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.

[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.

[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.