Motor heat - which way do I go with the gearing?

[VintageMA]

Setup: XB8EC geared 14/48 w/ 1512 2.5d (2050kv) on Neu 3900 5S. (Geared for about 40-43mph).

Great setup, but temps at the end of 15 very hard minutes:
-Battery - 100*
-ESC (mm w/fan) - 130*
-motor - 158*

Average current ~14amps, according to Watts-Up meter max current 72A.

I went from 17/48 @ 4S to 14/48 when i moved up a cell to 5S.

Most threads here show cool batteries, cool/warm esc, hot motor = undergared.

I am not sure if that is the case or not, so looking for some input on the gearing direction people feel I should go. Am I trying to hard with the motor or not putting enough load on it?

Which way do i go the get motor temps down? 13/48 or 15/48.

Thx.

The idea behind undergearing generating more heat in the motor is that the motor is running near max RPM all the time since you'd be on full throttle more to get the speed you need with lower gearing. You can tell best if you feel you are on full throttle most of the time. If not, then gearing up probably will not make much difference. If it were me, I would get both a 13 and 15, so i could try them both.

J.

[lutach]

Originally Posted by 83gt

The idea behind undergearing generating more heat in the motor is that the motor is running near max RPM all the time since you'd be on full throttle more to get the speed you need with lower gearing. You can tell best if you feel you are on full throttle most of the time. If not, then gearing up probably will not make much difference. If it were me, I would get both a 13 and 15, so i could try them both.

J.

That's what I would do. I don't think 158F is that high though.

So if you motor is warm do you want to go to a smaller or larger pinion?

[VintageMA]

I already have the 13T and 15T pinions, so I guess I'll just have to try them both out. I'll just need the time - which lately seems to be a scarcer resource than $$$

The motor should be hitting about ~35k rpm with this battery, so I don't feel that's too high. As far as how much I was at WOT, the space I was was running in wasn't big enough for me to hit full speed - I was still gaining speed every time I had to brake.

It was the first real outdoor run with the 5S pack. I was getting it ready for the MMM, but the MM didn't seem to have any complaints - even pumping out a max of 1250Watts.

Maybe what lutach says is right, but just taking into considertion that it was about 50* outside and a bit damp - i'm wondering if that could translate into too hot when it 90*+ mid-summer.

[jhautz]

Those temps dont sound to bad to me. You can try going up and down like others said, but I wouldn't worry about it. It all sounds very solid to me. At least nothing to be worried about.

I feel as long as I have these temps

ESC-cool
Lipo battery-cool
Motor-warm to hot

you are doing well, when you consider how fast these motors are turning and the amount of electricity we push through them

[jhautz]

Really by gearing up, you might cool the motor down a bit, but you will increase the peak amp draw you are seeing and probably increase the MM temps. Like the previuos poster, Id rather have a cooler esc.

The more I think about it, it sounds pretty solid as is.

[VintageMA]

Cool - thanks guys, it's more than fast enough more me right now. I don't need more than 40 - 45 for a top speed - it's no fun just goin 60mph in a straight line after a while, and if I wanted that speed I would get an onroad car - which I had and got bored of real fast - bumps hills and rough stuff is where the fun is. :)

Like I said - I wasn't even able to get it to top speed as it (but I was running in the smallest lot out of my usual - there was a boating thing going on and all the big lots were packed with cars).

[VintageMA]

Was reading through another thread and think I may have found a reason temps on the motor were up a bit - running 10K in the center diff but with the torque of the 5S setup the front end was pulling up and unloading a lot. I think a lot of my acceleration was lost in front wheel spin - I might try 15K or 20K in the center and see how that does.

[jzemaxx]

Go up a tooth or 2 on the pinion. That will get the temps down on the motor.

[glassdoctor]

The rule of thumb does depend on the capability of the esc though. For example, if you have an esc that just doesn't get hot no matter what (MMM....) then you can't exactly compare temps (esc vs. motor) and figure how to adjust the gearing.

Take the fan off the MM(or put one on the motor also)... or check the temp inside the case.... and you may find that it's actually the motor that is running cooler.

158 isn't bad at all, and in this case gearing taller might = no changer or even higher temps. But there's only one way to find out. :) I'm curious to see what happens with the 13 and 15 gears

[BrianG]

Originally Posted by VintageMA

Was reading through another thread and think I may have found a reason temps on the motor were up a bit - running 10K in the center diff but with the torque of the 5S setup the front end was pulling up and unloading a lot. I think a lot of my acceleration was lost in front wheel spin - I might try 15K or 20K in the center and see how that does.

That's how I blew a 10XL on my Revo. The CD I used had too-thin oil in it and unloaded the motor too much. Overheated and after a while had really crappy speed AND really hot motor. Took the CD out and replaced the motor with a 9XL and no problems since. I just couldn't find the happy medium for diff oil that would offer better on-power cornering while not unloading the front.

[VintageMA]

Been a little while, but I tested both 15 and 13 gearing on this setup.

At 15 the motor temp was just a few degrees higher, nothing bad. Current draw did go up as well.

Interesting thing though was that at 13 gearing the motor temp shot up to almost 190* after a 10 minute run. This run was also with my new MMM.

I found it very interesting:
The buggy was very smooth on 5S compared with the MM, but my batteries were really hot - measured 140* on one spot on the battery.

I am a little concerned about that as I have never measured any of my batteries to be that hot unless I was running a way out of whack configuration to test things out.

I recall Patrick saying in one of the MMM threads that there was too much energy in the braking to dissapate the heat through the heat sink and thus the MMM was using a regnenerative power braking setup that would push the current back into the battery. This actually concerns me a lot. LiPos aren't designed to be charged at a high current - 1C is best for charging, 2 - 2.5C is possible with a balancer but will decrease battery life cycles by almost 50%. I believe NiMH can handle higher charge currents better. If this is the case, I will be very dissapointed if my battery life is decreased because of the braking method employed.

How much current do you think the braking could push back into the battery? 2C, 3C, 5C, 10C....... more?