushed systems or other brushless systems, at least not in the same ways.

Wow, that's a nice compilation of data for newbies like me! Thanks, even though it wasn't specifically for me! It all makes sense when you think about it really (from an electronics perspective), but it's nice to have the list. :)

Great info guys....I had a feeling it was undergeared from reading all the other forums. I'll have to get a smaller spurr since that's cheaper than a bigger pinion :D I'll try 4-5 teeth smaller and see what happens.

I like to run my 9xl around stock gearing 18 66 or so. I have ran it with a 20 51 gearing. The motor was warm and the esc heated up. but it was fast
.