# Electric sportbike, questions!



## antoninow (Mar 24, 2012)

Hi all!

I'm new to the forum but it seems that everyone here is very helpful so I will throw a couple of my doubts here, I am doing a project for the university where I have to design a sportbike using the TTXPG rules. I thought the first thing I need is to size the electrical motor in order to size the batteries, the controller, converter and so on... I am trying to calculate the torque required by the motor with the upper limits of everything I know I will get a bigger machine but then I will be confident that I won't have any problem moving the bike.

overall bike weight: 250 kg
driver weight: 115 kg
so that gives a total of 365 kg body to move

I have chosen since it's a sportbike to have an acceleration of 2,22 m/s^2 aprox. 80 km/h in 10 seconds, computing that I get a force of 810 N, 

If I want to find the torque I would the radius of the wheel so I am considering a 0.35 m radius, 35cm, and that gives me a torque of 283 N-m, I think this torque is outrageous!!! 

I just want to check that I am doing things properly so please if anyone can help me I would appreciate it very much. thank you!


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## frodus (Apr 12, 2008)

Welcome and good luck on the project!

I know there's lots of people that can help here, but maybe head over to elmoto.net and say hi and introduce the project. It's all electric motorcycles over there and they might be better familiar with what you'll need. (I'm over there as well)

As far as your torque, that 283N-m is at the rear wheel and unless you've got a hubmotor, you'll be using a chain/belt to the rear wheel from the motor, so you have a gear reduction. So maybe use a 4:1 ratio and now that torque becomes 70N-m, much more realistic!


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## Yabert (Feb 7, 2010)

antoninow said:


> driver weight: 115 kg!


It's a 45 Kg disadvantaged at the beginning...



> If I want to find the torque I would the radius of the wheel so I am considering a 0.35 m radius, 35cm, and that gives me a torque of 283 N-m, I think this torque is outrageous!!!


Not really! My motorcycle had more than 500 N-m at wheel (around 125 N-m at motor shaft). Please notice than this torque wasn't available (constant) from 0 to 80 Km/h!
Still, 0-80 km/h was reachable around 5 sec. But it was a 225 Kg body to move!


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## antoninow (Mar 24, 2012)

Yabert said:


> It's a 45 Kg disadvantaged at the beginning...
> 
> 
> 
> ...


Yeah the thing is that one of my drawbacks is that my driver weights 18 stones, aprox 115 kg... 

Ok, but it wasn't an in-hub motor right? so u used something to bring the rpm down but the torque up, my first thought was to use an axial flux machine in the wheel but it seems that it's a little difficult to create so much torque with a small axial machine, so that torque is not that crazy, it that's fine now I need to work out a ratio that suits the application, like frodus said something around 4:1 or maybe 3:1 should work, how big is the machine in your bike?


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## Yabert (Feb 7, 2010)

antoninow said:


> how big is the machine in your bike?


Too big! http://www.diyelectriccar.com/forums/showthread.php/suzuki-drz-sm-2005-electric-48239.html


They have few motor on those site who can produce over 100 N-m of peak torque.

http://www.electricmotorsport.com/store/ems_ev_parts_motors.php
http://evdrives.com/motors_overview_conversions.html


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