first the unsuspecting victims
first the unsuspecting victims
notes on pix 2 – the pedal part has small high grade bolts drilled&tapped to prevent that part of the crank from popping off the bracket. And the hub part of the crank has notches ground that the large u-bolts ride in. It ain’t coming off.
On the unicycle:
Oops forgot to comment on pix 3 – those were at the 7.5" setting. What a crazy large pedal circle, feels very strange to pedal (I’m 5’10"). I’m probably going to cut them down and eliminate that setting. That leaves 6.5, 5.5, and 4.5 inches.
Pix of entire rig:
pix 5 - final one!
Pix of the shortest 4.5" setting. There is alot of bracket mass swinging on opposite the pedals, but you don’t notice it, and it doesn’t get close to your leg or frame.
Also note the geometry – I put the crank halves on both sides of the bracket, which results in a pedal-hub outward offset identical to the stock 6" Sun cranks, which I really like. The donor 5" cranks did not have that geometry and the pedals were too close for my taste. And the “outer” surface of the 5" cranks was coplanar, so those flat surfaces sit flat on the bracket, no curved wobbling stuff here. You couldn’t do these CrazyCranks with the Sun cranks because the outer surface is not flat.
The bracket was made by “ripping” a 2x2 steel tube in half down the sides, then trimming it back some. Circular saw with metal cutting blade and a pair of quality hearing protectors. This gave the two shallow-“C” shape brackets. I haven’t cut them down in length yet. The 2x2 tube was some crap I had lying around.
I cut the cranks down and then removed about 1/2", so the shortest size is 4.5".
The u-bolt hardware is cheapo crap. Each side has 3 pedal crank u-bolts, each 1/4" (couldn’t find 5/16 u-bolts, rats, so I used 3 smaller ones). There is also a high-grade bolt that is drilled and tapped to help prevent the crank from pulling away from the bracket. This part of the crank assembly is not intented to be taken apart. I might even tack-weld it.
Each side has 2 hub crank u-bolts, each 7/16". The underlying crank half has small notches ground in it so the u-bolts slip on. They don’t fit without the notches. I don’t see those pulling off.
This could certainly be re-engineered to use fewer bolts, by using grade-8 hardware. And the brackets could be made more accurately, perhaps with off-the-shelf stock instead of cutting up what I had lying around.
Weight? Bah, with both water bottles full, the thing weights almost 19 lbs.
a couple of more final comments
5" Cranks $12
brackets - from the junk pile
What isn’t clear from the pictures is the hub-side crank half is bolted to the unicycle hub just like a normal crank. Then the CrazyCrank brackets bolt on top of those, via the 2 large u-bolts.
Those are CRAZY!!!
they are very crazy how did you make them
men wtf… lmao
If you really want adjustable cranks couldn’t you make a set of 7" cranks, that also have pedal holes at 6", 5" etc. Then you would only have to unscrew the pedals and put them back instead of having to take off a bunch of U-bolts. But I guess those would have to be manufactured anc couldnt’ be home built.
The u-bolts are sordof necessary, if the pedal was directly in the tubing, instead of off of the u-bolt, his leg would nail the excess part of the tubing whenever it came around.
Cool project and low budget. Thanks for posting the pics.
da Vinci Designs makes an adjustable crank like that.
If you wanted to make your own you could probably start with the Kooka cranks that used to be available. The Kooka’s have enough excess material that you could drill more pedal holes in the cranks. There are probably a few other cranks have enough excess material to be able to handle a few extra pedal holes. With most cranks you wouldn’t be able to do it since there is not enough material or the shape of the crank is wrong.
“running water” engineering
This what I call “running water engineering”, in that I chose the path of least resistance, much like running water.
I didn’t have access, and was too lazy to track down, a tap for left-handed 9/16 pedals. And I don’t have a milling machine to drill the taper square holes.
So that led me to my design. Yes, it would have been better to just have more pedal holes, but this is an acceptable compromise.
In the last couple of days I have put a couple of miles on them, trying all the different lengths. They seem quite sturdy, so far. I’ll try a longer ride this weekend.
4.5" - small, really cooks along. There is alot of rotating mass but I was pleasantly surprised at how much it dampens side-to-side wheel wobbling. The long legs of the brackets don’t come that close to my legs (whew), and my footwear clears the u-bolts without touching.
5.5" - 140mm - I think this is the perfect size for my terrain.
6.5" - Good for light offroad. I was tooling around in a soccer field, no way I could have ridden that on the 4.5 setting.
7.5" - Useless. Way too much leg movement, it feels like you can’t get any torque, the geometry is strange. I’m probably going to eliminate this setting by cutting 1.5" off the end of the brackets.
In case you are wondering, I screwed up when measuring and didn’t reach my goal of 4, 5, 6" settings. And I was originally going to make it adjustable by 0.5" increments, but the u-bolts are too big and there wouldn’t be enough metal for strength.
Nice I know have a project to work on sometime in 2 years here at Williamson.
They look like they work well the only draw back to them seems to be the bolting and unbolting.