MP5 Axle torque problem (even with 2 torque arms)

[Guyblat]

Hey,

So this is the second bike I'm building for myself from the Magic by 5 rear hub motor, 1000 watt.

I have 2 very high quality torque arms as you can see in the picture and I have not needed to file away any of the dropout material, yet
 
The regen is wreaking havoc on my setup for some reason even though this is very similar to the setup I have on my other bike.

Is my main nut not tight enough?

PLEASE HELP!

How can I make the axle stop "thunking" around?

Also it might be helpful is if anybody has an accurate foot pound spec for the 44 millimeter axle nuts?

*pics attached

Guy

[Bikemad]

Something is obviously not tight enough, either the nuts and bolts holding the two parts of the torque arms together, or the main axle nuts (probably both).

I would try cleaning the two clamping surfaces between the torque arm components and then apply superglue or Araldite etc. between the two parts before fully tightening them together with the nut and bolt:



If you can try to preload the torque arms (remove any play in the axle slot) so that one is holding the axle tightly in the forward direction of rotation and the other is holding the axle in the reverse direction of rotation. This way they should be able to prevent axle movement when going from power to regen etc.

If these parts are permanently glued together (or ideally welded together) in the correct position, the axle cannot come out of the dropout, as it can only come out of the dropouts if the two torque arm pieces (on both sides of the axle) actually move in relation to each other by pivoting on the clamping nut and bolt.
The two pieces of the torque arm can be removed as a single item in order to remove the wheel when necessary.

The torque arm clamping bolts and the axle nuts need to be tightened as tight as possible without stripping the thread.

Check out this post regarding the axle nut torque.

Alan
 

[Guyblat]

Thanks Alan!

[Guyblat]

This is driving me absolutely crazy!

I have tried everything I know.

I have tried pre-tensioning the torque arms, no luck.
I have tried filing the dropouts deeper into the frame so there is more surface area, no luck.
I have tried dropping regen down to 25, little luck.
I have tried tightening the bolts to spec (even the main nut to 55nm!!
I have not yet glued the torque arms together, because the tolerance in the torque arms are such that that won't help I don't think.

There is still a small CLUNK (the axle shifting back and forth) but only when I switch from regeneration to acceleration. This is a huge problem and will probably lead me soon to disable regeneration altogether!


HELP!

Cheers

[Bikemad]

This is driving me absolutely crazy!There is still a small CLUNK (the axle shifting back and forth) but only when I switch from regeneration to acceleration. This is a huge problem and will probably lead me soon to disable regeneration altogether!

If the torque arms are correctly fitted with sufficient opposing preloads and the axle nuts and torque arm bolts are tightened sufficiently, then the axle should not be able to twist in opposite directions.

Are you sure it is the axle that is moving within the frame dropouts, or could it be the stator moving in relation to the axle?

Check out this poor quality video which shows my front Smart Pie (with the axle clamped securely in a bench vice) exhibiting the same clunking noise that you have described.



The controller (and stator) movement shown in this video was due to excessive clearance in the stator's keyway slots where it located on the drive key in the axle.

However, if your clunk is being caused by the axle moving relative to the frame, you will have to either tighten the axle nuts to a higher torque setting (if possible) or possibly fit some additional torque arms.

I have not yet glued the torque arms together, because the tolerance in the torque arms are such that that won't help I don't think.

My suggestion to glue (or preferably weld) the two parts of the torque arm together was to prevent the torque arms from pivoting on their clamping bolts due to the tremendous axle torque, as any pivoting action would allow the axle to simply twist itself right out of the dropouts during regenerative braking. 

Just out of interest, I have guestimated the distance between the centre of the axle and the centre of your torque arm clamp bolts as being ~40mm, and can easily calculate that this would produce a pivoting force of ~127kg trying to directly pull the axle out of the dropout with just 50Nm of axle torque.

The only thing counteracting this pivoting force (apart from the weight acting directly upon the axle) is the frictional clamping forces between the two parts of the torque arms, combined with the frictional clamping force of the axle nuts acting upon the contact areas on each side of the two frame dropouts.

Alan