# Upgrading my 8kW friction drive?



## TAz00 (Aug 2, 2010)

Hi there, new user here 

I have recently built an electric mountain bike, with information from several sites, this included.

I bought a brushless RC motor, rated for 130A, and I am running that with a pair of 8S 5800mAH + 4S 5800mAh batteries, giving me a total of 11,6 Ah @ 44 Volt.

The motor is powered by a 120A (180A 10sec burst) motor controller (as the 200A Monster controller arrived broken)

So this thing almost delivers 8kW, needless to say, as the pictures also will tell you, is that it is absolutely shredding my tyres, and anything I try to increase grip with. Otherwise its so much fun to ride, and people cannot help turning their heads to look 

This is where I am stuck. 

Either i go for chain drive, for which I will need a new freewheeling crank and a small sprocket for the motor. As far as I can tell, the crank is pretty expensive? 
What is the best chain drive you have seen? And which online stores do you recommend?

Second idea is to find a way to fix the slip in friction drive.

*Pictures are a wee bit huge
http://taz00.com/eBike/S5000881.JPG...00883.JPG http://taz00.com/eBike/S5000884.JPGhttp://taz00.com/eBike/S5000881.JPG
http://taz00.com/eBike/S5000882.JPG
http://taz00.com/eBike/S5000883.JPG
http://taz00.com/eBike/S5000884.JPG


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## major (Apr 4, 2008)

TAz00 said:


> I bought a brushless RC motor, rated for 130A, and I am running that with a pair of 8S 5800mAH + 4S 5800mAh batteries, giving me a total of 11,6 Ah @ 44 Volt.


Hey TAz,

I think your problem is speed ratio between the motor (drive drum) and wheel. Those RC motors are screamers, aren't they? Like over 10,000 RPM? If you have a 2.6 inch drum on a 26 inch wheel, that is a 10:1 ratio. That's like 80 mph. 

Friction drives like this will always be a problem. I saw tire wear even with a wimpy low speed brushed motor with like a 1 inch roller. And watch out for motor heat without the air blast from a prop cooling it.

Good luck,

major


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## TAz00 (Aug 2, 2010)

The speed is ok. Its a 130kV motor, Turniqy one. I calculated the speed from the diameter of my machined roller which fits over the motor to match 65 km/h and it does 68 km/h downhill, so the problem is with the torque this thing puts out. (not with the 44v but 33v 8S setup)


Another idea was to machine my own hub motor case to put the motor inside. 

Or a belt drive maybe?


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## roflwaffle (Sep 9, 2008)

TAz00 said:


> Either i go for chain drive, for which I will need a new freewheeling crank and a small sprocket for the motor. As far as I can tell, the crank is pretty expensive?


Why do you need a freewheeling crank for the motor?


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## TAz00 (Aug 2, 2010)

This video explains it 





I still want to be able to pedal, without my feet getting dragged around by the motor


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## roflwaffle (Sep 9, 2008)

It seems like you just want a flip-flop hub w/ the motor on the locked side and the freewheel on your side. It shouldn't be more than $40 shipped, provided you have the cogs already.


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