Cody and I got together today via Skype and began to flesh out the Solidworks model using a mid-drive motor approach. It appears that mid drive is the way to go.
The plan is to place the motor at the same location as the intermediate cluster. It will drive down to the front derailleur which will be a VERY wide range cluster.
This side view shows the chain line in orange, going to the largest cog. (Not showing a 45t cog here.)
One Up Components makes a 45t modification http://www.oneupcomponents.com/products/45t-sprocket-18t to the Shimano CS-M9000 cassette that we plan to use.
This is the Shimano 11 speed CS-M9000 cassette - http://www.ridextr.com/en/productdetail/sku,CS-M9000.html
It is a really light weight design that includes some titanium cogs, as well as a carbon fiber body.
Shimano XTR M9000 Long Cage SGS Rear Derailleur is a great choice for the front derailleur. It can handle the 11-45 range, which gives the motor the most help. It also has advanced ways to maintain chain tension, which is helpful to keep the chain from falling off.
The bottom line taken from the spreadsheet shows the 11/45 cassette. The cool thing is that this gives a low gear ratio of .44, or 8.8 gear inches in low gear, as seen by the mid drive motor. This is a very low gear. Lower than what we have on either the New England Handcycle or Travel bike. It should mean that the mid drive motor can easily power the bike up even steep hills.
This chart shows that in low gear, each crank of the pedals moves you 27 inches. At 50 rpm, the bike is only going 1.3 mph. But at least it’s moving! With a hub drive, the motor would have to put out more than twice the torque because it has a 20 inch direct drive wheel vs a virtual 8.8 inches wheel with the gearing.
Now what about at high gear? Now we use the 1.82 ratio, and at 100 rpm, we get 10.8 MPH.
Can the mid drive motor go up to 150 rpm? That would about do it for speed. I wouldn’t be pedaling at 150 cadence, because of the intermediate derailleur.
Below is a confusing Excel file viewer (I don’t know how to get rid of it.)
Ignore that and go right for the Excel file download at the end.