Comment, criticize my build. But be nice I’m new!

[Hummina Shadeeba]

If u don’t have pedals you can’t go over the Golden Gate Bridge! Also it now becomes obviously illegal. I’d get a wider bottom bracket to get the cranks and pedals wider. Even better would be to get freewheeling cranks and do a jackshaft

 

[Drubieg]

Here's your current ratio (based on estimated loaded RPM):

View attachment 369804

And a 'ballpark' estimate what it likely should be for single stage reduction:

View attachment 369805

Ratio 14 to 1. (which requires a driven sprocket of 126 teeth.

Haha 126 that’s bonkers

 

[Papa]

Haha 126 that’s bonkers

You wanna know what "bonkers" really is? With a dinky 9t spinning at six grand, you'll likely be doing roadside chain re-installs on regular basis. That is... unless the chain decides to exit to the inside, and snag the rear wheel... potentially locking it.

 

[Hummina Shadeeba]

Haha 126 that’s bonkers

Freewheeling crankset with wider bottom bracket so can fit pedals and a jackshaft would be the normal way

a 126t using a #25 chain sounds reasonable and it’s got a 1/4” pitch vs a common 8-speed chain with 1/2” pitch. So half the diameter. I use 70t with 8-speed chains and that’s commonly done. Better yet do a 140 or 150t and also increase the motor sprocket teeth count a couple .. but that’s a guess and I’d do the freewheeling cranks n jackshaft.

 

[Papa]

.... a 126t using a #25 chain sounds reasonable...

Auh... nope. #25 won't last, he'll need #25H at a minimum. And that's even marginal considering 3kW pulling on it.

 

[Hummina Shadeeba]

Auh... nope. #25 won't last, he'll need #25H at a minimum. And that's even marginal considering 3kW pulling on it.

I’ve never tried #25h size but seems commonly used for powered vehicles

It generally shows 1/3 the strength of an 8-speed chain (#40).

Or could use #35.

 

[PaPaSteve]

Tunderstruck Motors in Santa Rosa could be a resource.
Good guys.

Gear Ratio Calculator

Calculate your gear ratio for your electric vehicle conversion project using ThunderStruck Motors' Gear Ratio Calculator

www.thunderstruck-ev.com

Did your BMX bike have one piece cranks ?
Is the rear sprocket bolted directly to the hub, no freewheel ratchet ?

Axle Sprockets and Hubs for #35 Chain - ElectricScooterParts.com

#35 chain axle sprockets and axle hubs. For electric go-karts, beach wagons and beach carts.

electricscooterparts.com

 

[BiggKidd]

Have you considered belt drive?

That's one of those Vevor motors isn't it?

I've just stared acquiring parts for a full frame and all custom E-bike build, mine will have pedals and a slightly smaller motor in physical size .

 

[Drubieg]

Tunderstruck Motors in Santa Rosa could be a resource.
Good guys.

Gear Ratio Calculator

Calculate your gear ratio for your electric vehicle conversion project using ThunderStruck Motors' Gear Ratio Calculator

www.thunderstruck-ev.com

Did your BMX bike have one piece cranks ?
Is the rear sprocket bolted directly to the hub, no freewheel ratchet ?

Axle Sprockets and Hubs for #35 Chain - ElectricScooterParts.com

#35 chain axle sprockets and axle hubs. For electric go-karts, beach wagons and beach carts.

electricscooterparts.com

I think it’s a 3 piece but have to check. And yes it’s bolted directly

 

[Drubieg]

Have you considered belt drive?

That's one of those Vevor motors isn't it?

I've just stared acquiring parts for a full frame and all custom E-bike build, mine will have pedals and a slightly smaller motor in physical size .

I thought about it but looked like belt drive stuff wasn’t as available. It’s technically a kunray, I got it from electro & company

 

[PaPaSteve]

I’ve never tried #25h size but seems commonly used for powered vehicles

It generally shows 1/3 the strength of an 8-speed chain (#40).

Or could use #35.

Bicycle chain has an extraordinary high strength to weight ratio compared to industrial chain.
Also consider bike chains are designed to operate at much lower RPM.

 

[PaPaSteve]

I think it’s a 3 piece but have to check. And yes it’s bolted directly

3 piece allows options for very wide spindles that may help the cranks clear the motor.
Sprocket bolted to the hub could help slow the bike depending on the controller.

 

[PaPaSteve]

Thunderstruck Calculator
Beware, sprocket terminology is confusing.
"Sprocket teeth' should be "motor teeth"
Chainring teeth" should be "drive wheel teeth"
enjoy

 

[Drubieg]

3 piece allows options for very wide spindles that may help the cranks clear the motor.
Sprocket bolted to the hub could help slow the bike depending on the controller.

Alright cool. And yes it does seem to help

 

[Drubieg]

Thank you to everyone who had input for me! I have a good amount of info here to work from… I appreciate all of your help and I’ll update once I’ve accomplished addressing my set of issues with my build.

Andrew

 

[bengxe]

Another option you have is just rewiring your batteries to parallel the 4 36v packs to halve the motor speed. You should still be able to hit 2500ish watts with your 66amp controller. You could go to a bigger motor sprocket and then maybe still have to go smaller on the rear.

 

[Drubieg]

Another option you have is just rewiring your batteries to parallel the 4 36v packs to halve the motor speed. You should still be able to hit 2500ish watts with your 66amp controller. You could go to a bigger motor sprocket and then maybe still have to go smaller on the rear.

This is interesting, this would be ok to run a 72v motor on 36v? It wouldn’t damage the motor?

 

[BionicOnion]

This is interesting, this would be ok to run a 72v motor on 36v? It wouldn’t damage the motor?

You would need a controller that's suitable at the lower voltage but yes, the motor won't know the difference

 

[Drubieg]

Tunderstruck Motors in Santa Rosa could be a resource.
Good guys.

Gear Ratio Calculator

Calculate your gear ratio for your electric vehicle conversion project using ThunderStruck Motors' Gear Ratio Calculator

www.thunderstruck-ev.com

Did your BMX bike have one piece cranks ?
Is the rear sprocket bolted directly to the hub, no freewheel ratchet ?

Axle Sprockets and Hubs for #35 Chain - ElectricScooterParts.com

#35 chain axle sprockets and axle hubs. For electric go-karts, beach wagons and beach carts.

electricscooterparts.com

I see a 114t sprocket here, seems close enough!

 

[bengxe]

You would need a controller that's suitable at the lower voltage but yes, the motor won't know the difference

The only reason this might be true is if the controller has a non-programmable low voltage cutoff.

 

[Hummina Shadeeba]

That controller is huge for only doing 66amps. For 80$ could get a vesc 75100 or similar and do 100 and use the motor as a regen rear brake to simplify with two-way throttle, also can hook up Bluetooth to see lots of stuff, run a foc program so smoother and quieter, and it can do either voltage. I’d do 72 and do the biggest chainring u can find with a #35 chain

 

[BiggKidd]

I thought about it but looked like belt drive stuff wasn’t as available. It’s technically a kunray, I got it from electro & company

Often times you have to look outside of the "project" type parts and use pieces from other industries to create what you need!

I ordered an even higher RPM motor than what you have. I think I'll be using the rear pulley off a 454LTD and unless I come up with something better I'll have the drive pully made.

 

[Hummina Shadeeba]

With using these high speed motors that you’re running slowly it works but you’re turning a Ferrari into a Toyota. At least you need to get a controller that can put out a lot of amps or it’s a double-weak Toyota.

 

[Drubieg]

I've seen adapters to put u-brakes like you have in the rear in place of the side pull you'd have to use on that fork. That seems like it'd be an improvement.
#35 sprockets exist up to at least 85t, if you can tolerate the noise and chain wear from the 9t you might be able to make your single stage work. I think I would
I'd think you also need to find a way to stop over drawing your batteries. If that controller isn't programmable you could use a cycle analyst to limit the current, or maybe add another parallel group on the front of the handle bars.

I bought 2 more 36v batteries to put in parallel for the current draw. Still looking into either a 2 stage gearing deal or if I wanna go with the 114t rear sprocket with a free spinning sprocket to add chain wrap to the 9t

 

[BiggKidd]

With using these high speed motors that you’re running slowly it works but you’re turning a Ferrari into a Toyota. At least you need to get a controller that can put out a lot of amps or it’s a double-weak Toyota.

Long as the gearing is correct or at the minimum in the correct range then these high RPM motors with matching controllers should run like a scalded dog!