I am in the process of machining the components for several sets of the Crazy Arms adjustable cranks. In about a week or two I’ll have them welded up, painted (navy blue) and ready for shipping.
I have changed the configuration since I made the annimation.
These current sets are made to adjust to 120, 125, 140, 150, 160, 175 and 180mm (rounded off to nearest 5mm)
This is the set I am currently running (unpainted) on my Radial 360, I have ridden the Tour de Cure and about 100 miles since installing them without any problems. In the photo they are at the 140mm setting.
Because of the large amount of hand work involved in making these sets, the price will be $150.00 (U.S. Dollars) each. I will include free USPS Priority Mail shipping to the continental 48 states. Outside the continental U.S.A I will have to add the actual shipping costs to the price.
Radial 360 and pedals in photo not included, (I know it sounds stupid but I have to say that.)
what are the advantages of this sort of crank?
it looks like to me that the pedals rotate around another axis at the end of the crank arm… what good does that do?
these are super interesting and i’d like to know more.
you lock them into different positions, they don’t just randomly roatate around the end. depending on where you lock it, the effective crank length is either increased or decreased.
I have gotten all of the short excentric arms made, here is a pic of them being painted.
I have the square taper and the clamping mechanism for the long concentric arms all made up too, I only need to cut the square tubing for the arm extension and start welding them together. Then some final fit and finishing and they will be ready to go.
I only have one problem the cranks wont match up, if you watch the video, one crank on one side goes down to the side, which the other goes up to the side, if you could make them both go up to the side, this could be a huge breakthrough, because if would be almost impossible while landing tricks to have your ankles ripped off, though the cranks probably arnt strone enough for tricks.
…what are you talking about? Look at the picture of the Radial, they should work exactly as they’re said to. I’m sure it wouldn’t be a good idea to use them for “tricks,” they are square-tapered (right?) afterall.
I would buy a pair, but $150 is WAYY too steep of a price in my opinion.
Yeah, I paid $180 or more (can’t remember exactly) for my adjustable length Kooka cranks (130, 150, 170) for my Coker.
$150+ for good adjustable cranks is worth it for some people. Usually it’s the adults buying that sort of stuff and not the kids.
Keep in mind that these types of cranks are for Coker riding or maybe 29er road riding. Adjustable length cranks on a Coker can be nice if you live in an area with hills and flats and some Cokerable XC trails. It’s much easier to change the length of adjustable cranks than to change cranks. And changing cranks too much can wear out the taper on the cranks. So it’s best to leave the cranks on the unicycle instead of taking them on and off constantly. Adjustable cranks make that possible.
Cool deal on those Crazy Arm Cranks. But I’ve already got my Kookas and I’m happy with those.
Al, I hope I didn’t saturate the adjustable crank market with my Kookas.
I have Al’s prototype of this crank and they look to me to be a very cool, solid, workable design. I think the price MOST reasonable when you consider the parts and labor going into these. You can literally change your effective crank length in about 15 seconds with no tools. Also if your changing lengths alot you don’t risk wearing out the threaded pedal holes. 2 Thumbs up!!
No worry there. You didn’t make that many. The total was probably around 10 sets I’d guess.
The DaVinci adjustable tandem cranks with the 130, 150, 170 holes have also been available for years for those who wanted such cranks. They’re spendy though at over $200 for the set. A few people have them though.
The existing designs have not saturated the market. There are still riders who could benefit from adjustable Coker cranks. It’s just a matter of getting them to know they are available and them being willing to put up the money.
They do look like a great idea. I am planning on buying a coker as soon as I can afford it but unfortianatly I dont think I would be able to fork out the extra money for your cranks (not saying that they are unreasably prised)
You have to think in tearms of forward and back of the rotation of the wheel, not up and down. It doesn’t seem to make any difference if the pedals are both ahead of the crank or behind it, only that they are both the same, so that they are 180 deg apart. In the 2006 Tour de Cure ride I was about 20 miles into the ride and getting realy tired, I was coming into a hilly section so I set them to about 150mm, I tried to re-mount several times, but fell before I could make one rev of the cranks. I looked and realised that I had both cranks set at the same length, but one ahead of the crank and the other behind.
The set of cranks that Phil has were the frist sucessrul set of these cranks that I made, they are the ones photographed in the annimated video. They had about 300 miles of test use before he got them. On my less than sucessful sets, the components that failed always did so within a mile on the frist test ride. Many times not even making it out the driveway. Many lessons learned before I worked out the configuration that I am now making.
John
Your guess is correct, I am making up 10 sets,
My research turned up a thread from 2004 where you produced a sketch of a set of cranks that adjusted by revolving around a large offset spline that mounted to the axle.
I didn’t find that thread untill after I had already made a working set of cranks, but the idea in that sketch was how I originaly had envisioned making them, I just couldn’t find components to make it from, since I don’t have a million $$$ CNC mill out in my garage.
I’m wondering however, if some kind of mechanism could be made (strong enough) that would allow the forward/back adjustment of the pedal within the crank arm. This way the pedal spindle is always in line with the crank; never below or above the center line.
Almost like a kind of “cartridge” that slides back & forth and can be easily adjusted w/o tools, and can be locked firmly in place. This would probably require the crank arm to be fairly wide to accomodate the sliding cartridge.
hmm
what if you made them clamp a different way, so that they screw into the pedal hole? then you would only need to make the eccentric arms and the clamp?
i have an idea of how it would work.
your idea is good, but i’m just thinking even more simplicity.
If you have a better way to build adjustable cranks, go ahead and make them.
My defending whether or not this is the best way to make these is a moot point, They are already built. Though this idea first surfaced 30 years ago, these are as best as I can tell, the first real life working sets that have been made.
What do you mean by “below or above the centre line”? The crank length is the straight line between the pedal axle and the wheel axle - it doesn’t matter where the actual metalwork goes in between. As long as there is a straight line through both pedal axles and the wheel axle it will feel perfectly normal.
(not saying that they are unreasably prised)