Dual drive, MP4 back and SP4 front, settings?

[Haggan]

Hej.

My wife's bikes front fork was destroyed by the Smart Pie 4 so now I am playing with it. Trying dual drive.
Got it working but not good. Front wheel is doing most of the work rendering bad battery performance. Any tips on what settings should work to get this even out.? I lowered the acceleration but left everything else standard 48v settings.

[Bikemad]

If you are producing more power, the range will obviously be reduced, but if the battery is unable to cope with the additional load, you will need to reduce the power being drawn by each of the motors.

Start by reducing the Battery drawn current setting to 10 Amps on the front motor and 20 Amps on the rear, giving a combined maximum of 30 Amps load on the battery.

If you are using a single throttle to control both motors, you may also want to try reducing the Maximum Forward speed (rpm) on the front motor until the two motors spin at approximately the same speed at different throttle positions. You will need to hold both wheels off the ground at the same time (or place the bike upside down on a piece of carpet etc.) to synchronise the wheel speed under no load conditions.

Which part of the front forks failed on your wife's bike?

Perhaps you can post some pictures of the failure.

Alan
 

[Haggan]

Hej Thanks for the answer!

Yes, I definitely need to change something. Now the SP4 is doing all the heavy lifting. Also, it must be something wrong with the hall sensor since the speed is not the same if I plug the display to the SP4. I will test later with dual displays.
Maybe need to get an RPM counter or something. Or maybe I can use a magnetic bicycle sensor.

[GM Canada]

Ouch, Please use torque arms

Gary

[Bikemad]

An oversized outer diameter  "C" washer can also cause the forks to fail due to the clamping force being applied to the wrong part of the dropout:

This is my fork, do I need to change it ?
http://www.srsuntour-cycling.com/dstore/products/Forks/2640/M/SF10-M3000-AL+26'.html?sid=1

I would think those suspension forks should be OK to use provided a pair of suitable torque arms are fitted, but you might need to modify two of the supplied axle washers to fit properly inside the "C" shaped recesses on the outside of the fork dropouts to provide a nice flat surface for the torque arms to press against when the axle nut is tightened:



The outside diameter of the washers should be small enough to just fit inside the recess and should ideally be chamfered/radiused on the outer edge of the inner surface so that it does not apply any outward force at the outer edge of the washer.
If the washer is too large (or not chamfered or radiused to allow clearance for the fillet inside the recess) just tightening the axle nuts could exert enough pressure to force the dropouts apart causing the casting to crack:

If the outer diameter of the "C" washer (or even the standard tabbed torque washer) is too large, it would have to be filed (or ground) down until it fits comfortably inside the dropout and only touches against the flat surface inside the fillets.
After carefully studying Haggan's photo, it is clear to me that the failure of these forks was probably due to the axle washer (or possibly the nut itself) being clamping against the radius of the fillet around the dropout instead of the inner flat section of the dropout.

The tightening of the axle nuts would have placed a tremendous spreading force upon the cast dropouts, resulting in the failure observed in the photo.

Alan
 

[GM Canada]

My fat bike of all things had lawyer lips on it. I was surprised but that. Here I am describing what they are and how to deal with them.

https://youtu.be/Tzh2XpBFjJ0?t=7m1s and more detail later in the video here https://youtu.be/Tzh2XpBFjJ0?t=13m10s

You should definitely use two good torque arms. We use these from grin. https://www.goldenmotor.ca/categories/Parts-and-Accessories/Torque-Arm/ . I believe they are better than anyone else's. Each one of these front torque arms also comes with the c-washer included in case it is needed. If you only put a washer on after the c-washer the axle can still slide out of it. Use torque arms properly and you can hold the axle in securely. I have found with c-washers you need two torque arms as one side can still slide out with one torque arm.

Be careful as some torque arms out there look like they won't even do anything. This is something you need to do correctly to be safe.

Gary