gear ratio;s

[jimbob]

im thinking of using an outrunner brushless motor
it will have 12 poles :018:
im wondering what gear ratio's everyone thinks i will be able to get away with
it will only do upto 20,000 rpm
just wondering it i can get away with a gear ratio of around 7~9:1
or will this be easy for a outrunner with 12 poles
i see with the inrunners probably with 2-4 poles they run around 15:1

it will be running 6" tyres

[BrianG]

What ESC are you planning to run? I heard the MM can run multi-pole motors, but 12 might be too much. The Quark 125, for instance, has special settings for outrunners.

As far as gearing: Outrunners are known for having higher torque ratings. So, you can gear higher than you would an inrunner. If you have the spurs/pinions, I would start at a typical inrunner gearing (maybe higher to account for the reduced overall rpm) and then go up from there.

[jimbob]

i got the esc sorted no probs there
it can run 12 pole easily and have 80A constant and 100A bursts

ya problem is im trying to design it all before buying
it will have 4.3 diffs
then just a centre diff with 50t spur

i guess i may just have to buy pinions 15-25 and try it that way :eek:
it should essentially have 3 times the torque at a set voltage F=BIL and all that

[BrianG]

Well, if you assume 20k as the max rpm, you can use my Speed Calculator to try different arrangements to get the speed you want. Then, get a few pinions around the calculated value to play around.

[jimbob]

i got 44mph with a 24t pinion
so that seems about right

20t = 37 mph
24t = 44 mph
28t = 52mph

that seems pretty good i reckon

[BrianG]

Yep. I'd start with the 20T just for safety's sake and go up from there...