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Old 2008-02-08, 02:12 AM   #16
unibikeling
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if anyone finds anything wrong with my plans, please tell me, because i want this thing to be flawless
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Old 2008-02-08, 03:09 AM   #17
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What exactly are these "pistons" you're showing all over your designs?

It appears you're using them in places where a spring would be more appropriate.

Keep in mind, also, that most pistons operate via the flow of a gas or fluid. This means they'll act (or react) much slower than a spring would. Also, in many cases, a spring is much lighter than a piston of comparable size.

Looking at your design, you've got pistons damping the action between the wheel and frame, and another piston tensioning the chain. What would happen if the suspension piston acted faster than the tension piston? Your chain would slip or break.

Before you start incorporating such complicated components as pistons in your design, perhaps you should first study them in isolation. What are they used for? How are they used? What limits must one consider when using the piston (such as strength)? How does one select an appropriate piston for a given application?

Springs are much simpler to understand and implement. Perhaps you should consider using springs in your first design, then add pistons once you understand the forces and reactions involved in your suspension system.
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Old 2008-02-08, 03:12 AM   #18
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Another thought...

It looks like you've got four chains in your design. You should be able to get away with three... you'll def. need one chain for each crank, but why two chains for the wheel?

Motorcycles, bicycles, and some giraffe unis all use one chain to connect the drive shaft to the wheel... why don't you?
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Old 2008-02-08, 03:19 AM   #19
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How about using a shaft instead of a chain to power the wheel. Check out Christini AWD, it seems like it would be a good option eliminating the need for the moving chain tensioner (and therefore some slop and many other problems). You would probably need to have the gears cut square instead of on an angle though so it can transfer power in both directions.

It might be easier to build a strong connection between the cranks and frame if you lowered them to just below the wheel axle. Or along side the leg of the frame if you don't want them that low.

edit, forgot to add the link

Last edited by saskatchewanian; 2008-02-08 at 03:26 AM.
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Old 2008-02-08, 03:21 AM   #20
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Im bored in my drafting class so if you can send me a clear picture with all the dimensions on it I can prolly whip it up for you on Autocad. Check out my avatar it is my torker cx drawing that I did on autocad.
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Old 2008-02-08, 03:23 AM   #21
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From the top down:

The single bearing holding the top cog shaft is going to be trouble. As you pedal you alternately apply force with your legs. This will strongly tension only one of the chains at a time. This unbalanced force will cause your long cog shaft to rock back and forth across the single bearing attached to the seat post tube. The cogs at this point are right by the bottoms of your thighs. Ouch.

I can't tell if there are two frame pistons and two tensioning pistons but I think there are. Let's replace the frame pistons with shock absorbers because that's what you're trying to do there. Each will have a spring (or compressed air chamber) and a damping mechanism of some sort to slow down its response and keep it from oscillating. It's kind of important that you get this time constant right otherwise it will be hard as a brick or mushy as Jello. This really takes a bit of thought to get right. Maybe the shocks from the vehicles you describe will work, or maybe one of the parameters will be off two orders of magnitude.

The chain tensioning pistons (and this is where you are REALLY going to run into trouble) should be replaced with VERY, VERY, VERY strong springs. You want springs here because you need fast response to keep up with the constantly and rapidly changing chain tension. A piston (compressed air chamber) or any kind of added damping will slow this component down too much. The reason this is going to give you trouble is because you're asking it to travel a large distance very quickly as you vary the chain tension from zero to HUGE.

I don't see a good anchor for your split crank assembly. It looks as if the cranks are coming off of the thin walled tubing of the frame leg on the outside of that tube only. It's difficult to see how they are to be attached but if they are only attached to the side of the frame and each crank axle has only one bearing then when you apply torque by pushing the pedal, that bearing is going to want to bind.

Sorry, that's the way I see it. I hope you keep at it because it's a cool project and concept. I would strongly recommend that you eliminate any dynamic chain tensioning scheme first.
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Old 2008-02-08, 03:40 AM   #22
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Quote:
Originally Posted by harper
From the top down:

The single bearing holding the top cog shaft is going to be trouble. As you pedal you alternately apply force with your legs. This will strongly tension only one of the chains at a time. This unbalanced force will cause your long cog shaft to rock back and forth across the single bearing attached to the seat post tube. The cogs at this point are right by the bottoms of your thighs. Ouch.

I can't tell if there are two frame pistons and two tensioning pistons but I think there are. Let's replace the frame pistons with shock absorbers because that's what you're trying to do there. Each will have a spring (or compressed air chamber) and a damping mechanism of some sort to slow down its response and keep it from oscillating. It's kind of important that you get this time constant right otherwise it will be hard as a brick or mushy as Jello. This really takes a bit of thought to get right. Maybe the shocks from the vehicles you describe will work, or maybe one of the parameters will be off two orders of magnitude.

The chain tensioning pistons (and this is where you are REALLY going to run into trouble) should be replaced with VERY, VERY, VERY strong springs. You want springs here because you need fast response to keep up with the constantly and rapidly changing chain tension. A piston (compressed air chamber) or any kind of added damping will slow this component down too much. The reason this is going to give you trouble is because you're asking it to travel a large distance very quickly as you vary the chain tension from zero to HUGE.

I don't see a good anchor for your split crank assembly. It looks as if the cranks are coming off of the thin walled tubing of the frame leg on the outside of that tube only. It's difficult to see how they are to be attached but if they are only attached to the side of the frame and each crank axle has only one bearing then when you apply torque by pushing the pedal, that bearing is going to want to bind.

Sorry, that's the way I see it. I hope you keep at it because it's a cool project and concept. I would strongly recommend that you eliminate any dynamic chain tensioning scheme first.
Yes, i know the flaws like that. Thanks for telling me about the pistons, Its just the fact that i have access to pistons and shocks from snomobeiles, Im just trying to use what i have, I think my design is actually really simple, i mean, its not perfect, but ive got time to work it out i think. And the axel on the seatpost area, thats like a last minute thing i did, when i so it im going to have a braket on it actually. And the system i did it in was fashioning it like a double chain giraffe uni, that was my main inpiration. Its just a little to try and get everything to slide liek that, im going to start building it soon, just have a few parts to get. Thanks for your responses guys Im going to end up making a few more drafts of this, i'll get some dimensions up and stuff. Its practically a short giraffe unicycle. Some of the things in it are simply genious from my brother and dad, like the berrings are going to be held with berring housings, like the enclosures on frames. It's still experimental

Edit: Im going to probably make some enclosure for the whole setup also, That sketch is really poorly drawn, its not to scale totaly. Its gonna take some time still to work the kinks out. Im going to try and make everything as small as i can. My 1:1 gear racio is like it is because i dont feel like fiddling with things. I'll sketch more up, taking 2 hours a drawing, it might take me some more time
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Last edited by unibikeling; 2008-02-08 at 03:43 AM.
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Old 2008-02-08, 03:43 AM   #23
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Quote:
Originally Posted by saskatchewanian
How about using a shaft instead of a chain to power the wheel. Check out Christini AWD, it seems like it would be a good option eliminating the need for the moving chain tensioner (and therefore some slop and many other problems). You would probably need to have the gears cut square instead of on an angle though so it can transfer power in both directions.

It might be easier to build a strong connection between the cranks and frame if you lowered them to just below the wheel axle. Or along side the leg of the frame if you don't want them that low.

edit, forgot to add the link
Overall the concept looks workable except the chain system which looks problematic.saskatchewanian's suggestions looks to be a good idea to get around the chain problem.No doubt there are still many details for you to work out but if you get the fundamentals right all the other fiddly bits can be worked out in time.Keep at it.
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Old 2008-02-08, 03:46 AM   #24
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Ok guys also, I'm like flat broke, so im not spending money on it lol.... I'm scavanging parts from my grandpas huge junk pile, and a metal shop thats free for me to use, minus metals from there. thanks for your help though guys
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Old 2008-02-08, 03:55 AM   #25
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and also, Isnt the whole point of what i drew to have the tire free traveling? Minus some small flaws in it, initially, replacing some things with springs, and supporting other things, ive created somethign that can move the tire without moving the pedals, duh! lol

Edit: When i do this, im going to re-inforce my pedal frame and stuff. I might weld more metal on it or something, to keep it stiff. Also, when i do this, im going to need to figure out how to tig weld things to the berrings, but eh, i think its going to work out all fine
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Old 2008-02-08, 04:01 AM   #26
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I don't think that the shaft drive would be all that expensive. A telescoping shaft might be a bit harder to find for cheep but it should not be hard to find cheep bevel gears. If worst comes to worst you could use two different sizes of square tubing for the shaft but then you would need to get creative with attaching bearings etc.

I will be interested in seeing what you end up building.

edit:
Quote:
Originally Posted by unibikeling
ive created somethign that can move the tire without moving the pedals, duh! lol
Not quite. When the shocks are compressed your chain tensioner is going to lengthen one side of your chain while shortening the other. If your tensioner is on the front of the frame this will turn your wheel backwards, or if the tensioner is on the back it would spin the wheel forward. And vice-versa for the cranks.

Last edited by saskatchewanian; 2008-02-08 at 04:09 AM.
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Old 2008-02-08, 04:17 AM   #27
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Quote:
Originally Posted by unibikeling
and also, Isnt the whole point of what i drew to have the tire free traveling? Minus some small flaws in it, initially, replacing some things with springs, and supporting other things, ive created somethign that can move the tire without moving the pedals, duh!
As for unicycle shock absorption for trials, I have always been a fan of adding a spring steel leaf spring to the cranks. Simple and straight-forward to implement and mechanically isolates the pedals from the unicycle.

Cut out a section of each crank between the axle and the pedal. Slot the two sides to accept some thick spring steel sheet. Perpendicular to the slots, drill holes through to accept an appropriate tap. On one side of the slot, expand the holes to clearance. Tap the holes. Insert the spring steel sheet between the two crank sections. Insert and tighten the screws to clamp the spring steel in place.
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Old 2008-02-08, 04:23 AM   #28
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Or maybe you could develop a hybrid unicycle/pogo stick for really big hops...
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Old 2008-02-08, 04:41 AM   #29
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Quote:
Originally Posted by harper
As for unicycle shock absorption for trials, I have always been a fan of adding a spring steel leaf spring to the cranks.

Thus:
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Old 2008-02-08, 04:46 AM   #30
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That's a really good Idea, I wonder why it's never been discussed before. Or maybe it has....
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