Well that was an unmitigated disaster.
I got my new tensioner today. It's pretty sturdy, but it's surprisingly (to me at least) small! Here's a (rubbish, sorry) picture:
2016-09-16_09-24-45 by
duncancmartin, on Flickr
It's about as long as the arm on my junk derailleur. So I tried to work out how to attach it in the right place, shortened the chain, and generally realised that I can't use it on the mounting point very easily, and I need another one (or a fixed jockey wheel) to make the tensioning work.
Then I tried to put a second roller on my existing mounting side by side so I could change the route of the return part of the chain. The central part of it wouldn't slot on properly, so I hit it a few times with a hammer to push it on. Then I realised that the bolt had moved in the tube, I hit the bolt, at which point my welds failed.
This was another weld I made when the tip on my welder was not working properly - I will have to check back and make sure there aren't any others (I think I've broken the only 2!).
2016-09-16_09-24-56 by
duncancmartin, on Flickr
Right now I feel like recycling it!
So, I have 3 options (some with sub-options):
1. Carry on with my current jackshaft design and work out how to fix the chain tension issue.
2. Change over to a different jackshaft design that uses a freewheel/cassette and so has a mounting point for a derailler for this chain - this means abandoning the theoretical ability to attach a motor to the left hand side of the jackshaft.
3. Give up on jackshafts. Weld the roller bolt back onto the frame, ditch the jackshafts and just run the chain front to back.
3a. Leave the rear wheel alone - this will give me really low gears (when I eventually sort out the front mech to shift chainrings) - something like 21 inches to 71 inches with the current rear wheel.
3b Get a new screw on freewheel (11-28 would give 21" to 90"). Also needs a new shifter as my current one only has 6 gears in index mode.
3c Build a new rear wheel on a decent hub meaning I can get whatever gear ratios I want. Means I need a new hub, spokes, rim (can probably re-use one I have) cassette, shifter and maybe derailleur.
I've got stuff I need to do this weekend, so I probably won't have much time to work on it. Will consider my options. I'm kinda fed up of it now, I want to ride it (and start on my next build - a Spirit mid-racer recumbent).
Cheers
Duncan