Combining Motor and Pedal Power – Best Practice

[Introquest]

I’m currently designing a mid mount motor drive bike and have a question concerning proper/best practice motor reduction and optimum pedal input. I’m considering using a 2-3KW motor connected to a pedal crank via a cyclone or similar arrangement so I can pedal along. If I want to pedal throughout the entire speed range of the motor would it make sense to gear the motor down to 60-70 max rpm? By running the pedal/motor output through a 7 speed cassette on the back wheel should I then have good low speed torque at one end and high speed at the other while being able to peddle all the time? Has anyone set their ebike up like this or have actual experience with best practice of combining motor/pedal input?

[Thud]

https://www.google.com/webhp?sourceid=n ... 91&bih=811

https://www.google.com/webhp?sourceid=n ... 91&bih=811

the answer is allways "Yes"
But sometimes with a cavet.

That should get you some ideas.

[Introquest]

Thanks for your reply. I read through the links but no direct reference to my answer. What are the caveats?

[flyinmonkie]

In my experience, if you run the motor through the cranks, then it is very hard to gear the pedals and the motor to work together. To do it, you have to gear the motor down to pedal cadence. Otherwise the pedals and the motor are going in different directions in terms of gear ratios.

If you have a hardtail, then you can run 2 chains to the rear wheel and you can gear the motor and the pedals separately. That way you can gear them individually to match each other.

Hope that made sense.

Clay

[biohazardman]

Yes, it's nice to be able to get your RPMs down to where you can keep up withy the pedals. That does mean plenty of reduction though. Here is one person that has done it well and with style too. viewtopic.php?f=28&t=25193

[Warren]

Introquest,

Pedaling 60-70 rpm is too slow to be able to put out much power, for an extended time. You need to put out 75-150 watts continuous to make a meaningful contribution. Doing it at 60 rpm will mean using slow twitch, muscle fiber. This is fine for anaerobic stop light, or hill sprints. But to put out useful power for more than a few minutes requires aerobic muscle use, and a higher, lighter cadence, 80-90 rpm. Trained bike racers spin 90-120 rpm for days.

Frankly, on a bike with 2-3 kW of power, even a bike racer's 250 watt, long term cruise input, will only add 10 percent! However, making your legs go around may feel good, and deceive the authorities.

Warren