Mountain Bike Reviews Forum banner
1 - 20 of 22 Posts

·
Registered
Joined
·
8 Posts
Discussion Starter · #1 ·
Just helped build this recumbent - I'm not a recumbent kinda guy, but this one was fun/torturous to design and build. Rides well though!


Tig welded, mix of 4130 and bike tubing, carbon and heat-moldable-foam seat. 32 lb as it stands in the picture.
 

Attachments

·
Registered
Joined
·
399 Posts
Way interesting. Two questions. When you steer, are you pushing one handle forward, and pulling the other handle rearward (i.e. is each handle on a seperate pivot tied each handle tied to an independent tie rod, steering bar axis = left/right) or is that a solid U bar that pivots with a single tie rod, push forward to go right, pull back to go left?

How did you figure out the angle for the rear headset (oops.. tailset) tube? I'm sure that matters, but its not something that is intuitive. Is there a calculation / prediction model for stability similiar to trail?

It is a way cool project. Nice work.

zip.
 

·
lidless ascender
Joined
·
812 Posts
Looks interesting :thumbsup:
One question though: why no brake in the back?I'd feel somewhat insecure going into a slick downhill turn with only a front brake.

Marko
 

·
directionless white male
Joined
·
69 Posts
shandcycles said:
rear steer? front wheel drive? come on admit it, you just put the seat on backwards!
I haven't seen too many bents that put pedals out of the way of the cyclist so no, it isn't a matter of reversing the seat.

I like it. It's cleaner and more simple in design. I imagine weight is evenly distributed between wheels but a rider would get enough traction with the front. Ideally this design may not be right for all road types, unless it turns more quickly than I imagine. But at least if you have a mechanical problem you're not blind to it untill you stop and ruin your flow.
 

·
Registered
Joined
·
399 Posts
ref: http://en.wikipedia.org/wiki/Bicycle_and_motorcycle_dynamics Mid steering makes sense. Look at the angle of the rear fork tube.. the weight of the rider would tend to 'pull' the bike towards straight. When you turn, I imagine the rider would find himself lifting up away from the ground, similiar to how a door with a canted hinge will center to a low spot when released.

Of course you could check it via the eigenvalue calculations. :')
 

·
Registered
Joined
·
8 Posts
Discussion Starter · #14 ·
Good work engineers, zipzit's right - the weight centers the rear wheel - not as self-stabilizing as the normal bikes tendency to lean away from a steer and then steer into the lean to self correct, but it does the job.

If you look under the same youtube poster:

http://www.youtube.com/user/moynihanigan

you can find a video labeled with prototype - we built a proof-of-concept frankenstein's monster to see if it would work, then a prototype to find out what angle's, wheel positions, and seat positions worked, then built this race bike.

We haven't high speed tested the race bike as much - but the prototype has been up to 35 or so and it seems to behave intuitively - mistakes made at that speed are entirely correctable, as we came to learn from some harrowing experiences.

Push the left steering arm forward, rear wheel turns out behind you to your right which would be a turn to the right. Much more intuitive than the other way around - we tried. The arms pivot separately along the same axis - each of those tubes has a machined surface for cane creek IS bearings and are also internally relieved to save some weight.

Thanks for all the interest! Keep questions coming if you have them.

kevin
 

·
Registered
Joined
·
1 Posts
Very interesting 'bent, particularly since I've been looking for a FWD design. So I've got some questions:

- What is the angle of the pivot tube and why was it picked?
- How did you determine the length of the rear triangle (from pivot tube to axle)?
- Why lever arm steering instead of something traditional?

I think I have watched all the videos and there appears to be an abruptness to some moderate turns, yet it looks like there's good control in tight turns. Curious.

Really cool.

Thanks!

Marc
 

·
Registered
Joined
·
41 Posts
Very curious to watch and tempting to imagine riding.
I'd sure like to see long videos to get a better idea about stability.

I'd thought that https://www.google.com/search?q=dymaxion+rear+steering+stability had been a problem on a lot of rear-steering vehicles and maybe had some engineering theory suggesting some problems couldn't be solved.

It would be great to see proof in fact kill years of theory on this issue.
 

·
middle ring single track
Joined
·
4,687 Posts
My $.02;

That' a mid-steer recumbent so it won't solve the argument about the feasibility of rear-steer. With F-117 Stealth Fighter-style augmented controls I suppose anything's possible. Or maybe an idiot savant rider.

Well known physics as to why rear steer is so problematic. (especially on a machine that needs active input for lateral stability)
 

·
Registered
Joined
·
8 Posts
Discussion Starter · #18 ·
We were able to ride it one-handed pretty easily. No-hands was hard.

We did take a an advanced dynamics class on single-track vehicle design and control theory. It was pretty clear in the class that there are mathematical models for normal bikes, but none are really complete. For example, we had a model for the "control spring" - the force/deflection of rider input required to initiate turns, but the model wasn't stable on it's own. See here:
Updates to Lords of the Chain Ring are as follows

I'm not saying the math is too hard (actually, yes I am: for a side-project) but I don't think there is a complete model FOR normal bikes or AGAINST rear wheel bikes.

However (and a big one) we suppose that the main centering effect of our vehicle came from mass in the seat, not something dependent on speed. That's the golden ticket - make the stability increase with speed. It's a combo of a centering moment while upright, and a correcting, natural steer towards the direction of lean that keeps normal bikes from dumping you.
 

·
Registered
Joined
·
8 Posts
Discussion Starter · #20 ·
Less stable than an upright, sure. But as you can see from the videos we posted and others out there, they aren't unstable.

I think a better understanding of either uprights or a rear-wheel steer bike could lend information to make these more stable.

It's also a good way to kill creative thinking - by saying that historical failures predict future failures.
 
1 - 20 of 22 Posts
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Top