VECTr – Variably Expanding Chain Transmission

Despite the dearth of posts on VECTr, progress has been proceeding, albeit in fits and starts. (I have been making some major transitions in my day job, too,  over this time.)  Encouraged by the interest in the original video of VECTr’s operation (which now has over 12K views), I sought to refine and simplify the design so as to make it more feasible for me to conduct a first run at manufacturing it commercially.  I also tried to take into account suggestions for making it more compatible and smoother in its operation.  In the weeks ahead, I will be detailing the improvements I made, designs I tried, and challenges I encountered in these past intervening months.  I will also be giving updates on the state of the current design and progress in testing it, hopefully continuing to move toward the point of making a salable product for widespread use.  Stay tuned for further updates!

Thanks to all of you who have visited the original VECTr video on YouTube. Our number of visitors has now exceeded 10,000! Check out an updated version of the video here: https://www.youtube.com/watch?v=fVFmUcA6sjc.

So a bike blog, The Retrogrouch, makes passing reference to VECTr while showcasing another device (the Wavetrans) to show that expanding chainring devices are nothing new in the history of bicycle transmissions.  After noting the coolness of its various features, the Retrogrouch asks, quoting the  Wavetrans website:

You know what else is cool about Wavetrans? It’s ‘something . . . that you have never seen before.’ . . . Unless you actually know something about bicycle history, that is. In which case you know that these things go back almost to the beginning of the safety bicycle.

If you’ve read prior posts of this blog, you’ll know that the insight that expanding chainrings are nothing new, is itself nothing new.  I pointed out in a post on August 30 (here) that this had been tried for over 100 years, but that most of these devices tried to expand the whole circumference of the chainring all at once, which seems to be impossible given that the links on a chain cannot stretch.  The realization that changes in the chainring’s radius would have to occur when the chain is not engaging led me along the path to VECTr.  The Wavetrans inventor seems to have made the same discovery.

If you look at the prior designs over the last century, you will notice how massive and complicated they look.  And with mass and complication comes weight and expense.  This seems to have been the demise of the previous admittedly ingenious designs.  Retrogrouch draws this moral from his history lesson:

Something tells me that people today are no more likely to adopt a transmission that’s heavier, more expensive, and more complicated than a derailleur system than they were 20, 30 or even 100 years ago. I just don’t see the Wavetrans (or the VECTr, or any other similar ideas that might be brewing out there today) having any more success than their Victorian-era counterparts, or any of the revivals from the ’70s and ’80s.

The claim that the idea of an expanding chainring has been tried and failed is the most common criticism I have received about VECTr. I am somewhat surprised and disappointed that this is often the first reaction of the more serious bike enthusiast.  I would not have thought this was so conservative and staid a group.  They seem to reject new ideas, or new attempts to make old ideas viable, because they are not the now current standard.  Never mind that what is now old, was once new.

VECTr is truly worth its weight . .  and worth the wait!

The only really relevant question is whether the new/old device works and is worth what it costs. And cost is measured, for bicycles, both monetarily and in weight.  Prior expanding chainrings failed because they were not reliable enough given their price and weight. Retrogrouch seems to assume that every one must be heavier, more expensive and more complicated than current double or triple crank sets.  That looks to be true of Wavetrans, but not of VECTr.

The weight of the current version of VECTr  (in steel) compares quite favorably (500 g) to the triple chainring (Shimano Alivio (in zinc?)) and derailleur it replaced (475 g).  When VECTr is commercially manufactured, I am sure its weight will be reduced.

When compared with other in-line transmissions with regard to weight versus cost, VECTr is clearly superior:

As far as reliability and performance, the jury is still out on VECTr as I am still tweaking and testing the design.  Again, it is supposed to outperform triples in having more gear settings, and in maintaining a consistent chainline.  It is more complicated (six moving parts) than triples (one moving part (the derailleur) and three relatively stationary chainrings). But that should be offset by the greater reliability of preventing dropped chains.

So, no, an affordable, light expanding chainring has not been tried.  VECTr truly is something you have never seen before.

On Friday, my lawyers (it seems odd to say that) filed my application for a patent.  This was a long process that started way back with the CABT design.

After all the design work to simplify an expanding chainring device, I  built the VECTr model and was able to get it working.  I then updated the provisional patent application I had submitted on the CABT (which in the year following its filing had lapsed) and submitted a provisional application on VECTr. This allowed me to claim “Patent Pending” and provided a year’s protection (provided a filed a non-provisional application) to show the working model on this website and solicit feedback, and eventually offer it for licensing to prospective manufacturers.  Since there was enough positive feedback, I thought the design might be commercially viable, so in June I started working with a lawyer I met through an Eagle Scout networking event.  Producing a description of VECTr and its functioning in the appropriately arcane legalese, along with other possible ’embodiments’ proved a long and tedious process.  I had to apologize to my wife for I learned it really is hard for others to understand the details of VECTr’s workings which I discovered from having to explain it to the lawyers.

Well, that long, laborious process concluded Friday with the filing of the patent application.  Now I expect there will be a longer, more protracted process as the patent office reviews the applications, and requires clarifications.  I will keep you posted on the progress.

Last week, I blogged about working on the mechanism within VECTr that will multiply the relatively short distance (4 mm) that a Shimano index shifter pulls to the greater distance (11 mm) of the VECTr settings. This is a critical part of the VECTr gear that will make it compatible with existing index shifters, such as a Shimano 7-setting shifter.

This morning, I was able to make this mechanism work! The working model in the video is rough, but it gets the job done with the shifter…

https://www.youtube.com/watch?v=7OhGLS7lhSk

This week, I have been working on the mechanism within VECTr that will multiply the relatively short distance (4 mm) that a Shimano index shifter pulls to the greater distance (11 mm) of the VECTr settings. This is a critical part of the VECTr gear that will make it compatible with existing index shifters, such as a Shimano 7-setting shifter.

Work in progress

After realizing that the Continually Adjustable Bike Transmission (CABT) model was just too cumbersome to be appealing, I could not let the idea go. I still thought the problem of an expanding chainring system should be solvable, but it would take a new approach.  As my wife will gladly tell you, I am often guilty of over thinking things and making them more complicated than they need to be. So, I ditched the CABT design and started over from scratch.

I tried to think of the simplest way to get the gear segments both to be adjusted (i.e., change radial position) and  to lock into that new position. First, I decided that having gear segments slide along straight arms radiating from the center of a circle was the simplest way to for them to change radial position. (This is far simpler than my use of spiral-shaped gear segments being moved by a pin sliding within them, which thereby changed their radial position).

The other problem was how to allow them to lock into position while engaging the chain, and unlock and change position when the bicycle’s rider wishes to change gears. I got rid of the threaded screws that changed the position of the gear segments in the CABT model. I went through several designs for the locking mechanisms and tried building and testing them, using simple materials and working in my garage.

Initially, I thought the gear segments could be locked by means of a toggle which fit into a notch on the edge of the radial arms. I tried simple pivoting brackets, and an elaborate scissoring mechanism:

Toggle locking mechanism

The another design involved having pins pinch the radial arms when depressed by the force of the chain:

Pin locking mechanism

Neither of these seemed like they would work sufficiently well, and they were too complicated. So, I thought it would be most feasible to have a pin perpendicular to the plane of the base plate serve as a locking mechanism.  I thus had to figure out a way for this pin to move in and out as directed by the rider:

Perpendicular pin locking mechanism

Next, I tried a design inspired by clothespins:

Clothespin-inspired locking mechanism.

After that, I tried having the toggle swivel when making contact with the control plates, which would raise the locking pin from its notch:

Swiveling toggle locking mechanism

As many designs as I came up with and tried to build, they all seemed too complicated and/or heavy to be commercially feasible:

Not it either!

It wasn’t until I thought of putting the locking notches within the groove along which the gear segments slide that I made the step which led to VECTr in its current design:

The penultimate design

After realizing that the gear segments had to be able to change radial position during the quarter of each revolution when they are not engaged in the chain, I also saw that I still had to work out the mechanics of how the gear segments would move. And this required framing the problem in a new way yet again.  Now the problem was: how can the gear segments change radial position when they are free from the chain, yet maintain their new position (and not slide inward) when they do engage the chain?  The problem was how to make the gear segments move when the bicycle’s rider wanted them to, yet remain fixed so as to serve as an effective power transmission.

CABT drawing

My next bright idea was to use long bolts radiating out from the center of a base plate, and affixing on them specialized nuts which would slide in a groove of the gear segments.  As the bolts turned, the nuts would be driven inward or outward, and the gear segments would expand or contract.  The turning of the bolts would occur as wheels on their outer end rubbed against control plates suspended next to the bolts as they pass the plates on each rotation of the crank.  Thus, depending on which side of the bolt rubbed against the control plate, the bolt would turn clockwise or counterclockwise, and the gear segment would pivot outward or inward.

Original CABT working model

Combining these ideas, I designed a device called the Continually Adjustable Bike Transmission (CABT) and set about trying to build and test the design.  After even more effort and many trips to hardware stores, I built a working model of that design.  I was quite pleased and excited that the CABT worked.  I even filed a provisional patent application and tried to interest various bicycle component manufacturers in licensing it. Unfortunately, I found no takers.  An engineer directed me toward Frank Berto’s book, The Dancing Chain, and becoming familiar with the history of the bicycle transmission, I realized that the CABT was too heavy and complicated to be marketable.

Back to the drawing board again. All of us have had to start over at some point, right?

In 2008, I started working in earnest again on the bike transmission. My wife and I had bought a home in the suburbs by now and were both busy with our careers. I ended up working at Sam Houston State University in campus ministry and teaching Philosophy, though the mechanical problem-solving part of me was still largely unfulfilled.  I channeled that desire into the bicycle transmission.

For my part, I kept trying to solve the problem of making a chainring expand by designing a device that had the sprocket broken up into gear segments hinged at one end and simultaneously pivoting them to increase the radius at which they would engage the chain.  As I looked into prior patents on expanding chainrings (and earlier “expanding pulleys”), I found that people have been attempting to solve this problem for almost as long as bicycles have existed.  Frank Berto, on p. 53 of his magisterial book The Dancing Chain, cites the Protean device from 1894 as the earliest commercial attempt to manufacture an expanding chainwheel system. (In another post, I will outline other earlier attempts.)

Examples of historical patents

For over 100 years, many previous inventors had attempted various ingenious ways of expanding a gear’s radius, yet almost all of them involved making all the chain-engaging elements move at the same time. Apparently none of them had been commercially successful, however, since none of them were available today.  And my own limited tests with the crude models I could construct seemed to indicate that there was a problem in having gear segments move or expand simultaneously.  While distance between the teeth of the gear segments remained fixed relative to each other, the distance between the gear segments (and so the teeth of adjacent gear segments) would change while the pitch of the chain would not.  (To address this issue with VECTr I recently made a particular refinement to my present design.)

This new insight into the limitation of the idea I was pursuing allowed me to frame in greater specificity the expanding chainring problem: how could the radii at which the gear segments engage the chain grow or contract while still fitting into a chain whose links did not vary their pitch?  In one moment, while driving down a back road in Central Texas, the idea hit me that the gear segments could change their radial position (in fact they would have to do so) only when they were not engaging the chain.  I realized that on every turn of the crank, there was a quarter of the revolution when the gear was free of the chain.  This is the space between where the chain comes to the chainring from the rear sprocket and where it leaves the chainring to return to the rear sprocket.  It had to be in this quarter turn of the crank that the gear segments could change position without hindrance from the chain, but they could still engage the chain with properly pitched teeth.  This flash of insight sent my design of expanding chainrings into a new direction, one that would ultimately culminate in VECTr.