Another crazy contraption - suspension (not seatpost) unicycle...

I’ve always wondered what it’d be like to ride a unicycle that has proper suspension. By this I mean that you could absorb the shocks while not sitting down. So I’ve started figuring out how it’ll work and it does seem possible. Just imagine riding one of these!

There are two main styles but the shorter one would require two shocks as far as I can see and seems more complicated, so I’ll just talk about my main one for now.

The way it’ll hopefully work, is that there’ll be a chain involved and the pedals would have to be above the wheel. So it’ll probably end up being about 4’ high like a semi-giraffe or something.

At first I thought that what the chain is doing is impossible (changing from onw side of the frame to the other) but then I remembered that just above the wheel the frame goes into one tube.

The only faults I can see at the moment are:

  1. There’d probably be a fair bit of play in the chain.
  2. It’d be impossible to hop on the spot without having the pedals move in position because the suspension doesn’t go straight up and down but in a little arc.

What do you think? Please point out any errors with it.

I’m still going to have the seated hand-driven unicycle built. Hopefully before UniNats.

Thanks,
Andrew

Very creative and imaginative, and an excellent diagram.

You knew there would be a ‘but’, didn’t you?:wink:

But…


Firstly, can I put some labels on your diagram?:

From the wheel hub up to the bottom chain ring I shall call the fork

From the bottom chain ring, diagonally forwards to the second chain ring I shall call the supension mounting.

From that chain ring to the top chain ring (cranks and pedals) I shall call the swinging arm.

From there upwards I shall call the seat post.

And the spring and piston arrangement I shall call the shock absorber.


Now, is the seat post fixed in relation to the swinging arm? By this, I mean is there a solid welded join so that the swinging arm and seat post are a single component?

If YES, then as the swinging arm swings up and down with the suspension movement, the angle of the seat post will change. Every time the suspension compresses, the seat will lean backwards slightly. Every time the suspension stretches, the seat will lean forwards slightly. Disconcerting!

If NO, then you need some complex linkage (possibly some sort of pantograph) to keep the seat post vertical at all times. This will add weight and complexity.

NOW, look what happens when the swinging arm swings up and down. To visualise this easily, consider 2 extremes. At one extreme, the swinging arm could move up towards vertical; at the other, it could move down towards (or past) horizontal. Now, I KNOW that your plan is for only a few inches of movement, but stick with me for a moment…

When the swinging arm is vertical, the bottom of the seat post is well forward of the forks; when the swinging arm is horizontal, the bottom of the seat post is slightly behind the forks. With your design, allowing for maybe 4 inches of play in the suspension, the seat post would move from an inch or two forward of forks to maybe a fraction of an inch behind.

Now, what’s connecting the bottom of the seat post to the top of the forks? The shock absorber, which has a sort of piston arrangement. This would not allow the forward backward movement described above, even if the rider could cope with it.

You could address this problem several ways. You could eliminate the forward backward movement by putting a hinge where the fork meets the suspension mounting. However, you would be relying on the strength of the shock absorber to keep the whole thing in line, and the shock absorber is not designed for lateral strength.

So perhaps you could have TWO suspension mountings and two swinging arms, one pointing forwards, and one pointing backwards. These would balance each other out and the shock absorber would then only have to deal with the up and down movement. Except you have now introduced more weight and more moving parts.

And where is that weight? Some of it is below the springs, so it is ‘unsprung weight’, which is generally a Bad Thing.

So to make your idea work, you need to ‘mirror image’ the suspension arrangements (although you should get away with only one transmission train (set of chains and rings)) and you need to introduce some sort of pantograph arrangement to maintain the seat in its vertical orientation at all suspension positions.

And that makes a heavy, complex and vulnerable unicycle, all for maybe 3 or 4 inches of suspension play.

I was reminded of the problems experienced by the early steam engineers. Do you know what a beam engine looks like? It has a huge fixed piston which is connected to one end of a beam which rocks like a seesaw/teeter totter. The other end of the beam is connected to a piston too, but that piston doesn’t produce power, it is a pump. They used beam engines for pumping water up out of mines.

The problem they had was very similar: as the beam rocked, the connecting rod from the piston to the end of the beam was forced out of line. They dealt with this by quite an elegant pantograph arrangement. It’s a long time since I looked this up, so I’m rusty on the details, but I bet if you search Google for Trescothick, beam engine, and pantograph, you will find something. No doubt Mr. Harper or some of our other engineering experts in the forum will be able to direct you better.

Anyway, not to be downhearted… if you don’t think about new ideas, you don’t make progress, and if your ideas don’t work, you’ve still learned something. Keep at it, but don’t sell the bicycle shop just yet, Orville… :wink:

Mike,

Thanks a lot for all the advice. The problems with the design are exactly what I’m looking for. Now…

Now, is the seat post fixed in relation to the swinging arm? By this, I mean is there a solid welded join so that the swinging arm and seat post are a single component?
At the moment yes, keeping in mind that this is the first simple little sketch. I did think of this but hadn’t been able to come up with any solution. I guess I was just planning on ignoring it and hoping it wasn’t too disconcerting. On the other hand, I could always make it a freely swinging ‘seat post’ :). That’d be great!

Now, what’s connecting the bottom of the seat post to the top of the forks? The shock absorber, which has a sort of piston arrangement. This would not allow the forward backward movement described above, even if the rider could cope with it.
The idea was for that shock absorber to be set up as if it was on a bike. Where it connects to the swing arm and suspension mounting, it would be ‘hinged’. Keeping this in mind, would that still be a problem?

So perhaps you could have TWO suspension mountings and two swinging arms, one pointing forwards, and one pointing backwards. These would balance each other out and the shock absorber would then only have to deal with the up and down movement. Except you have now introduced more weight and more moving parts.
I like that idea. I’m not really worried too much about weight because this is just going to be a fun little thing to bob around on, but I’m having trouble picturing a simple enough linkage. The problem I keep coming across is that I look at my little design and start thinking in 2D. In 3D it becomes much more complex.

And where is that weight? Some of it is below the springs, so it is ‘unsprung weight’, which is generally a Bad Thing.
Could you please explain (briefly) why?

So to make your idea work, you need to ‘mirror image’ the suspension arrangements (although you should get away with only one transmission train (set of chains and rings)) and you need to introduce some sort of pantograph arrangement to maintain the seat in its vertical orientation at all suspension positions.
This is an idea I had about 2 minutes ago so I haven’t thought it out much, but couldn’t you set up one shock absorber on the front and one on the back connecting the swing arm to the seat post? That way, if you ease off the ‘strength’ (I couldn’t think of a more appropriate word) of the main shock absorber, you could keep the seat post upright while avoiding complex linkages and so on. Please feel free to pick this idea apart…it’s just a thought.

Thanks a lot for your help. You must have spent a fairly long time on that and I do appreciate it.

Any other suggestions from other people are more than welcome.

Thanks,
Andrew

I think its already been done, but why not just use something similar to a bike suspension fork as a frame? as long as it has the clearance and enough stiffness to take your full weight. Wouldnt that be much simpler to build

I think Andrew is (correct me if I’m wrong) attempting to design a unicycle in which the suspension is below the pedals, allowing an interesting dimension to hop on/pedal on…

One little thing, Andrew (and I aint no physicist/engineer/metalworker/expert, I’m a humble law student) can you imagine pedaling it uphill? Would the shocks (Help me maths type/physics type people) absorb some of the power, as per those dual shock downhill mtb’s you see going up hill where the shocks absorb a lot of the power?

I think it’s a great idea!

Go for it, you have out support.
I think the pantograph idea for the seat post is a good one. I don’t think the extra weight would be all that bad, and having the seat constantly in the same angle is worth the extra weight.

I think one of the biggest problems with the design is the height of the cycle. I believe that the design can be made to work, with a few adjustments, but the added height would greatly reduce the practicality of it.

Keeping the height thing in mind, I threw together the following picture. I think it addresses the height issue, but produces a whole slew of other problems. Keep in mind that just about everything on this cycle is hinged.

Daniel

uni.jpg

Exactly. Hopefully it’ll feel really strange to ride.

I’m sure they probably would but this isn’t for any really long distance riding or anything like that. It’s just a fun little project. I guess I could always design some sort of anti-bobbing system like on higher end duallies. :slight_smile:
Daniel,

I like that modification and I’d also prefer not to have the extra height. I’m still not sure what I’ll do to keep the seat upright. Just one question - did you mean for the frame to join into one tube in the spots where I’ve marked? I think it’d be a lot simpler this way. Also, what ‘whole slew of other problems’ are you refering to? Thanks a lot for posting that suggestion, I like it.

I guess a 20" wheel would be best for this because it’d reduce the height a lot. Any thoughts?

Please keep the suggestions coming,
Andrew

p.s. I guess another question I have to face is will I bild this or the seated hand-driven one first?

attachment.jpg

When I made the drawing, I was thinking only in 2-d. I didn’t out any thought into weather it would be one or two pipes. I was just kinda messing around.

I would think that this cycle would be good for long distance riding. I mean it doesn’t really fit in any other category; you can’t do any trials on it, freestyle… uh NO!, I don’t think you would want to use it for MUni because of all the parts that would get damaged during falls, the only things left are XC and distance.

The whole slew of other problems I am talking about is referring mainly to the transition from 2d to 3d. What looks good on paper might be down right impossible in real life.

On a side note, I think you might be able to get some very hops with it. From what I can see, it would act a pogo stick with a wheel.

Daniel

Andrew. I love that design and I think it’s going on my Desktop as a nice wallpaper. I got the Hyder Twins Sisters on my Computer screen at the moment riding a Giraffe unicycles. Sorry Girls you’re going. Good luck with that project Andrew and keep us up to date with it. I love to try it out one day with a similar design like that.
And Samuel, good luck with the law Studies. I’m now doing Computer Building right now as we speak. I’m took up Paper delivering too.

David.

i dont want to ride a placinta…slim it down.

Well I guess so, but I thought it’d just fit into the category of suspension unicycling. It’d be fun to just ride around and bounce up and down on. If it’s strong enough, I’ll try out some high and long jumping on it.

Good to hear David, congratulations.


I’ve drawn up a rough second design. The main problems are that I still need a way to keep the seat post upright, and I’m still not thinking in 3D properly. Anyway, here it is…

I have seen a picture of a pivot suspension giraffe that reminded me of this design. I’ll see if I can find it again.

Daniel’s version would nearly work. It would still need some positive method of keeping the seat post vertical. That could be done with a pantograph arrangement, or with a simple telescopic connection from the bottom of the seat tube to the top of the fork.

If you’re going to put the shock absorbers there (not a bad idea) then you could save weight and cost by using simple ‘trapped rubber ball’ shock absorbers similar to the rear suspension on a Moulton bicycle.

What happens to all those projecting bits when you UPD? Some sort of guard would be easy to fashion, but that’s more weight and bulk

Back to basics: there are exactly three places you can put some sort of suspension on a unicycle:

  1. Between the seat and the cranks. Typical example, a telescopic spring loaded seat post. (N.B. For completeness, I’d put a sprung saddle or air saddle in this category.) This is the simplest place to put the suspension. The obvious disadvantage is that the distance between the rider’s rump and the rider’s feet varies with suspension movement - so the rider is sometimes riding with bent legs, sometimes with straight legs. This is not efficient of comfortable. The more suspension there is, the bigger the problem with variable leg extension.

  2. Between the cranks and the wheel hub. This is the idea which started this thread. This makes chain drive necessary. It introduces substantial moving parts, extra weight and complexity, and makes the unicycle vulnerable to damage in a UPD. There are problems with chain lash (in some designs) and problems maintaining the seat and forks in proper orientation. As Daniel has (nearly) shown, the idea can work in theory. Isit worth it in practice? I think the disadvantages would outweigh the advantages.

  3. Between the wheel hub and the ground. This has the advantage of keeping unsprung weight to a minimum. Two ways of doing it: a sprung hub, as used on some early motorcycles; a big fat soft tyre. A sprung hub has a conventional axle, connected to a large concentric outer hub by springs. Yuk!

For a unicycle, the simple practical answer to suspension has to be a big fat soft tyre, a sprung or air saddle, and possibly a shock absorbing seat post with a small amount of movement. Nothing complex here, and nothing which fundamentally changes the look or shape of the unicycle. You get a little bit of extra weight, a little bit of extra rolling resistance, and a small amout of variable leg extension.

Unsprung weight: Andrew asked for clarification. What happens when suspension compresses or extends is that everything below the suspension moves up and down following the contours of the ground, and everything above the suspension tends to carry on as near to level as possible. Let me illustrate with a theoretical perfect suspension on a car on a flat road. There is a speed hump. The wheels ride up and over the speed hump, and the chassis and body of the car don’t deviate at all. the driver doesn’t even feel the bump.

Now when those wheels ride up and then down the speed bump, they are using up energy. It will slow the car down, or the driver will need to put more power in to compensate.

If the wheels were twice as heavy, they would use twice as much energy to be lifted over the bump. (Yes, they would get some of the energy back as they dropped down the other side of the bump - but not all as some would be lost in heat and sound from the impact and the compression of the tyre and suspension.)

Now if the same car had no suspension at all, the whole weight of the car would be lifted by the height of the speed hump. Obviously, that would take a lot more energy - as well as being a lot less comfortable.

Here’s a true story, much simplified, and from memory, so I can’t be sure about the dates.

In about the 1960s, Alex Moulton designed the Moulton small wheel bicycle. The seat, cranks, and handle bars were in the same position relative to each other as on a conventional bicycle. However, the Moulton bicycle had very small wheels. This made the bicycle lighter, more compact, and quicker steering. But the small wheels gave it a harsher ride. They felt every bump. (Compare a Coker and a 20 inch uni!)

So Alex Moulton (now Sir Alex) invented a simple and very elegant suspension for the bicycle. The rear forks were a sort of swinging arm arrangement, and the spring was a trapped rubber ball. (Similar idea now used on the Brompton folding bicycle, I think, but I’m not sure.)

Amazing machine. Light, compact, fast, comfortable… expensive, complex…

And Raleigh, who were a major manufacturer at the time, brought out a series of bicycles called RSW - that’s Raleigh Small Wheel. They made (from memory) RSW12, RSW14 and RSW16, the number denoting the wheel size in inches.

And Raleigh, being a major company with all the resources and expertise they could desire, didn’t make fance suspension units. Oh no! They made rigid frames and used huge fat squidgy tyres. They sold by million. The Moulton died out. The neat engineering solution could not compete with the simple no nonsense approach. Why pay 3 times as much for something 10% better?

Later, Sir Alex Moulton decided to revive his idea, but this time he aimed for the connoisseurs’ market. His new cycles had a revolutionary ‘space frame’ design. They were hugely complex and expensive, but enthusiasts were determined to convince themselves that the new Moultons were in some way better than conventional bicycles. (I love the idea, but I cannot see that an expensive small wheeler with suspension has any obvious advantages over a cheaper big wheeler, apart from style and exclusivity.)

Still, Sir Alex had cornered the market. Until someone invented the fashion statement mountain bike. Because we all know that for every 500 mountain bikes sold, only 1 or 2 ever go further than 5 miles from the rider’s home. Yet almost every mountain bike on sale today has suspension front and rear, as well as disc brakes and all sorts of unnecessary fripperies. (Unnecessary for the school run, shopping, and Sunday ride on the park; useful for proper mountain biking, of course.)

So Sir Alex has lost his exclusivity, and his idea of suspension, conceived as an elegant engineering solution to a perceived problem (the “need” for a small wheeled bike) has become no more than a mainstream fashion item on fat tyred 24 geared mountain bikes used by riders who seldom go off the tarmac.

And Andrew and Daniel’s idea for this suspension unicycle fall into a similar category. There is a perceived problem - the need for suspension - and there is a reasonably elegant (but expensive and complex) solution. The simple answer (fat tyres and a bouncy seat) would do the job just as well at a fraction of the cost.

That doesn’t devalue the effort and invention that Andrew and Daniel have put in. It’s only by chasing ideas to their conclusion that we get insights at all.

Reminds me of a Swing Bike that I still got. The back wheel spins as you ride along and can do sort of tricks with it. Ride up on gutters, around the Cones all sorts of things. And that design is interesting. Well done Andrew again. And Um…Thaks for the kind words, you just cheer me up. I need that. I was down in the dumps this morning. Thanks.

David.

Yet almost every mountain bike on sale today has suspension front and rear, as well as disc brakes and all sorts of unnecessary fripperies.
Hmmm…that’s a pretty bold statement! :slight_smile:

As Daniel has (nearly) shown, the idea can work in theory. Isit worth it in practice? I think the disadvantages would outweigh the advantages.
I think it’d be a really strange and good feeling to be able to bounce along on one of these things. If there’s enough travel in it, I reckon it’d be great.

Unsprung weight: Andrew asked for clarification. What happens when suspension compresses or extends is that everything below the suspension moves up and down following the contours of the ground, and everything above the suspension tends to carry on as near to level as possible. Let me illustrate with a theoretical perfect suspension on a car on a flat road. There is a speed hump. The wheels ride up and over the speed hump, and the chassis and body of the car don’t deviate at all. the driver doesn’t even feel the bump.
Thanks.

Just on a general note, if I ever end up getting one of these made it would just be a little toy to play around on. It’s not really meant to be all that efficient or anything…it’s just a bit of fun. Just imagine bobbing around on a suspension unicycle with 6" of travel!

Thanks a lot for all the help,
Andrew

Yes, please do! I’d love to see a picture of it.

Andrew and co.
To keep the seat upright, you could drop two pieces of pipe or other lightweight material from the base of the frame to the hub…at the hub, have a hole for the metal pole to stick through and slide through (Obviously this would need to be out from the axle. The metal would only need to be like 5mm in diameter or something and be able to slide freely as the suspension moves up and down.
I would draw a diagram but am not at home (using a hospital pc) so cant edit any of your diagrams…

Something else to consider with these hinged designs. When the suspension compresses and uncompresses it’s going to cause some movement of the wheel similar to a little idle. Consider the cranks being held perfectly horizontal as if you were hopping. Now compress the suspension. The chainring at the pivot point is going to have to rotate at little bit which is going to cause the wheel to rotate a little bit. That kind of suspension induced wheel rotation could make riding the thing difficult.

These forces will also cause the suspension to either compress or decompress with heavy forcefull pedaling. So when you are pedaling hard the suspension is going to be reacting to the pedaling forces rather than reacting to bumps on the trail. That’s not what you want in a suspension design. Some poorly designed bike suspensions also suffer from heavy pedaling or breaking forces locking out the suspension.

Unidak posted this awhile ago…

Leo White

runtuni1[1].jpg

awh yes,more testament that most idea’s have already been thunk before. :slight_smile: