Can I run two Magic Pie 5 motors at the same time? 20" and 26"

[Phil Booth]

I have a 20" Magic Pie 5 on the front wheel of my wheelchair hand-cycle trike which works great for outings on road. With this setup I use standard wheelchair wheels on the back.

I also have a rear end clip on setup to the same hand cycle trike for more off road use which runs 26" fat bike wheels. I would like to buy a Magic Pie 5 for one of the fat bike wheels so I can get up steep gravel hills as the front wheel drive just starts skidding.

I use the bike on pedal assist.

So my questions are.
Can I run two Magic Pie 5 motors at the same time or do I need to switch between them?
Can anyone foresee any issues running 20" with 26"?
What extra equipment do I need to buy?

I appreciate your help thanks Phil

[Bikemad]

Hi Phil andto the forum.

You can certainly use two Magic Pies at the same time, but I'm not 100% sure whether a single pedelec sensor will be able to work with two controllers as I have not tried it. 
A single throttle is usually fine with a dual Pie setup, so the pedelec sensor may be OK too.

You would probably need to reduce the maximum current on both motors to 15 Amps (or less) to prevent a single battery from being overloaded.

Because of the difference in wheel sizes, you would also need to reduce the maximum rpm of the 26" wheel to ensure it is not constantly working harder than the smaller 20" front wheel:

It is definitely possible to combine both motors in one bike, and running dual motors should actually increase the efficiency of the available battery power as each motor is likely to be working under less load which usually results in a more efficient power output.

However, if you have different sized wheels front and back:



You could find that the smaller front wheel may not be contributing very much assistance at lower throttle settings, but reducing the maximum rpm of the larger rear wheel to produce the same road speed as the smaller wheel at maximum rpm should help to balance out the motor load more evenly.
For example, if the maximum unloaded rpm of the front motor was 400rpm and you were using a 26" on the rear and a 20" on the front, you would have to set the maximum rpm of the rear wheel to ~308rpm (400/26*20) to produce the correct throttle to rpm ratio to provide an equal road speed on both wheels.

The maximum effective unloaded speed would then be limited to that of the smaller wheel (23.8mph or 38.3km/h) but it would be a lot more efficient than the rear wheel doing all the work at lower throttle settings.

I'm not sure how much the steering would be affected under load (and regenerative braking forces) on the offset driven rear wheel, I imagine it would probably be very similar to driving a motorcycle with a side car.
If it was too annoying to live with, you could simply add another MP5 to the other side to balance the power and braking forces and eliminate the torque steer.   

Alan
 

[Phil Booth]

Thanks, Alan
It sounds like I could run 2 or 3 completely separate setups each with their own battery. I was planning to run separate batteries anyway.
So by setting the rpm I could get similar work out of each wheel and 38.3 km/h is certainly fast enough for me.
Do you think it would be best to run three Magic Pie 5 wheels?
I thought this might be a little bit of an overkill but I guess it would look the best with matching wheels.
My guess is that it would probably perform better under heavy braking and exhilaration with all three wheels being driving wheels

I guess my main question is still whether the one pedelec could run two or three wheels.

Cheers
Phil

[Bikemad]

Three Magic Pies at full power would probably be too much power, as it would simply spin the front wheel every time you accelerated (and there would be no need to pedal anymore if a throttle was fitted).

Two rear Pies with two batteries would be adequate on their own, but having the extra weight of the front mounted Pie would help to keep the front wheel on the ground.
If the front motor was connected to the rear motor's batteries, it could be set at very low current (enough to overcome the residual drag without actually producing much tractive power) and it could also be set to provide more regenerative braking force than the rear motors if required.

Putting a second drive wheel (and its own battery) on the rear will add a lot more weight (and expense) and you may find that it is not really necessary.

I would be tempted to try adding a single motor on the rear first and see how it goes.

Unfortunately, without actually connecting the pedelec sensor to dual (or triple) controllers, it is difficult to know for sure if it will work.
If you have room to fit a sensor on each side of the pedal crank, this should (hopefully) allow two motors to be controlled by separate sensors if they can't be controlled by a single pedelec sensor.

Alan
 

[Phil Booth]

Awesome,
Thanks, Alan.
I will let you know how I got on.