VECTr – Variably Expanding Chain Transmission

So, since having the patent issue for VECTr, I made another model/prototype with which to conduct tests to see how it performs on an actual bicycle while bearing the (rather considerable) loads of an actual rider (me). The first step in order to do this was to switch out the bottom bracket on my Trek mountain bike with a 127.5 mm one so as to accommodate the somewhat larger size of VECTr. That took getting the appropriate tools and doing a little research on how to loosen the original one which seemed good and stuck. However, having successfully completed the bb switcheroo, installing VECTr was pretty straightforward.

Once I fashioned a new, compact controller, I set about testing its operation on the bike while it was supported on a repair stand.

The test showed VECTr operating amazingly well!

The demonstration video (below) shows VECTr in action mounted on my bike. It is operated using a lever/friction shifter, so the shifts are not as precise as they would be with an index shifter, but, as you can see, they do not need to be for VECTr to change gears as quickly and efficiently as a derailleur/chainring system.

The next step was to take it on the road to see how it handled operating under load. This I was able to do this week. Again, VECTr performed remarkably well, and showed the current model very nearly to be a true prototype and in need of relatively little refinement to be production ready. I don’t have a video of road testing as it would require a frame-mounted camera to show anything interesting, so that will have to wait.

But, there were some specific findings that did emerge:

• Bore loads well. VECTr was able to bear what I thought were moderate loads in the higher gear settings. I did not try to climb any significant hills, but VECTr performed well in the minor inclines and slow rolling starts of road riding. Obviously, I have no quantitative data – just my brief but real riding experience.
• Compatible with rear cassette gears changes. VECTr was able to continue working even as the chainline varied with the changes in gear on the rear cassette.  I had not tested this on a model before and feared the varying chainline would prevent VECTr’s gear segments from engaging the chain without a chain guide. Such a fear turned out to be unfounded. Below is video of VECtr operating as the rear cassette changes gears with the bike on the repair stand.

• No chain slippage. Critics often predicted that since VECTr has isolated points of contact with the chain, the higher tension on the chain at those points would cause the chain to slip, undermining the central task of a drive train. This did not happen.
• No “lumpiness.” I did not feel any unevenness (or “lumpy” feel) in the pedaling. Some critics predicted that pentagonal path the chain formed while being driven by VECTr would result in such a lumpy feel, but I could not discern any. A more sensitive cyclist perhaps might, and precise power or torque measurements would probably reveal non-uniform results.

A couple of negatives:

• I need to design and have machined a more sturdy and robust controller, as the operation of VECTr tended to drive the controller out of alignment and distort the frame-mounting bracket.
• I need to utilize stiffer, yet smaller springs for the locking pins on each gear segment. Occasionally, a gear segment would not lock into place and slip inwardly under the force of engaging the chain. This was often rectified on the next pass through the controller and VECTr would continue to function properly. But a few times, the gear segment slid to where it could not engage the controller effectively, which pretty much prevented the pedal crank from turning. Using springs more appropriate to the space constraints of the gear segments should fix the issue. I expect this is an easy fix.

Over all, the positives of

• a lighter,
• more streamlined sprocket-mounted gearing system,
• with more gear settings and
• as reliable (or more so) than chainring/derailleur system

more than outweigh any negatives associated with the increased complexity of VECTr.