Kevin Crockett - VK3CKC
Ah, the sweet, sweet, smell of success. Got a rough lash-up clamped down in various places, sufficient to give a validation test. It worked. You just move the slider until the change takes place. A visual indication to the rider might be a noticeable change in the resting angle of the chain tensioner.
I used a 14t-28t 5-speed mid-drive cassette mated with a 28t-48t triple chainring. Used derailleur idlers were used for the change slider and the chain tensioner. The chain guide idlers were substituted by a length of 3/4" pipe.
Larger idlers might be required for the slider and chain tensioner use. Their positions relative to anything else may need fine tuning.
The height of the slider idler must be higher than the height of the bottom of the smallest cassette sprocket. This will automatically make it higher than the bottom of the largest sprocket.
A triple chainrig might be used in place of the Hilgo double but it would probably be pertinent to bypass it in operation to avoid overlapping gears. A spreadsheet showed that the gearing should be sufficient with only two chainrings, providing a low range and a high range of gears, selected as required for either hill climbing or flat/downhill riding. The ratio between the mid-drive output and the rear wheel sprocket (only a single required) could be selected for even higher or lower overall gearing.
All in all, it seems like a great idea and one that I will be looking at incorporating in my current trike build - with an 8 or 11-speed of course.