under or over geared?

[steveo]

i always forget, motor and batteries of around same temp and esc alot hotter, my dog ate my temp gauge (seriously) so i cant give ya anymore info about temp, its a c-50 motor i dont know what wind it is, its not the one for the e-maxx. gearing 18/70

the 9920 seems to hold up well, even on 18 cells and it wants to take flight

[suicideneil]

hot esc + cold motor + hot battery = over geared

cold esc + hot motor + cold battery = under geared

warm everything = just right.

Thats usually 99% accurate.

[Hakan_J]

Originally Posted by suicideneil

hot esc + cold motor + hot battery = over geared

cold esc + hot motor + cold battery = under geared

warm everything = just right.

Thats usually 99% accurate.

I really wonder if "cold esc + hot motor + cold battery = under geared" is correct, it doesnt seem to be true for me atleast. I have no sticky driveline or anything like that but when I overgear my motor gets really hot but everything else stays cool

[VintageMA]

Short of plain old experience, is there any way to calculate what will be the right gearing for a certain setup?

For example - current project CRT.5 - 3S Lipo with a MM and Hacker B50 8L. Motor KV is 3019, so I figured gearing it for around 30 - 35 mph would be good without requiring too much amp draw. Based on the hardened pinions Mike had in stock for the 5mm shaft I got a 13T and a 17T. The motor got pretty hot with the 13T, so I switched to the 17T (gearing for about 45mph) thinking that would probably be way overgeared - but eveything ran nice and warm. No temp gun with me during the run, but using my finger I could tell all temps were under ~120.

[suicideneil]

"99% accurate", sometimes it doesnt hold true though, so its just a case of stocking up on spurs & pinions until you find a ratio that gives you the speed/torque you want & runs cool too. As for finding the right gear ratio, I wish there was, but even BrianG's mighty calculator can only provide the ratio needed for a certain speed on a certain voltage etc etc, it cant tell you if the motor/esc/batteries will run hot or not- just too many other variables (weight being the largest).

[lutach]

Here is my situation. I'm doing a comparison of a few ESC. My current motor is an Aveox 1412/1y. The spur gear is 51T and I ran my truck for 8 minutes with the MGM 16016-3s and the MM. The ESCs were cool and warm and the batteries (7.4V 5000mAh wired in series) were cool. The Aveox was pretty hot after the 8 minutes. I have now put a 17T pinion to see what will happen. If it gets hot, I'll try a 15T. If the 15T gets hot I'll go with a 14T. I have noticed guys in the forum running spur gears in the 40s and pinions ranging from 12T (I'm not 100% sure) to 16T pinion and they have good temps. So I'll see which one works better and drop a line here. Other people should also add their information on this as well.

[jhautz]

Originally Posted by Hakan_J

I really wonder if "cold esc + hot motor + cold battery = under geared" is correct, it doesnt seem to be true for me atleast. I have no sticky driveline or anything like that but when I overgear my motor gets really hot but everything else stays cool

Whats your setup? If you have a very capable ESC and Battery setup, but a marginal motor, it is possible to see that.

[Hakan_J]

Originally Posted by jhautz

Whats your setup? If you have a very capable ESC and Battery setup, but a marginal motor, it is possible to see that.

MM, 4s 8000mah TrueRc lipo and lehner 1940/8 geared 16/48 or 13/48 in a matrix rtr and the same setup in a matrix pro.

EDIT:
The RTR get a little hotter, I think the the RTR has higher gear ration in the diffs.

[jhautz]

Im rather surprised to see that. I would think the MM and TrueRC lipos would get stressed sooner than the Lehner 1940.

I also have a converted Matrix buggy. You are right about the diffs. They do run a screwy setup in there. The RTR and the FTE both come with 9/26 mod 1.5 gearing (2.889 ratio). Thats a really tall ratio compared to most standard diff buggys (13/43 3.308 ratio), which forces you to run what seems to be a very low pinion/spur ratio when you listen to what others are running. I found that the 13/46 was about as high as I wanted to go with the stock diffs before I started seeing heat issues.

But I am still surprised that you are seeing heat in only the motor and not the ESC.

Also, is that just a typo or are you really running a 48T spur??? Most are running 46T.

[Hakan_J]

Originally Posted by jhautz

Also, is that just a typo or are you really running a 48T spur??? Most are running 46T.

No your right its 46!

If I'm running 16/46 in my Pro I get about 170-180 F on the motor but my brother gets up to 200F in his RTR. Esc and lipos are not getting hot at all.

We will experiment with 13 pinions this weekend to see how much of a difference that makes, but still "over geared -> cool motor" doesn't fit very well for us. I really don't think that his rtr with 16/46 is under geared? Do you?

[lutach]

Originally Posted by Hakan_J

No your right its 46!

If I'm running 16/46 in my Pro I get about 170-180 F on the motor but my brother gets up to 200F in his RTR. Esc and lipos are not getting hot at all.

We will experiment with 13 pinions this weekend to see how much of a difference that makes, but still "over geared -> cool motor" doesn't fit very well for us. I really don't think that his rtr with 16/46 is under geared? Do you?

I ran a 13T/51T and the motor got pretty hot and that is a 3.9:1 ratio. Now with the 17T/51 it will be a 3:1 ratio. This to me will make everything run hotter right? Let me know how the 13T/46T (3.5:1 ratio) turns out.