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Old 11-10-2008, 11:21 PM   #1
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Default Gearing woes

Alright well I've been dealing with pretty high temps 180-200 on my mamba 6900kv in my B44. I'm running a 16/84 and I can't seem to get the temps down, I don't feel like buying motors left and right. It seems like my temps jump when I try to run a 18-19t pinion (stock).

I do understand that the mamba's can run hot but 200 for a motor will kill it. The track I run at is a 100'x50' indoor dirt track with full throttle for a 1 second on the front stretch, nowhere else. Traction is usually pretty high, its packed dirt (feels like cement sometimes). Either way I can't touch the ESC (mamba max) or motor for more than a second after a 5 minute heat. What should I do with the pinion? Lower? You can hear it spool up 1/2 way down the front stretch. I know it's a lot of motor for the B44 but it's what I have to work with. I have cut large vent holes right above the ESC/Motor in the past but it still ran 190.


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Old 11-10-2008, 11:26 PM   #2
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I would try to dial in your esc. Make sure it's not turned up too high.
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Old 11-10-2008, 11:55 PM   #3
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Yeah from what I read, that motor is designed more for on-road use - smaller wheels, small pinion and large spur. It's also drawing a lot of power through the ESC (making it hot) and being on and off the throttle a lot on that track is all combining to make the motor hot. You're gonna have to gear it conservatively to keep the temperatures in check but with the sound of that track, you want torque over top speed anyway...so it's not a big issue. I think one of the locals at my track runs a B44 with a 4600kv Mamba in it, if memory serves. So basically I think you put an on-road motor in an off-road car
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Old 11-11-2008, 07:43 AM   #4
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Is there a cooling fan on the ESC? How about putting one on the motor?
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Old 11-11-2008, 07:45 AM   #5
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Check to be sure nothing is binding as well. That can cause excessive heat. Pull out the motor (or at least the pinion) and see that everything is spinning freely.
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Old 11-11-2008, 07:47 AM   #6
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Quote:
Originally Posted by dr_hfuhuhurr View Post
Check to be sure nothing is binding as well. That can cause excessive heat. Pull out the motor (or at least the pinion) and see that everything is spinning freely.
Also check that the pinion/spur mesh is not too tight! This can elevate your motor temps.
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Old 11-11-2008, 10:49 AM   #7
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I would put a heat sink on your motor and open up the body for more air circulation. I think the problem is the heat can't get out of the body.

The other thing you might want to consider for the ESC is how much you are able to pull full throttle. if you are never able to get to top speed on the track, you need to gear down. part throttle puts more strain on the ESC I believe.
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Old 11-11-2008, 10:54 AM   #8
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have you tryed differnet gearing?
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Old 11-12-2008, 04:26 AM   #9
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I tried gearing up to 19t and inbetween but the motor only got hotter. Debating whether or not to get a 15t, I'm running a 16t/84t and it's still pretty toasty
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Old 11-12-2008, 05:04 AM   #10
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Stock gearing with the Mamba? heck no. You have to gear down. 15T or 16T is the way to go here. Consider "stock". That's with a motor like 12T to 10T. The manual suggests 19/84 for a 10T brushed and same for 6.5T brushless. those are starting numbers.

Let's look at the #s. 6900 motor at 7.2V = 49000RPM or more. stock motor of 10T brushed is a motor of about 37000RPM, so the mamba is capable of going about 25% faster RPM-wise. So, that's about 2-3T lower pinion gear. If you are not on full throttle much on the track - gearing down is the way to go. You want to be punchy out of turns and lower pinion is quicker along with lower motor temps. quick wins races too - vs. high top end. If you want more top-end, you'd want to do it with a lower kv motor and higher gearing (more torque).

Make sure all your bearings are smooth too and take any pinion/spur binding out of the equation. If stuck - ask other racers at your track to take a look. Once you hurt a brushless motor with high temps, the rotor may be starting to demagnetize and you could replace it to get a new rotor (which has the magnet in it) to freshen up the motor.
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Old 11-12-2008, 05:21 AM   #11
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There is no binding, thats for sure. I'll try a 15t since I can barely keep full throttle on the front stretch (due to the car spinning itself out). I will also cut a slot in the undertray under the motor. Thanks! I figured the mamba liked smaller pinions.
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Old 11-12-2008, 09:54 AM   #12
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Make sure your settings on the computer like Timing is set to the lowest setting possible. I had tons of heating issues when trying to use the higher timing settings.
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Old 11-14-2008, 12:09 PM   #13
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i see we are neighbors - both in MA! look at the setups chart - there's so many setups for t4, b4, and b44! if you need more help pm me- but do you homework first!
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