9000kv motor on 2S vs 4500kv motor on 4S?

[Mr_Procrastination]

Good day,


As per title,

9000kv motor on 2S vs 4500kv motor on 4S?

Why would / could one choose one over the other?
Im I correct in understanding that the rpm output would be the same?
Difference in torque maybe?
One is cheaper than the other?
If one had a esc that supported both 2-4 cell then 4 cell could be used with higher voltage to reduce amp draw at any given wattage?

Thanks for your thoughts

Timon

[XLR8]

Setting aside the motor performance question and focusing on economics, I guess I'd be more inclined to invest in a faster motor than a higher voltage battery. A 4s lipo will probably be larger, heavier and more expensive than 2s with a similar amperage rating. All lipo's have a finite life and will need to be replaced at some point in time. Brushless motors on the other hand, if they're not overheated, will last a lifetime. Just my 2 cents.

[Mr_Procrastination]

Thanks for your reply.
Yes I suppose the cost of same watt/hour 4 cell (say 2000mah) to a 2 cell (say 4000mah) would / could be higher.
Same would go for the motor less turns = less manufacturing materials? But saying this Im sure the motors at least are just sold at a price point irrespective of actual manufacturing cost whether its a 5, 10, 15 turn of the same type / brand.

Cost aside though?
Why pick one over the other?

[ChaosKevin]

Interesting question. I would guess that higher voltage would be more efficient but I wonder if the added efficiency isn't offset by the added weight of the battery. Higher voltage and lower current should equal less energy lost heat because of resistance.

This is almost totally a guess but feel like ESCs may lose effeciency at higher frequences, could be another factor.

This is theory based on some old, dusty electrical knowlege. I would give much more weight to some real-world experience over anyting I have proposed.

[Mr_Procrastination]

Aren't high turn motors renouned (spelling... Im stuffed when spell check can't solve it), for their torque qualities. E.g. high turns in crawlers? What happens if one goes and puts a low turn motor on 1s in a crawler? Heat? Amps through the roof? Maybe a super expensive esc that can handle 120amp on 1S, if they exist?
Slugging the motor out at low rpm when it should be rev happy...

[jwscab]

Essentially you are talking about the same power or wattage, but the higher voltage will yield better efficiency.

Based on your example, these combinations would be pretty ridiculous either way. A 4500kv motor on 2s would be a pretty hot 10th scale setup. On 4s that would be basically uncontrollable.

As the kv goes up, torque goes down.

[Dadio]

My understanding was that efficiency is better with higher voltage battery and lower KV motor given an otherwise equal theoretical performance , I'm sure that's how it was explained to me , something like higher voltage = lower amperage and lower losses in the wiring etc making for a cooler running setup , more of the suger turning to alcohol etc .