Does your spring hinge hold the roller tight enough on the tire to prevent slipping especially in the high setting?
That's the 64 thousand dollar question I hadn't really considered until an hour ago when I attached this assembly once again to by bike and noticed the force holding motor to tire was less than I expected. Can't say for certain it was less pressure than in earlier attempts, but it was the first time in all this fiddling it occurred to me that it might be insufficient.
And the test ride confirmed it
is too little force. Rotated fine with the wheel while pedaling normally, but pressing the boost button - even in eco mode - had it just spinning against the tire. And this is with rough carpet gripper tape, not the smoother stock stuff.
That's... a setback. I could play a little with front-back positioning of the assembly so that the hinge is at a little greater or lesser angle, but I really don't see this making enough difference. Spring force doesn't seem to be adjustable. When I began this project, I had some concern a door-closing hinge might be too
strong for this application, not too weak.
Well, I have a little over two weeks before we take the bike on tour to figure out & execute a solution, which I
very much hope to do. We can certainly ride without the motor and our route this summer (Toronto -> Ottawa -> Montreal) is pretty flat, but it's just a heavy, inefficient, shockingly slow bike... and I've planned our stops with the motor in mind, covering a little more ground than we're comfortable with in acoustic mode.
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The water bottle cage adapter has slots for 1/2" wide straps, which conveniently seems to be the standard width for hose clamps. I bought a kid which let me cut my own clamps to desired length. It took a few tries to work out to position and orient stuff in this tight space between two cranks and with other neighbors like brake/shifter cables, but once that was solved it was pretty straightforward. As expected, tightening these stainless clamps holds the assembly in place extremely securely. Nothing is moving a millimeter!
The adapter's original velcro-based straps work well for holding the hinge closed, to physically disconnect the motor from the tire, so when I bolted my platform to the adapter I slid one of those straps in between..
I had also drilled a couple more holes in my aluminum platform, to try the standard "clamp to chain stay" method:
but between the cable guides and the irregular welded joint, I couldn't get it to lie flat and securely. Though in theory I now have a more universal hinge/motor assembly - if only I can get it to actually, you know, work! - with both chain stay and bottle cage mounting options, so I could I could move it to my road-ish/randonneur bike.
And trying to get this to work emphasized how shockingly out-of-round this bike's rear wheel is! Had this thing (inadequately) mounted in a position that gave several mm of clearance, only to have the tire rub & get stuck along the platform's edge after half a rotation. Seems like the mounting the motor on a spring/hinge should allow it to follow the contour far better than fixed/rigid mount.
Also want to mention, in case it's useful to anyone attempting something similar: there's plenty of places who will laser cut aluminum (or stainless, etc.) and would've done a neater job than I managed, and saved me acquiring a few tools. I chose to DIY to have more control over the timing: I was getting nervous about having everything finished before our end-of-June trip. (Of course I remain nervous, with still no working solution...)