The rear cassettes on a bike traditionally spin a tire around a stationary axle. The wheel spins, but the bolt doesn’t. To drive the Falcon, the cassette and axle must spin together. We needed a new way to secure the cassette/axle to the bike frame.
My last attempt did not shift very well, was very difficult to align and ugly, so so ugly. Because I used u-bolts to secure it, that required the plate to be very large.
This time, my idea is to use the outline of the bike frame’s rear fork to keep the bracket oriented correctly and locked it into place with a single bolt through the fork’s mounting slot. I traced the outline of the rear forks onto graph paper and scanned the traces.
I pulled the scan into Fusion 360, scaled it up to match the size of the graph paper grid, and used that to model the basic bracket in 3D.
I decided I should test the fit of the bracket before making it in metal. Printing the model in plastic first saves me some money and a lot of time, especially if it takes multiple iterations to finalize the part.
After I finalized the fit of the bracket on the rear fork, I had to figure out where to hang the rear derailleur. It took a few tries to get it in the correct spot. For the first try (blue in the image below), I put the mounting hole where it would go if I wasn’t using a giant low gear (52T). I am, so it had to be lower than that.
The second try (black in the image below) was technically correct, but the derailleur was lower than I wanted, especially for the mud. I had also added the profile of a derailleur hanger but I placed it on the bracket backwards.
For the third iteration (white in the image below), I swung the mounting tab forward 90 degrees and flipped the tab stop to point counter-clockwise. I also flipped the bracket front-to-back to get the derailleur a little closer to the sprockets.
Everything went together surprisingly easy.
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Though the test assembly is working nicely, the bracket still needs one more modification. The derailleur rotates forward too much when shifting, so I need to rotate the stop on the bracket 60 degrees counter-clockwise.
The co-pilot’s bike frame is different than the pilot’s, so I need to modify the bracket to fit the outline of those forks. After that, the brackets can be made in aluminum. However, if they hold up during tests, I may just leave them in plastic.
