# University design project-motor selection for e-bike pedal assist



## rosselboss (Feb 9, 2016)

As the subject states I’m having a little bit of trouble choosing a Brushless Dc outrunner motor for a university engineering design project and was wondering if I could get some general advice/suggestions. 
A little background on the project, we are building a universal electric bike attachment, the purpose being able to install/uninstall the whole attachment in a few minutes. 
The brushless motors (2 of them ) will be used as friction rollers to propel the rider forward by pinching the back tire. This will act as an assist to pedaling and NOT the sole power delivery system. 

Our biggest hurdle right now is cost (budget of $600 materials and assembly/machining included). Initially we were going the route of using (x4) 5s batteries hooked up -2 batteries each in series- then each of those pairs hooked in parallel to give us the desired voltage and current necessary for our estimated ride time of 1/2 hour at approx 15-18mph. 
(x4) 5s vs (x2) 10s were chosen based on battery and balance charger cost 
Again these specs can change once a motor is selected.

However finding a motor to handle this high current has been tough, motors at these specs seem to cost approx $100 apiece.

So to get to the point of this thread should I keep looking in this 5s battery/motor range or decrease both size of the motors and batteries to possibly 3/4s? I do realize this would save a ton of money on the project however the range and max speed will be significantly decreased.
If you have any more detailed questions do not hesitate to ask 

Thanks in advance for your input,
Ross Peterson


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## ta_man (Apr 10, 2005)

*Go To Rc-Monster*

Go to RC-Monster.com forums. In the "General Electric" sub-forum there is a guy who has built at least one and maybe more than one E-Bike. I am sure he knows more about them than anyone here likely to read your post.

Your budget may be a show-stopper, but he is still likely to provide you with some good info.


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## rosselboss (Feb 9, 2016)

@ta_man 

Appreciate you pointing me in the right direction!


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