I’ve come up with an idea for a crank set that might be worth while. I’ve created a nested album with my prototype frame pictures and posted photos and text there.
The key component is a device called a “keyless hub”. It’s pretty cool … when screws are tightened the outside expands while the inside shrinks therefore locking whatever is housing it to a shaft … crank arms in this case. Here’s a link for more information on the thing:
In theory the cranks won’t slip on the shaft up to a total load on the pedals of about 800 pounds. Note that there are no splines, keys etc. It just grabs the shaft and holds on!
The axle is made from 17-4ph stainless steel that’s heat treatable and nearly as strong as chromolly. The hub flanges are 304 stainless steel welded right on to the axle then the whole thing heat treated.
The cranks are 6061 aluminum. 6061 normally wouldn’t be strong enough for crank arms but these are so wide that they should be ok.
Total unit weight (without the bearings) is 3 pounds. Can’t wait to get it built up with a rim for a test ride …
You are, like, WAY out on the edge (the CNC edge, anyway). If you keep producing such impressive work, we’ll end up becoming desensitized. “Hey, you see what Steve did today?”
Thanks for the link to the manufacturer of the Keyless Connection- it will be interesting to see how they hold up. What does a connector cost, BTW? I presume they are inexpensive enough to make this more than an achedemic persuit.
How has the frame been performing? Was twist a problem, after all? Have the cold connections proved durrable?
What are you doing reading posts? Build that wheel, get out there and RIDE.
I’m kind of a newbie on the CNC mill. We’ve had it for a couple of years but I haven’t personally done anything with it until recently. It’s an adrenaline rush when you press the “go” button on the first run of a new program … the mill is so unforgiving and powerful that a small programming error can cause lots of flying metal!
The keyless hubs cost about $32 each from McMaster Carr but I’m sure they can purchased in quantity from a distributor for less than that. The axle cost about $5 and eveything else I scrounged.
So far so good with the new frame. I haven’t been riding a lot though because it’s just been so stinkin’ cold.
Forgive me, but what is the advantage to this over regular cranks and a hub? It is neat looking, but I dont see how this solves a problem.
-David Kaplan
You do such elegant work, Steve. Is 800 lbs the force that can be applied to the pedal for the break-torque condition on the clamp or is that at the yield limit of the aluminum crank? At what drop height do you think an 800 lb impulse might occur? Your flange welds are beautiful. The CNC work is artistic.
Once durability is established, it could potentialy provide alternitaves to the Profile hub. With traditional hubs, the failure point is usualy at the hub taper seam- that would be eliminated here. Oh coarse, other special problems may be introduced. In time we will see what (if any) advantage is garnered. If crank slipage only occured in cercomstances that would normaly result in part failure, it may be a boon for crank/axel longevity.
It also allows Steve to bask in the glory of creation- which I’m all for. Go STEVE, GO STEVE!
Chris pretty much sums it up. The cost of the keyless hub might be offset by ease of fabrication and less machine work. I think it would be relatively inexpensive to make a titanium axle, for instance, since there would be very little machine work needed.
Chris’s observation that the hub might slip before something breaks is a “feature” I didn’t think about … an overload clutch!
Another advantage of this design is there should be NO creaking coming from the crank/axle interface.
As for the loading on the cranks and axle …
The specs for the keyless hub states a “maximum transmittable torque” of 229 foot pounds. My cranks are 170 mm (.56 feet) long so (229/.56) = 409 pounds per crank or about 800 pounds total for both cranks. How much load is applied by a drop of some distance is a tough question … so many variables such as tire pressure, rim flex, crank flex, axle flex, technique etc.
I read somewhere that David Mariner (sp?) has a strain gauge setup that he’s been using to record loads on a unicycle at various points and has recorded up to four times the rider’s body weight on the pedals. It wasn’t stated under what circumstance he saw that kind load though.
Looks excellent, if you can work out bugs it could revolutionise cranks on unicycles and bikes, as there are always problems with them!
How did you make sure the cranks are tightened level? by eye or actually with a level, and supposing the cranks swiveled on a particually hard drop, how could you level it out on the trail. Just a thought. mabey some markings on the end of the axle to line up with markings on the crank?
Looks damn good, and simple, but sometimes the simplist things work best! Keep at it, ill buy one if you get it to work!
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Steve,
How much is the final cost? Have you weighed the hub w/ cranks? That is
an amazing unit!
Jeff Tuttle
On Mon, 4 Feb 2002 19:46:43 +0000 (UTC) showard
<forum.member@unicyclist.com> writes: > Chris - > > I’m kind of a newbie on the CNC mill. We’ve had it for a > couple of years but I haven’t personally done anything with it > until > recently. It’s an adrenaline rush when you press the “go” button > on > the first run of a new program … the mill is so unforgiving and > powerful that a small programming error can cause lots of flying > metal! > > The keyless hubs cost about $32 each from McMaster Carr but > I’m sure they can purchased in quantity from a distributor for less > than that. The axle cost about $5 and eveything else I scrounged. > So far so good with the new frame. I haven’t been riding a lot > though > because it’s just been so stinkin’ cold. > > Steve Howard > > > > > – > showard > Posted via the Unicyclist Community - http://unicyclist.com/forums >
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<DIV>Steve,</DIV>
<DIV>How much is the final cost? Have you weighed the hub w/ cranks? That =
is an=20
amazing unit!</DIV>
<DIV> </DIV>
<DIV>Jeff Tuttle</DIV>
<DIV> </DIV>
<DIV>On Mon, 4 Feb 2002 19:46:43 +0000 (UTC) showard <<A=20
href=3D"mailto:forum.member@unicyclist.com">forum.member@unicyclist.com</A>=
>=20
writes:<BR>> Chris -<BR>> <BR>> I’m kind of a newbie on the CNC=20
mill. We’ve had it for a<BR>> couple of years but I haven’t =
personally=20
done anything with it <BR>> until<BR>> recently. It’s an =
adrenaline=20
rush when you press the “go” button <BR>> on<BR>> the first run of a =
new=20
program … the mill is so unforgiving and<BR>> powerful that a small=20
programming error can cause lots of flying<BR>> metal!<BR>> <BR>> =
The=20
keyless hubs cost about $32 each from McMaster Carr but<BR>> I’m sure =
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can purchased in quantity from a distributor for less<BR>> than that.&=
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The axle cost about $5 and eveything else I scrounged.<BR>> So far so =
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<BR>> <BR>> <BR>> <BR>> --<BR>> showard<BR>> Posted via =
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I have about $55 in parts for this crank set. The aluminum for the crank arms was salvaged and the bearings were left over from another project (non uni related). Of course this doesn’t include any labor. The complete unit with bearings weighs about 3 1/4 pounds.
I decided that a test fixture was in order so I’ve cobbled up a “crank tester”. A picture has been added to the gallery at:
The crank set sits on a little base that supports the bearings while air cylinders push down on the pedals. The idea is to simulate “hopping”. I’m cycling the air cylinders about 85 times/minute and each cylinder pushes with a force of 250 pounds so the the cranks are seeing a 500 pound load about 3 times per second. You can see a video (kind of poor) at:
The results were pretty unremarkable. I cycled the thing 10,000 times with no failure! As a comparison I also cycled another crank set … the hub from with my Semcycle XL with 170mm bike cranks. After 7000 cycles nothing happened to it either.
What did I learn from this? Not much. I was surprised how much the axle flexes and the arms twist but without something breaking there’s not much to learn. 250 pounds force is all I can get out of the air cylinders that I’m using so I suppose I need to find some larger cylinders and try again.
Neat video. You not only do beautiful work you also do thorough testing. It looks like one cylinder drives one crank and the other one just reacts. Maybe it’s too far away to see clearly.
Why use bigger cylinders? Just use cheaters on the cranks.
The crank set looks great! I especially like the fact that the axle has a
straight and simple profile that allows trying out different materials.
How about S7 tool steel? It is very tough and is easily heat treated. The
best I’ve ever seen is CPM9V, except it is expensive to properly heat treat.
If I could offer up: http://www.sensorprod.com/pressurex.html This material
might be of some use in finding some of the loads that we all wonder about.
You might do a drop on to it or somehow get it on the pedals for finding the
forces there.
BTW, I’ve drawn up another crazy frame if anyone’s interested. I called it
a Cossack frame for those who wheel walk. My main objective was to try to
get some flex into a standard seatpost. No, I won’t be making it very soon,
but I will be trying to figure out how to get a high offset seatpost
(installed backwards) on my uni to put some spring in it. http://home.mmcable.com/masseyhp/doug/page1.html
Doug
“showard” <forum.member@unicyclist.com> wrote in message news:a3sged$600$1@laurel.tc.umn.edu… > I have about $55 in parts for this crank set. The aluminum for the > crank arms was salvaged and the bearings were left over from another > project (non uni related). Of course this doesn’t include any labor. > The complete unit with bearings weighs about 3 1/4 pounds. > > I > decided that a test fixture was in order so I’ve cobbled up a "crank > tester". A picture has been added to the gallery at: > http://www.unicyclist.com/gallery/album14 > > The crank set sits on a > little base that supports the bearings while air cylinders push down > on the pedals. The idea is to simulate “hopping”. I’m cycling the > air cylinders about 85 times/minute and each cylinder pushes with a > force of 250 pounds so the the cranks are seeing a 500 pound load > about 3 times per second. You can see a video (kind of poor) at: > http://www.atec.cc/cranktest.mpg > > The results were pretty > unremarkable. I cycled the thing 10,000 times with no failure! As a > comparison I also cycled another crank set … the hub from with my > Semcycle XL with 170mm bike cranks. After 7000 cycles nothing > happened to it either. > > What did I learn from this? Not much. I > was surprised how much the axle flexes and the arms twist but without > something breaking there’s not much to learn. 250 pounds force is all > I can get out of the air cylinders that I’m using so I suppose I need > to find some larger cylinders and try again. > > Steve Howard > > > > > – > showard > Posted via the Unicyclist Community - http://unicyclist.com/forums
The crank arms didn’t stand up well to hopping. They twisted so the pedals now point down hill. I continued hopping until one arm developed a crack in it but the keyless hubs didn’t slip. Back to the drawing board I guess.
About the latest frame:
I’ve not been able to keep 22.2 mm seat posts from twisting so the newest frame is made to fit a 27.2 mm seat post. The others have had chromolly seat tubes (except #1) but this one is aluminum. I don’t think I’ll make another frame that won’t fit a 27.2 mm seat post.
The finish is “hard coat” anodizing. This is different than the usual “ornamental” anodizing in that the surface is much harder and will stand quit a bit of abuse. However - colors end up weird since hard coat naturally has a green tint to it. I asked for red and ended up with plum. A good thing about anodizing is that it doesn’t add any weight so this frame ended up weighing less than two pounds.
I’v done a bit of anodizing of Aluminium. What is different in “hard coat”? Is the oxide layer more robust before sealing, or do they add some agent to the dye that bounds with the oxide (and thus the green tint)?
The ‘regular’ anodizing process is very low-tech- you could easly do it in house- if you have a mind to lower production costs.
BTW: I find the plum colour much more appealing than red. Happy accident, there. Martha Stewart would approve.