Who could rewind my outrunner?

[Metallover]

I am working on my e-bike project. I picked up a 100a suppo esc from hobbycity along with a 250kv outrunner. It is wayyyy overgeared. Could somebody rewind it to a lower kv? About how much would this cost?

I don't know what kv I need either. I'll need to calculate the gearing. What does it take to figure out how chains and sprockets effect gearing? Is it just like a spur/pinion?

and since pics always help -




edit - tell me if the pics don't work. Might have messed them up.

[sabongi]

try using a faaar smaller pinion...

[Metallover]

I can't get too much smaller...

[johnrobholmes]

What is your total geardown on that sucker?
What is your voltage
What speed do you want to hit?

geardown is just like an RC. Find the ratio between pinion/ spur, and then multiply by the ratio on the second and third reduction.

[johnrobholmes]

I see now you are using a stoker setup. Can you run the chain from your stoke hub to the biggest ring on your cranks?

[sabongi]

Have you tried using a big spur on the upper right side of the bike?

[Metallover]

Originally Posted by johnrobholmes

I see now you are using a stoker setup. Can you run the chain from your stoke hub to the biggest ring on your cranks?

I could do that but I'd have to get a couple chain links and the pedals would spin really fast. I might do that if rewinding it proves impractical for the cost.

sabongi - That part is a freewheel and acts as a pinion. Making it bigger would make the gearing even worse.


The gear reductions are - 11/72 to the "spool", 14/32 to the crank, and 48/12 to the wheel in top gear. I want to get about 35 in top gear. The motor is 250kv at the moment and I'm running 24v. That's 6000rpm. The wheel has a 13" radius so 2pi13=81.7 inches/revolution.

I'm not quite sure on my math, but I think I get 1,584 rpm at the wheel so that's... holy sh!t - 180mph!! - Someone check my math...

I figure I will need 1,168rpm at the motor so thats... 49kv.


Is this going to work out or will I need to make some major changes to the gearing?

[whitrzac]

Originally Posted by Metallover

I could do that but I'd have to get a couple chain links and the pedals would spin really fast. I might do that if rewinding it proves impractical for the cost.

sabongi - That part is a freewheel and acts as a pinion. Making it bigger would make the gearing even worse.


The gear reductions are - 11/72 to the "spool", 14/32 to the crank, and 48/12 to the wheel in top gear. I want to get about 35 in top gear. The motor is 250kv at the moment and I'm running 24v. That's 6000rpm. The wheel has a 13" radius so 2pi13=81.7 inches/revolution.

I'm not quite sure on my math, but I think I get 1,584 rpm at the wheel so that's... holy sh!t - 180mph!! - Someone check my math...

I figure I will need 1,168rpm at the motor so thats... 49kv.


Is this going to work out or will I need to make some major changes to the gearing?

I think your best bet would be to get a 3s lipo
IDK if a flux capacitor will fit on a bike though

[Metallover]

I think another 5/1 gear reduction will do the trick. Ill see if I can figure out a way to do that tomorrow.

[crazyjr]

Originally Posted by Metallover

I could do that but I'd have to get a couple chain links and the pedals would spin really fast. I might do that if rewinding it proves impractical for the cost.

sabongi - That part is a freewheel and acts as a pinion. Making it bigger would make the gearing even worse.


The gear reductions are - 11/72 to the "spool", 14/32 to the crank, and 48/12 to the wheel in top gear. I want to get about 35 in top gear. The motor is 250kv at the moment and I'm running 24v. That's 6000rpm. The wheel has a 13" radius so 2pi13=81.7 inches/revolution.

I'm not quite sure on my math, but I think I get 1,584 rpm at the wheel so that's... holy sh!t - 180mph!! - Someone check my math...

I figure I will need 1,168rpm at the motor so thats... 49kv.


Is this going to work out or will I need to make some major changes to the gearing?

it's been a while since i was in school, but i thought it was pi X diameter, not 2pi X diameter. if you do single diameter you get 40.82. Still moot point because if everything else is right, you are still looking at 90 mph and still need further reduction or lower kv

Originally Posted by crazyjr

it's been a while since i was in school, but i thought it was pi X diameter, not 2pi X diameter. if you do single diameter you get 40.82. Still moot point because if everything else is right, you are still looking at 90 mph and still need further reduction or lower kv

metallover's right... It's 2*pi*r to get circumference or a circle

[Snipin_Willy]

nice project, but you think you could have chosen something other than a lead weight to put a motor on? Those Mongoose bikes are HEAVY!
Maybe make it a downhill battery charging bike?

[crazyjr]

Originally Posted by Bad Karma

metallover's right... It's 2*pi*r to get circumference or a circle

My bad, didn't see the radius, I assumed diameter

[Metallover]

Originally Posted by Snipin_Willy

nice project, but you think you could have chosen something other than a lead weight to put a motor on? Those Mongoose bikes are HEAVY!
Maybe make it a downhill battery charging bike?

It is a heavy bike... Its really heavy with the new stuff too! I think it was 35 before the stuff and now it's probably 65+ pounds.

To all those who checked my math, it seems I did it right? I sure hope I did. I'll figure out a good way to do the rest of the reduction at school today. Nothin better to do....

[johnrobholmes]

Another 5:1 would be your best bet. Can you pedal at 35mph though? search google for top hat adapter, you could put a 36t sprocket on your disc brake side and get all the geardown you need with your stoker setup.
Just going down in KV won't help, you will loose all of your power.