Problem with MambaMax/Feigao 8L

I have an e-savage with a mamba max and feigao 8L running on 14 cells (4500mah elites). It had been perfectly fine for 10, maybe 15 runs. Well, not perfect, I melted 3 spurs and snapped 2 driveshafts, but thats another story.

It was going good when in the middle of a run it wouldnt start up after it came to a stop. It was all jerky, like it was out of radio range, which it wasnt. It was like it didnt have enough power to get rolling. If I picked it up it ran fine with the wheels off the ground. It also ran fine if I pushed it with my foot to get it going. I check the spur and pinion, they are fine. The drivetrain has no binds. The esc and motor were both very hot, hotter than normal. I thought it was a heat thing, or maybe a battery thing. I tried it once it was fully cool on 2 different sets of batteries and it did the same thing.

I just tried out the mamba with a 540 brushed motor on 7 cells. It wasnt in a car (dont have any more atm), just on the ground, but I ran it awhile and while the motor qot quite warm, as I expected, the esc didnt change temps at all. Which leads me to believe that it is the motor, althought I did check the leads and they are not broken. I dont know how else to test and dont have a hobby shop near me, and the ones I do go to occasionally dont know that much about brushless. I figured this would be the best place to get some answers. Let me know what you guys think.

[BrianG]

Welcome to the forums!

It's possible that the motor got too hot and weakened/nullified the magnets. Without a magnetic field, the motor won't turn. I recently blew a 10XL by using a center diff that unloaded the front end too much effectively running the motor somewhat unloaded. Running a motor unloaded gets them hot quickly. Too long and they get too hot and ruin magnets.

Also, 14 cells on an 8L is running quite fast (51k rpm). The general rule of thumb is to keep those motors at about 35k rpm or they'll get hot faster.

Besides, an L motor is considered a bit small to run something as heavy as a savage. You might want to try an XL motor and maybe gear up a little to compensate for the loss in motor rpm.

Thanks for the quick reply. Im on the e-savage.com forums, and a buncha guys over there run the same setup with no problems. Keep in mind this is an e-savage, not a GP savage, so 1/10th vs 1/8th scale. Its pretty heavy, but not as bad as a savage. Wheels/Tires are light too. Itll hit 45+ mph, which is ridiculous. Its too fast for that thing. I lowered it an inch, with some velocity offsets too, and its still squirrley at top speed. Its still impressive for just having 1 speed though. XL motors are too long Im pretty sure (its that or they have too large a diameter) but they dont fit well on an esavage. Gotta dremel the TVPs I think, maybe more, didnt want to go that route.

I dont recall for sure, but I dont remember it being overly hot when it quit working, it just heated up fast when I tested it later. Would you say it is more likely that it is the motor and not the esc? If it needs replaced (Im assuming its not repairable?) I will probably go with a 9L to keep the temps down a bit more. Any other tests I could possibly do?

[BrianG]

Oh, when I see "e-anything", I think it's a conversion. Sorry. :)

Well, the ESC ran the brushed motor with no issue. That doesn't mean the ESC isn't bad since there is a phase that isn't used when you go brushed, but at least the outputs on the red and black wires are OK.

Running the motor to 51k rpm is above the generally accepted 35k "rule". Above that, the motor doesn't run as efficiently and gets hotter for nothing. Actually an 11L would be in the right rpm range. If that isn't fast enough, you could gear up a little to compensate.

You could run it slow for a while and see what gets hot. The motors aren't generally repairable (or at least not worth the cost to do so). And, the S, L, and XL motors are all the same diameter, it's the length that's different.