Hi Karl you indicated a chain length of 600mm which is nowhere near the length required to go from the bottom 12T 12mm bore sprocket to the upper 28T 8mm sprocket. I got a 1.5m length thinking I would simply split that for the 2 pedal units but discovered that it used approx 925mm to go around both sprockets and distance between the 2 shafts but was quite loose and with the slack would cause the non loaded length of chain when winding to jump off the sprocket teeth. I shortened the chain by 1 outer and 1 inner link so the joiner would match again and was 1 tooth too short impossible to tension and rejoin the chain at all.
A possible solution could be to use a simple 3mm angled aluminium bracket with 2 roller bearings fitted on the vertical face and act like a chain derailleur tensioner just below the upper sprocket. The bracket simply mounts to the existing 2 screws that are used to secure the rear flange bearing. Am making a prototype and w ill post a pic if it once fitted and if it works or not
Hi Karl here are a series of pics what I have put together but yet to do final test in completed unit. I cut a 70mm wide section of 100x50x3 alloy RHS which I then cut on the corners to give 2 right angle brackets. The 100mm long side allows enough excess to cut a 30mm flat plate which might have to be used to stiffen the roller screws as a brace if required.
I then cut 3mm off where the Rear Flange Bearing mounts (Upper Rear Body section) to allow the angle bracket to fit flush under the bearing mount and keep the threaded rod aligned correctly
Matched the screw holes in the angle so the flange bearing screws down on top of the bracket and clamps the angle down underneath
I printed a couple of 30x11x6mm rollers to test as chain tensioners with a distance of 30mm between them which seemed to be a suitable amount of squeeze on both sides of the chain to remove the chain looseness from the bottom sprocket to the top sprocket and positioning them just below the top sprocket
I used a socket head screw and threaded the bracket for them to screw into and put a nyloc on the other side so the Rollers are able to spin freely on the screws. The rollers help to keep the chain fully meshed on both top and bottom sprockets without jumping off the teeth no matter which at direction the sprockets are rotated
UPDATE: this has now been tested in the complete pedal assembly and does what I hoped and works quite well.
Good morning! I am now back in the driving seat, I have been away for a couple of days visiting family. I have corrected the chain length to 1m per side in the guide. Let me know how your tensioner goes. I do not have the pedals infront of me until Oct 12th. So feed back will mostly come from yourself.
Kind Regards, Karl