Rear-Wheel-Steering Recumbent Bike Prototype Testing

Part of our Cal Poly senior project. This is the prototype for a bike that will compete in the 2010 Human Powered Vehicle competition in 2010.
http://www.asme.org/Events/Contests/HPV/Human_Powered_Vehicle.cfm

Many of the features are adjustable, including the head tube angle (the angle of the hinge), the wheelbase by multiple dropouts for the front and rear wheels, the control sensitivity by the lever-arm linkages, and the seat position.

Partial credit for this design goes to Dennis Renner, for giving us the initial idea of a rear-wheel-steered recumbent.
http://www.youtube.com/watch?v=KMA7CTfbpwo

Before this one, we constructed a proof of concept bike, with no pedals, and a different steering mechanism.
http://www.youtube.com/watch?v=gBR-rPoZlsg

By adjusting the head tube angle on our prototype, we discovered that a forward angle gives us better stability at high speeds.

See footage of our final bike on this channel: http://www.youtube.com/user/moynihanigan

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[cbulen]

How come Denrnr's RWSFWD recumbent seems more stable that yours? He mentioned that your group contacted him for info on his bike.

[FatalNoogie]

@cbulen There are a lot of factors in play. Because some features are adjustable, each time we changed something, we had to get used to riding all over again. This configuration sacrifices stability for agility: hence the really tight turns you see in this video. The prototype is also much heavier than the Renner bike, and heavier than our final bike. You can see videos of our final bike on the channel for user moynihanigan

[wolfekeeper]

Steering geometry looks wrong to me; for RWS the trail point of the rear wheel is supposed to be in front of the front wheel. You can do that with the proper linkages or by having the steering axis point there.

[FatalNoogie]

@wolfekeeper To do that on this bike (with the adjustable head tube) would put the head tube almost horizontal, so I don't see how the back wheel could even turn side to side with so little rotation about the vertical axis. I'd need to see an example to understand what you describe.

In any case, the project was finished some time ago. I'll post links in the description.

[vistigioful]

Cool.

[cbulen]

@FatalNoogie

Cornelius suggested that a 4-bar linkage (pivots oriented vertically) might solve the low balance speed (he called it CBS-critical balance speed) as it would give the bike a long "virtual" trail for the rear wheel placing the instant center far forward. (see pg20 of his article in IHPVA. I am thinking of trying non-parallel 4-bar, with the instant center far forward of the rear wheel. Did you guys explore that?

[iamtheoriginalcody]

Wow I can't believe the low speed stability over most rear steer diamond frames. Love the adjustability you built in also. Will you be at the east coast event also?

[raftmant]

Hi!

I plan to build a rear wheel steer recumbent , but in videos it seems so unstable. Is it stable in high speeds? Can it be driven hands off ? I tought maybe in video it seems unstable becuse of the rider sits above the wheel center? Can anyone help?

thanks!

[COMB0RICO]

NEATO!

[cbulen]

Oh yeah, I should add: A correction to the article was printed in the issue that followed. Vol8 no 1, page 3