Tri star wheel on a dirt bike?

Hi all,
I was a fan of Damnation Alley back in the 70's and a year ago I saw one of these "stair climber" carts on the web.

That got me thinking. Could I do the Erzberg Rodeo with this kind of wheel? Would that give me an advantage in "Carls Diner"?

So I started designing and building last year. Now I have it finished and took it for a test ride yesterday when the MX track finally opened up near me in Berlin.

It has a major flaw so I think it has no value for a patent. I have no plans to go to Austria with it yet.

But you guys might like to see it and maybe how I built it.

I had a few limitations, some due to Covid
1. No hardware stores are open.
2. I live in an apartment
3. No garage
4. No machine tools

But I could order whatever on Amazon and other sites.

In the end I managed to get it done. Here is the final result.



Let me know If you want to see more. I already posted how I modified the wheels in the "what did you do in your garage today" thread.

But I have lots more details and videos if you are interested.

I also have the videos of me landing on my head while testing this yesterday.

I called it the NealWheel

Post up more details, it's certainly interesting!

How does it handle, it seems like with two contact patches it might handle weird?

Did you come up with a system for braking, that seems like it might be a weakness of the system?

Lastly, is it TÜV approved?

Two contact patches on the front and no front brake, how does it handle? Riding than going over rocks and steps will obviously be the strong point and I understand your theory but how will it handle in corners and general riding. Keep us updated, it is experiments like this that keep us progressing.

OK, I will post up more details soon.

I do have a few designs for the brake system and also for the back wheel with drive and brake. Its more complicated but possible.

The two contact patches fight against any turning of the handlebars. In my apartments garage, it was very difficult to move them at all. Out on the dirt it was much easier. But when you do manage to move the handlebars, its only because one wheel or the other has broken traction. If its the back wheel (of the two front ones) then it feels like the hole bike slides a little and the steering goes from resisting you to forcing you to turn harder. If its the front wheel (which isnt very often) it just goes down fast. Not much you can do to keep the bike upright. I had this problem when I was doing a turn or just correcting in a muddy spot. It was sketchy even on my normal wheels.

I took my caliper off and ziptied it to the bark busters. But first I put a screwdriver bit in between the pads and taped it up. I knew that I would try that front brake lever and I have seen the pistons come out of the calipers when the pads are worn (like mine are) and there is no disc. So squeezing the front brake made me feel better but it didn't to anything. Mostly I rode slow enough that I didn't use any brakes during the test rides.

You can see in the video that the first time I tried going over the pipe, I leaned back and gave it a bit of gas. It was much less of an impact than a normal wheel. The next time I tried just slamming into it without giving it gas. I think I would have gone over the bars with a normal wheel. Instead I felt a bang then I was over the pipe. The biggest impact was always the rear wheel.

But unless I can figure out a way to make each wheel turn independently yet still maintain the arrangement, this wheel is a non-starter as far as the market goes. No one would buy it.

I want to test it out on a big pile of rocks and boulders next.
Maybe after that I'll try the TUV

In the meantime, here is the first ride on the track with it.

It'd probably work really well with hub motors and some clever.

Segway type clever, keep it with one wheel at the bottom (mostly). All the advantages of a 15" and 25" front wheel.

Definitely interesting and there are some advantages to this system. I am wondering if a front brake, similar to a bicycle would work? While not the strongest braking, it is better than nothing. It could only be one one wheel as well, unless. . .

Or how about a electromagnet induction brake in the hubs of all three wheels. If you could make it progressively energized that could work no matter which three wheels are down, and could be very powerful.

Very interesting problem solving exercise.

I would think clearance between the top wheel and the triple clamp might be a problem, but I was also thinking, if you could get strong enough radio servos, like from an rc plane or something, and some front drum brakes, you could have an electrically actuated front brake. Anything with cables or hoses would get twisted up.

We had them here at Brize for years, are you thinking front or rear?

So far I am only working on the front wheel. I am trying to work out a solution to the steering problem. I think that is a harder problem than the brakes. (They both are not easy)

The back wheel is harder to find small enough wheels to fit it.

I was a bit worried that if I bottomed out the suspension, it would snap my front fender.

You a fan of the Tyrrel P34?



To answer your thoughts about getting steering to work properly, it makes me think about Ackermann and its relationship to steering geometry: https://en.m.wikipedia.org/wiki/Ackermann_steering_geometry

I think the issue of trying to get the wheels to (necessarily) turn at different rates, the front probably less sharply than the rear, would be the challenge to get it to handle 'well'.

I almost think too that you would have to create linkages to turn the wheels, and disconnect the movement of the forks from a linear motion with the wheels, if that makes sense, kind of like hub centric steering on some motorcycles.

Of course, that greatly complicates things further, and at that point, changing the suspension design to something other than forks starts to make more sense when trying to separate steering from suspension.

Something like this comes to mind:
https://www.odd-bike.com/2013/03/yamaha-n-d-ffe-350-forkless-two-smoker.html?m=1

Or this:
https://www.odd-bike.com/2013/03/vyrus-motorcycles-hub-centre-perfection.html?m=1

Wow,
Never seen any of these things. Thank you.

Hub steering seems like the only way its going to work. The problem comes when you want the back wheel to steer not so far as the front. In a star wheel, the wheels are constantly changing position so what was once the back wheel is later the front wheel.

I had also thought about a front swingarm design. Not as nice as it would be best if it could just replace your normal front wheel (and later the back) already on your bike.

Back to the drawing board!

I think that the geometry issues are such that it'll never be completely bolt on, particularly with reference to the clearance between the suspension and the top wheel. That being said, I look forward to seeing what you come up with!

You need to mechanically uncouple steering from the steer tube and each wheel needs its own hub steering mechanism that is independent of the tri-star rotating unit. You would need something similar to a helicopters swash plate to allow steering commands to be mechanically passed through the tri-star hub to the individual wheel hubs. And if that is not complicated enough for you, you would need some kind of four bar link connecting the swash plate to the tri-star so that you can force the front-front wheel to steer a separate arc from the rear-front wheel regardless of the rotated position of the tri-star.

https://en.m.wikipedia.org/wiki/Swashplate_(aeronautics)

I don’t think we (humans) fully understand two wheeled vehicle dynamics so throwing a third wheel in line is an amusing addition to the nightmare. You take it a step farther still by adding the rotating mechanism and a fourth.

This is a stupendously unique mechanical design problem, I would have killed for such a cool senior project in undergrad mechanical engineering and I suspect it is complicated enough to be a master’s or doctorate project. I wouldn’t know how to measure the appropriate difference in turning radius as it relates to steering input for a given lean angle let alone how to make the bike adjust automatically.

When I was a kid I tried to make something like a skateboard with only two wheels or a scooter with no handlebars. It was an unending nightmare, impossible to steer and balance. Decades later all the kids are riding on ripsticks. This problem can be solved...

how about a way to keep one wheel on the ground at a time, but it would still rotate over obstacles. A circular shock absorber in the center of the hub, with indents that snap back into position with only one wheel on the ground, but "break free" when enough force is applied.

Another thought, is the end result really much different then just having a larger DIA wheel ?

Yes, I think you are on to something there. I have already been looking at and trying to design a hub steering design. But the control is very complicated and I think an adaptation of the swash plate control might just be the key. The thing that sticks in my head though is this:

When the handlebars are turned to the left. The current front wheel should turn to the left and I think the current back wheel should turn to the Right. That should create an arc with the back wheel that will turn the bike. One problem is that what happens when that front wheel suddenly becomes the back wheel after hitting an obstacle in the middle of the turn. Now it has to also suddenly turn the other way. (that might be easy while it is the only wheel on the ground at this moment.)

So some aspects of the swash plate I could see working here.

I don't have a ME degree and I have learned Solidworks via Youtube. Glad to note I am now doing engineering on a PHD level!

I'm just a dumb old mechanic, but I suspect that the tristar wheel is best utilized for furniture dollies and hand trucks. For virtually all vehicular uses, a large wheel that circumscribes the same functional diameter would work better and be simpler, even with self-repairing anti-cockroach zombie annihilator functions.

Change my mind.

Thinking out loud here but with your front brake why not get a disc made up that bolts to the end of each "star point" something like a Buell disc that was bolted to the rim.

It would mean having the caliper a lot further away from the fork but might work. Biggest problem I can see would be the clearance between the wheel and fork or you could make a leading link which would solve that problem but then create another one with how far back the swingarm pivot point needs to be. At least with a leading link you can move the shocks and the legs further away from the wheels.

Note Greeves dirt bikes used leading links decades ago so that's not new.

As I said just thinking out loud and I am by no means an engineer

That is the purpose of this project. To find out if its better or not.

Why is it better on the hand trucks? I bet they have the same problem turning. (never tried one)

There are papers and ads for the stair climbers that all claim its better.
This for example:

https://www.researchgate.net/public...ri-star_wheel_system_for_stair_climbing_robot

So far my conclusion is that as long as you travel in a straight line, the tri-star is better at going over obstacles. Take a look at the original video in slow motion, you can see the suspension reacts way more in the rear than in the front. I also notice it reacting to small bumps in the road. Just like in the original patent:

https://en.wikipedia.org/wiki/Tri-star_(wheel_arrangement)#/media/File:TriStarAnimated.gif

I want to film it going over a section of whoops the next time. (if I can find them)

But, since all vehicles need to turn and this prototype turns like an old Buick with the wheels missing, I would say that at least this model is not better at all.


The fun is trying to come up with a wheel design that actually is better. I kinda doubt that I will have anything better in the end but im having fun trying it out.