Gearing - Attempt 1
Updated: Jun 23, 2019
I'm not sure this will work (given the gearing) but I have to start someplace !
I figure that it will be easier if I can the existing rear variator / clutch assembly (in some modified manner) to pass the drive through the gearbox to the rear wheel. I'm hoping the clutch / gearbox will be beneficial / not pose any significant problems... although some math with the ratios indicates a top speed of 11kph !! Hmm... To be frank, I think I'm going to need to re-visit this one BUT, at the current time using the existing variator / clutch assembly is the easiest way to get drive into the gearbox... I certainly can't see any way at all (bar a hub motor) of 'ignoring' or bypassing the gearbox - although I have looked at switching gear ratios within it (costly and of (at first glance) limited benefit !
So, to make a start and fit the new sprocket to the rear clutch ass'y, I stripped down the whole assembly and through-welded the sprocket to the two clutch plates (they will not be needed as the rear section of the variator anymore so...
I started by removing the nut from the splined gearbox input shaft. The clutch bell housing (right hand side in the image above) may then be removed, followed by the variator itself.
A large nut will be visible once the bell housing is removed. If you're planning on doing this yourself, then be VERY careful stripping the variator - it's under pressure from an internal spring (image below). I held the variator plates shut (their natural position under spring tension) and removed the large nut. In doing so the spring tries to release - keep that pressure applied, remove the nut fully and all comes apart as per the next image.
I then stripped the variator guide plates from the shaft and welded the 69tooth sprocket to both plates. To ensure the new sprocket remained central / true I made up a plastic space (again, using Sketchup and the 3D printer).
Reassembly was the opposite of disassembly (above) - apply pressure to the spring and start the nut off on its thread. Lock up the nut and refit the whole assembly to the gearbox input shaft.
If I find (as I'm pretty sure I will) that the clutch assembly is just too inefficient / isn't needed then I can always lock the clutch. I can also lengthen the gearing somewhat...
But... that's for another day !