Motor "Sweet Spot"
 

I was looking over some rpm charts for various BL motors and noticed they can have quite a high amount of winds, which brings the kv down to as low as ~500. On these motors, is the sweet spot still 35k-38k rpm? If so, then they must be designed primarily for high voltage. For example, motor with a kv of 500 would need 76v to reach 38k rpm. I'd imagine the current would be quite low though.

Yes, in a car, the "sweet spot" is usually around 35 to 40k even for those motors. Just remember, most of these are intended for planes. From what I understand, the motor on a plane doesn't spin as fast. I think around 25k. Not really sure why.

Planes need to run limited RPMs because of the propellors that they use. But, they can use gearboxes on the motors, so there's no reason why a plane can't have a motor spinning faster.

Are these motors with a kv of 500 outrunners or (standard) inrunners? Outrunners function differently, and work with a much lower RPM.

Well, the reason I ask is I was thinking of doing a direct motor-to-diff drive using a lower rpm motor, but if they are still supposed to spin at such high rpms, then it wouldn't be a good idea. I was also thinking of using one of those inline planetary gear drives, but they are quite expensive. I was shooting for a semi-realistic car where the motor is in the front, followed by the "tranny". But, it looks like I'll still be using a spur/pinion arrangement.

The ones I was looking at were from the Feigao charts, so I assume they are inrunner types.

Sweet Spot, i've seen a lot of that in threads, but if my calculations are correct. I'm running around 28,000 right now with 16 cells. Is that a bad thing? If I were to run 20 cells, that would bring me over 30,000+...

Thats why I'm going with 6S LiPo. That should bring the motor to life....

I'm worried if i go 6s LIPO, my controller will be getting close to limitations...so i think i'm going 5s, what controller are you running squee?

9920. Chances are I will get my packs in the next couple of weeks so I'll let you know how hot it gets. I wouldn't however worry. With a 10XL, it won't be pull a bunch of amps. Plus, people were running 20+ cells on a 9920 way back when they were only rated for 18 cells.

Sounds good. You just got me a little worried cuz you advised 5s earlier. But now thinking 6s! LOL, never too much power if a system can handle the juice! I'm runnin the same that you are i think. 9920/10xl wanderer?

Yea, except I have a Feigao. Same thing though.

Ok, PM me when you have a few test runs if you could please. In the end of all though (it'll be a few months), I would like the Quark 125B with a lehner 1950/8 on some lipos. For now, I'm going to look more into lipo, chargers, balancers, and an LVC. When I get some solid info and made decisions, I'll get the lipo first, then a new system...thinking maybe doing a Revo for the next project...

The sweet spot is where the motor operates most efficiently. You can probably get a little more than 28k rpm on 16 cells. For one thing, that is assuming a nominal 1.2v per cell, but cells can be as high as 1.3+ on a full charge. Also, the actual kv rating you are using is its "loaded" value, which is dependent on weight, gearing , etc. The 10xl's unloaded value is 1668rpm/v. Those kv values are probably average values too, so there is some variation. Depending on weight and other factors, you can probably get between 30k-32k rpm on 16 cells.

I see. I did do the calcs at 1.2. But i noticed my cells with no load are at 1.45, 1.43 or so. My gmaxx is i think close to 12lbs. Gearing right now is 20/51 mod 1, I know there is a calculator for all this, but can't find it! Anyone know what rpm's i would be close to? with the above info?

Funny you should mention that, since I have one: Speed Calculator :)