Am I missing something? Wouldn’t it be easier to just have one gear and one chain. If I could weld I would be experimenting with a set up like that.
Then it would run backwards, like a 2 wheeler. So yes, you are missing something. Before you build a design it helps to try and think through it completely, or at least to the point where you know which direction the wheel will spin.
It must either be 2 chains or 2 gears. Also, why use a gear? They are more expensive, harder to make, harder to tension, and not any more dependable than a chain.
Re: Unisk8r Geared 36"
On Fri, 3 Dec 2004 18:02:27 -0600, “oxfordrider” wrote:
>Am I missing something? Wouldn’t it be easier to just have one gear and
>one chain.
Yes you are missing something, and I think Gerble is missing something
too unless I am more confused than I know. The two chains in unisk8r’s
design operate together to make ONE gear only. One chain drives an
auxiliary axle, the second chain drives the hub.
Klaas Bil - Newsgroup Addict
“Deflating pi does not reduce calories, it just concentrates them. - billham”
You are thinking of gear in a different manner than I. By one gear I am thinking a chain on the outside and a gear on the inside. If by “one gear” it is meant that there is only 1 possible gear ration useable, then you are right, the jackshift setup is only 1 gear.
36"
I was thinking of a set up similar to a giraffe. Why wouldn’t that work?
Has anyone ever thought about using a drive belt and pulleys? Either a standard V belt or a cogged belt.
Re: 36"
It could work, except that it would BE a giraffe. You see, the cranks would need to have to be a distance above the axle in order to run a chain, and once you have them high enough to clear the wheel, well, then you have a 36" giraffe. Not that there’s anything wrong with that. I suppose there would be a sense of adventure to having your head 9’ above the ground while riding on one wheel at 17+mph.
“I suppose there would be a sense of adventure to having your head 9’ above the ground while riding on one wheel at 17+mph.”
Having ridden my 5-foot giraffe - which is geared to make it equivalent to a 37.5" wheel - at a pretty good speed, I would say there is definitely a sense of adventure… I’d love to take a 9’ high giraffe with a Coker wheel out for a spin… the adventure factor would definitely be greater… and my geared giraffe practice shopuld help out!
36"
I was thinking more of a reversed girafe, ie cranks in normal position and sprocket up higher.
There is only one “fixed gear”, in the ratio determined by the cog sizes. The jackshaft assembly simply ties the 2 upper cogs together, to transmit drive energy across and down to the hub.
See my previous posts…I already threw the idea out there of cogged belts, and that’s gonna be the drive system for my next model.
I’m slowly working out some ideas that would use a belt drive in a CV transmission. I’m basing my ideas on waveform gearing concepts.
I believe that if I can get it to work it would be the first shiftable (continuously variable no less) unicycle.
Since it’s all been in my head so far I don’t have any drawings or anything. If I ever get serious about it I’ll post what I create for feedback.
-mg
Re: Unisk8r Geared 36"
On Sat, 4 Dec 2004 21:35:22 -0600, “mgrant”
<mgrant@NoEmail.Message.Poster.at.Unicyclist.com> wrote:
>Since it’s all been in my head so far I don’t have any drawings or
>anything.
There are drawings and a description of the principle on
<http://cvt.com.sapo.pt/waveform/waveformgearing.htm>. Interesting
concept. I don’t understand how the belt stays ‘dented’ where there’s
no idler wheel. And if it doesn’t, whether it still gears as much.
Klaas Bil - Newsgroup Addict
“Deflating pi does not reduce calories, it just concentrates them. - billham”
Re: Re: Unisk8r Geared 36"
Is this for real?
If you reduce a chain drive to levers (which is what it really is for ratio numbers), the distance the chain is from the pivot points (the fulcrum) when it makes first contact with the teeth is the only place that is important for setting the ratio. The length of chain used is irrelevant. The contact point on this system essentially stays the same at all times; hence the ratio would remain the same. This system looks like it would change the distance between the drive and driven sprockets, not the ratio. The depth that a chain is on a sprocket only affects the amount of power that can be transmitted without damaging the sprocket.
And I agree with you - what keeps the belt dented where there’s no idler.
I haven’t got a clue what keeps the belt dented, but i’m sure they’ve come up with something… (probably!)
changing the length of the effective “lever” will change the size of the moment which is transmitted, but the waveform idea can still change the gear ratio.
Surely you would agree that, if we were just using a normal belt with normal pulley wheels, if there was a bigger wheel on the primary drive, the final drive would be spinning faster. This is because the wheel on the primary drive has a larger circumference(sp) so it pulls more of the belt across it each time it turns. The waveform idea effectively makes the pulley bigger, by pushing the belt into the gaps between the teeth, so when the pulley turns it pulls more of the belt through.
the problems i can see with it are:
- when in low gear, the belt is only in contact with the tips of the teeth, so i would think you would lose traction, especially if it’s wet.
- The whole system is only as strong as the mechanism that holds the idler wheel. The force of the belt trying to push that wheel away would be enormous. ands there would be a lot of friction if the bearings the idler wheel is on were not up to scratch.
Re: Re: Re: Unisk8r Geared 36"
Good question. There are very few places where Google finds this. From reading those, it seems to be an as yet untested idea (with serious intention though).
Klaas Bil
(Reposted directly to the forum because the original reply via Usenet doesn’t seem to have made it here.)
Re: Re: Unisk8r Geared 36"
The belt does not stay dented as is shown in the pictures on the website referred to above. The waveform is only applied where the idler wheel engages the drive pulley.
The more you can deform the belt the greater the changes in gearing. I envision a system with two or more idler wheels that adjust in and out to alter the gear ratio.
Since I have no access to the type of equipment needed to create such a design I’m going to start crudely and build a wooden model that should demonstrate the theory. If that goes well I’ll engage the help of a machinist to build parts that could be used for a unicycle.
-mg
If I view that Waveform drawing correctly, the axles of the blue “input” drive and the grey “final” drive remain centered in the sprockets which are mounted to them. Thus the diameter of those sprockets always remains the same, REGARDLESS of where the chain may actually contact those sprockets (which contact point is varied by the idler gear). Now I’m the one missing something, because I can’t see how changing the chain contact point on the sprocket can change the gear ratio between the input and final sprockets.
I have not seen this design prior to this thread, so I am no way an expert on the subject. And like you, I was unable to see how this design would work. That was until I took a second look at it now. I think the key is to imagine this design using a smooth belt and not a chain. With a chain, the links must mesh with teeth of the sprockets. With a belt, the belt can be in any position in relation to the sprocket. (NOTE: I know I’m not making much sense, but I’m having a load of trouble putting my thoughts into words)
The general principal is, the belt has to travel farther when the idler sprocket is engaged because follows the teeth of the input drive sprocket, and that effectively increases the diameter of the input drive. When the idler is disengaged, the belt travels a smaller distance and that results in a “smaller” input sprocket diameter.
I’m not certain I have the concept right. I haven’t had time to read through the entire article, and I’m very tired, so it’s possible I only think I know what I’m talking about.
EDIT: one part of waveform gearing I’m having a hard time understanding is why the belt stays contoured to the input sprocket after contact with the idler gear (as shown in the diagrams). Anyone know?
Re: 36"
If you did this, the higher sprocket would be connected to the cranks via a chain but disconnected from the wheel (remember, the cranks are connected to the axle which passes through the center of the hub but spin independently of it because of the bearings.
The thing that I think is odd about this design is that either the belt has to be elastic enough to stretch when the teeth are meshed further, or else the axles of the drive and output cogs have to move closer together.
The first option would be bad (certainly on a unicycle) because it would effectively create a spongy feel to the drive, and the second would involve the complication of having to slide the axles apart or together in the dropouts.