VECTr – Variably Expanding Chain Transmission

In the last post, I said that I had been focusing my attention on a 5-arm 110 BCD version of VECTr that used the same idea for the locking pin as the version in the video.  That basic idea consists of the locking pin moving laterally when contacting the control plates to unlock the gear segment, and being pushed along the contour of the control plate into its new radial position as the crank turns.  I had said that I had been trying to get this to work, and the fact that I was trying, meant that I was unsuccessful.

Old version of control plate mechanism, with long sweeping outside plate (on the left).

Well, it’s a funny thing about tinkering that sometimes ideas strike you while trying to do something else. When I was working on the laterally locking pin design last spring, I was indeed unsuccessful, and so went back to the drawing board (or CAD program) and came up with perpendicularly drawn locking pin design.  And in the fall, I was trying to get this new design to work, when, seeing some parts from the old design on my desk, I wondered again why it wouldn’t work.  So I reassembled them, but tested them with the control plates for the new design, and what to my wondering eyes should happen, but the hybrid of old and new worked (sort of).  I discovered that it wasn’t the lateral locking pin that was the problem, but the control plates (which seemed necessary for the version in the video and had worked there — see image to the right).

Instead of the long sweep for the outside control plate, the new design had two simple angled control plates, but they seemed able to unlock and re-position the gear segment of the old design, but not as smoothly as they should.  So, as a result, for the last few weeks, I have revived the old design and tested various shapes for the control plates.

Finally, I found that by modifying the inside control plate from the old design, it would contact the locking pin on the gear segment at an appropriate angle to unlock it and slide it to the desired radial position.  (It took much trial and error to find the appropriate angle — a better understanding of geometry and the physics of friction might have led to a good design, a priori, but what can you do . . . .)

Gear segment being moved to the outside of the expansion arm by contacting the new inside control plate.

The gear segment in the new outermost position with its locking pin released to lock the gear segment in place.

So, this is (hopefully) the last major hurdle to finalizing a truly functional design.  I know of many smaller hurdles and tweaks that will be necessary, and I will probably discover others, but I feel good that VECTr is getting closer to the marketable stage.