Adjustable crank idea

He he, One crank to rule them all!

One problem with the Power Cranks design is that the access to the adjusting bolts is on the back side of the cranks where it would be hard to reach on a unicycle. Fortunately, the spokes on a Coker wheel are spaced widely so you could still get your hand and tools in there, but it would be better if the bolt heads were on the front side of the crank.

I also don’t like that the Power Cranks design has that protrusion that increases the Q-factor. That kind of protrusion could throw your foot off the pedal if your foot wanders over next to the crank. At high RPM that could result in a high speed UPD.

I much prefer a design that doesn’t have a protrusion that can knock your foot off the pedal.

Re: Adjustable crank idea

On Sat, 24 Jan 2004 13:23:28 -0600, Mikefule
<> wrote:

>Borges wrote:
>> Short cranks:
>> hub
>> <>
>> pedal
>> Long cranks:
>> hub
>> /
>> /
>> pedal

>I saw this idea floated in this forum in relation to a suspension

April 2003, Andrew Carter.

Klaas Bil - Newsgroup Addict

I have a feeling you might need two points of contact with the ground for such a thing to work? Or at least training wheels on the front and rear. - John Foss commenting on a picture of a one-wheeled vehicle he saw on RSU.

I have two pictures of such a thing. Here’s one.

Klaas Bil

1 Like

The next question is what we’re going to name these cranks. The credit should go to Dave, John, and Steve, but that’s a lot of names (or initials) to put together.

Re: Klaas Bil has attached this image

I want one!

Is exactly what I was thinking of.


That is a truly beautiful machine.

The picture that Klaas posted is from a gallery by Lars Lottrup. See the thread A new unicycle in China for the source.

Here’s a link to Lars’ China gallery:

The thumbnails for the hoop wheel giraffe are not in the gallery but the pictures are still there if you know the links:
Hoop wheel picture 1
Hoop wheel picture 2

And it is a beautiful unicycle.

In fairness to Dave, his design was a garage mod of existing parts. A clean sheet of paper design using the same principals woudn’t have these problems, and might turn out to be lighter and easier to work on.

As Ben’s post pointed out, there is quite a bit of room for improvement on both designs. I’m thinking of them as only examples of a whole family of spline-based bent-crank designs. Time will tell which way is best.

Build a little, test a little, build a little, test a little…

I was thinking about Steve Howard’s rendering of Onewheeldave’s crank. Steve has the short piece next to the pedal and the long piece attached to the hub. I think it would make more sense to have the long piece attached to the pedal and the short piece attached to the hub.

The way Steve has it, the short piece is in a position where it could knock your foot off the pedal if your foot gets too close to the crank. If the long piece was next to the pedal then that couldn’t happen.

I have a bad habit of letting my feet wander in and get close to the crank as I ride. A crank design that doesn’t penalize me too much for that sloppiness is preferred by me.

Another option (I mentioned this before but didn’t explain it too well) would be to have the section of crank that connects to the pedal to attach to the inside (i.e. side closest to the wheel) rather than the outside (as it does in Steves rendering) of the hub section of crank.

This would necessitate a small extension where the pedal connects to its crank section, which would lieover the top of the other crank section when in ‘short’ mode.

The advantages would be that the pedals would be not wider apart than with standard cranks, and the problem that John mentions of foot hitting crank wouldn’t happen.

I’ve modified the two cranks based on what has been written since my first ideas were presented.

I liked John’s idea of making the long part on the splined hub connect to the pedal rather than the axle. I further modified it by making the arms slightly thinner (they were over designed to start with I think) and making the splined connecting shaft hollow. Doing this removed some serious weight … Dave’s splined crank now weights .72 pounds each and is adjustable from 120mm to 180mm.

John’s eccentric crank has been lightened too. I haven’t done any real analysis but I think this crank would be VERY strong because of the wide cross sectional area and large diameter hub. I removed a bunch of material from the hub and cranks bringing the weight down to .65 pounds each! The eccentric crank is adjustable from 125mm to 175mm since I was able to tweek the center distance a little farther apart from the original design.

I’ve created a gallery so the jpeg’s could be larger for better viewing. It’s located here:

When I created the original crank pictures I mated them to a standard hub. What was I thinking? This latest pair of pictures shows the two crank designs mated with Harper’s geared hub … enjoy and keep the ideas coming!

Steve Howard

They’re beautiful images, I’m really impressed.:slight_smile:

A stepping stone between an idea and an actuality is a visualisation, so let’s hope that someone with the means to make these is inspired by the images you’ve made.

Also, looking at the image of my bent crank design, I reckon John’s idea of reversing the two crank parts is definatly an improvement.

Agree, these are beautiful. What CAD package are you using?

A couple of recommendations;

On Dave’s design, having the spline fit in from the wheel side makes a lot of sense. I was going to suggest something similar but Dave beat me to it. The crank can be bent in an S to bring the pedal attachment point out to be flush with the end at the hub.

On the ecentric design, I’d put a hinge in so that this can be opened and closed around the core part and closed with the “ski boot buckle.” It would make changes a bit quicker. Though I’m having second thoughts on the quick release buckle. If it catches on something and comes undone that could be a mess. It would need some form of safety to prevent inadvetnent UPLOCs. (UnPlanned Loss of Cranks)

Oh great; more speed options. This is becoming as complicated as a 21 speed bike (with as many parts that could break).

Steve, as the parts now stand how hard would they be to actually build? Would they be a manufacturing nightmare, or are they still simple enough to produce (on a mass-scale or on an individual level)? I know we’re in the design phase right now, but I’d like to know about practicality.

My solid modeling software is Autodesk Inventor.

Yes - that would result in no offset but the long part wouldn’t be able to fold completely over the short part because it would contact the spindle (axle) so the range of adjustment would be limitted on the short end.

Not too tough. The part that would be the most difficult for me to deal with is the tapered square hole. Dave’s design made to fit a KH splined hub rather than a square taper hub would be pretty easy to make. The eccentric design wouldn’t be too bad either except for the square taper.

Back to the CAD software …

I’ve saved the two crank designs (and Harper’s hub) as solid models that can be downloaded and viewed with a free viewer available from Autodesk. The idea is that anyone can download and install the viewer on their PC, then download my models to view them with the ability to zoom, pan, rotate, break the model apart, view individual parts, see part data and more. The viewer is called “Streamline Viewer” and is available here:

This software requires Windows XP or 2000. The faster your computer is the better.

The solid model files are here:

Get the files by right clicking on each one and do a “Save Link Target As” to download them to your PC.

I know this isn’t real clean but it should work and it’s pretty cool when it does!

Steve Howard

Great work guys…

I’m glad to hear that it’s not too hard to make. For me right now, it’s kind of a toss up between the two designs. I like them both, but they both look a bit bulky.
Form a strength point of view, which design looks better?
I would think that the weight of john’s design could be lowered by cutting out sections of the crank like on some of your frames? I love the way your frames look.

For Dave’s design, I like the way it looks now with the shot section outside and close to the hub. I’d be afraid of hitting my ankles on it if it were outside (think KH crank x 10 :astonished: )

I know this is a seed of an idea, but should we as the unicycling community be worried about someone stealing these designs and patenting it or something of that nature? I’d hate to have these ideas “stolen” then produced by someone who doesn’t know what they are doing then charge insane prices blah blah blah. Public domain would be a nice place for these, don’t ya think?

Oh, one more thing… how IS that production Harper hub coming?

expect more comments later,

The only way to protect your ideas, AFAIK, is to be very secret and to go after patents. Too late for #1, so your recourse is #2. The overall approach you’ve taken (discussing it in worldwide-public forum) suggests that you’re more interested in having the product available than you are interested in having control over how it is produced and who profits from it.


Can those models be viewed through AutoCAD (made by Autodesk, I think)?


given some of the costs involved mentioned earlier on this thread (sounds like a round $5000 just for the paperwork) got me wondering if a patent can be held by a group of people as opposed to an individual
since it seems unlikely (?) that RnD (not to mention patent application-) costs will ever be recouped from this project and that a whole bunch of people seem quite keen on getting their hands on this product, or the product that will flow from this idea, is it possible to ‘pass the hat’ and collect the money to fund such an application?

and given the apparant limited commercial viability of such a product, should we be concerned about protecting the idea at all?

This thread constitutes a documentation of the idea, so unless someone else has previously documented the ideas (with credible witnesses, etc) then Dave, Steve and John have the only shot at locking the idea up. Patent law is set up to encourage free discussion early because secrecy is bad for innovation. OneWheelDave actually took the first step of protecting his idea by posting it. Now the clock is ticking. If no legal action is taken to protect the idea within one year it is considered an abandoned idea and becomes public domain. Patents are not issued for ideas that are already in the public domain, so after one year it’s fair game for anyone to set up shop and make them.

As I see it, OneWheelDave has an original patent on the splined-bent-crank idea. John and Steve can claim derivative patents on an eccentric variation on the splined bent crank. (I’m not sure of John’s chances for patenting the smooth eccentric design since there are already examples of eccentric crank designs in the public domain. He’s got a good shot at it, though, since these have the eccentric bit at the pedal end.)

Strategically, it makes sense to go after one combined patent as I suggested in an earlier post. Three patents would cost from $10-15K; one patent with multiple claims would cost $3-5K. Since the market for the idea is small - probably only long distance unicyclists - it would make the most sense to go for a combined patent based on Dave’s original idea with John’s and Steve’s inovations as additional claims.

So the real question is - who wants to sink $3-5K plus hundreds of hours of writing and re-writing to protect this idea? And if this person (these people) is the owner of a 'cycle parts manufacturing firm, won’t they want to recoup their investment by insisting that Dave, John and Steve sign over their rights and then charge an additional few $ per crank, thus defeating the purpose of patenting it in the first place? This invention isn’t as hot as “velcro”, so there are decisions to be made.