ASK Cub Reporter, 04.11.2012, Version- Your Questions, My Snotty Replies

Dear Cubby,
Here is a battery question for you. I know a higher C rated battery would make a brushless truck go faster, but what would one do on my ready to run Stampede? Awesome job on the site by the way.
Seth E.

Cubby– Hey now, what’s up Seth? Good question, so here it is on the front page of BigSquid.

Will a higher “C” rated Lipo make a Joe Blow brushed motored truck faster than one powered by a lower “C” pack? The answer is… wait for it… Maybe.

Let’s say you have two Lipos from a fictitious battery company called “Happy Flower”. One pack is 20C and the other pack is their 40C model. Then yes, most likely the higher “C” pack will make make any car/truck faster than when using the lower “C” pack. Typically the higher “C” pack will maintain a higher voltage on any given load than their lower “C” pack. So… on a greater load like a hot brushless system it will be faster, and on the lesser load of a RTR brushed motor it will also be faster.

However… lets say we now have two Lipo packs from different manufactures. Lets say one pack is the “Happy Flower” 40C, and the other pack is “Billy Bob’s Batteries” 20C. Without testing there are no guarantees the 40C will make your truck faster than the 20C. We’ve proven it time and time again in our Lipo shootouts that one brands lesser “C” pack can indeed be faster than another brands higher “C” pack. There are two common ways to find out which pack is the fastest- drive them in your truck and see which feels faster, or use a high current discharger like the West Mountain CBA to see which puts out the highest voltage under load.

I am looking at two different motors, one is 4600kv and the other one is 5700kv, which one is faster?
Chester

Cubby– Ya know Chester I just love “which is faster” questions, seriously, for some reason they just make me smile.

So… in theory the 5700 kv motor should be faster right? I mean it puts out 5700 rpm per volt of input verses only 4600 of the other motor. But going faster means more power, and the measurement of raw power is wattage. There are small 20 mm 9000 kv motors that are only good for 100 watts, while there are 36 mm 4600 kv motors capable of well over 500. I can assure you the larger 4600 kv 500 watt motor will power most any car to a much higher top speed than one equipped with the tiny 9000 kv 100 watt motor.

But lets assume both of the motors you are looking at are the same size and from the same manufacture. Lets say you use the same cell count and gearing on both, then yes, the 5700 will feel faster. But… lets say you run the 4600 on a 3S Lipo and the 5700 on only 2S, then the 4600 would feel much faster. Or lets say you run 2S on both, but gear the 5700 with only a tiny 13 tooth pinion, but run a 26 tooth on the 4600, then the 4600 would again feel faster.

To boil it down, how fast you go depends on how much wattage your motor is putting out, and kv isn’t a measurement of power, only of rpm per volt of input. You don’t see Nic Case using ridiculously high kv motors, you see him running extremely powerful, high wattage motors.

Lastly, its quite likely that both motors you are looking at will put out wayyy more power than your truck can handle, it’s just that the lower kv unit will require either taller gearing or a higher cell count to feel as fast as the higher kv unit.

Yes indeed you have suffered through yet another agonizing “ASK Cubby”, submit your questions, non-sense, and merciless ridicule to Cubby at BigSquidRC dot com!

YOUR Cub Reporter