Keeping the drive bracket secure with it mounted to just one side of the bottom bracket does have some challenges. Adding the anti slip material to where the drive mates with the BB face has made a big difference but it still means the bottom bracket bearing cup needs to be very tight to keep the drive secure.
The drive will move on the bottom bracket more easily using a larger and heavier motor. I had very few issues with the 50mm motors but the extra weight of the 63mm motor caused more slippage issues. What I have found is that on shut down, the motor gets driven into the end stop bolt with quite a force. Against the end stop metal bolt, this creates a sharp "jack hammering" action. This makes a bit of an unpleasant knocking sound each time the drive disengages and is constantly trying to rotate the drive on the bottom bracket.
I have come up with a very simple fix for this which i have been testing for about a week now. Here it is:
I simply added 3 #7 o rings to the lower end stop bolt so that the swing arm now has a padded landing point when disengaging.
Firstly this modification has made disengagement silent rather then hearing a metallic clunk every time the drive disengaged. This is a nice improvement in itself. However I think the big advantage will be a lot less tenancy for the drive to move on the bottom bracket due to the reduced jack hammering action on disengagement.
The modification is super simple. Just unscrew the bottom end stop and install the 3 small o rings over the end stop screw. Once done, re set your end stop position to allow for the extra diameter of the o rings and you are ready to go.
All new drives will be shipped with this modification and i will send out o rings to all those that have perchased drives so far.
If you cant wait for my delivey, the o ring only cost a few cents and can be bought through most industrial suppliers.
The part is as follows: Neoprene #7 o ring. 5/32 ID x 9/32 OD x 1/16 Width.
This doesn't mean you cant use the drive as shipped as it works perfectly well. This is just an enhancement to the design.