Comments on: Mohsen Saleh’s RWS recumbent

By: Mohsen

Mohsen — Sat, 24 Mar 2012 01:37:22 +0000

Thank you Jeremy for sharing your opinion.
I like your front steerer…
Peter Eland already shared this project with us in previous comments and I liked what you did in your design….would love to ride it to learn more about its handling.

By: Jeremy Garnet

Jeremy Garnet — Thu, 15 Mar 2012 13:49:11 +0000

I think the reason that rear-steered parallelogram linkages work on paper, but less so in practice, is because auto-stability is not merely a matter of turning into the lean and centering the wheel by its rolling resistance. Stability is also concerned with the correct response to sideways forces from ridges and road imperfections that approach the wheel from an angle. When a steered wheel encounters a small ridge or imperfection in the road at a small approach angle, it will deflect the wheel sideways, away from the ridge. If the steering geometry does not turn the wheel into the ridge, so as to ride up and over it, there will be instability. On a front-steerer, the geometry that will do this is the same as that required for a correct lean-steer response. In other words the “lean steer effect” is synchronized with the “ride up on a side ridge” effect. This is a requirement for real-world stability. I don’t think this can be done with a rear-steered bicycle.

The main advantage of rear wheel steering for a direct drive recumbent is the absence of any pedal force feedback to the handlebars. However with careful design the feedback to the handlebars on a front-steerer can be reduced to as little as 12 percent of the applied pedal load (see my HP article link below). This level of feedback is completely manageable. In fact, I have ridden a non-optimized direct-drive recumbent many kilometres without experiencing much of a problem managing the pedal loads. This is because the rider’s feet naturally produce an laterally outward pedal force which tends to negate the force feedback to the handlebars.

http://www.hupi.org/HPeJ/0017/GarnetDirectDriveRecumbents.pdf

By: Mohsen

Mohsen — Tue, 13 Mar 2012 22:38:58 +0000

Hi Craig
Thank you for responding to this post, i have read your story of rear wheel steering and I tried to find a contact from you, I have actually quoted from you in my blog,
I saw a parallelogram wheel positioning in HPV magazine but as my concept was about a linkage with different configuration i assumed that i might have found the solution.
The common ground in bicycle dynamic is that the bike should steer into fall direction in order to have auto stability, on paper it seemed that i would achieve auto stability however in practice it wasn’t. I had the concept for a year.and i felt that i have to do it… it took me a a month to design the details and 2 weeks to build. Was worth trying though.

By: Hephaestus

Hephaestus — Sun, 11 Mar 2012 19:41:17 +0000

Ah the lure of a rear-steered recumbent bicycle. I spent 10 years building prototypes and testing. After which I published what I hoped was a definitive article in “Human Power” so that others didn’t have to start from scratch on the problem. Alas that was back in 1990.
http://www.ihpva.org/HParchive/PDF/27-v8vn1-2-1990.pdf
Pages 6-7 &17-20. This should help you understand the design space a bit better.

When I finished I had a vehicle that could be ridden at moderate to high speeds but could not be balanced at very low speeds. I did a 50 mile ride on it but had trouble negotiating through walking traffic.

I do not believe either a single pivot or a four-bar linkage design can produce the auto-stability you need for easy starts and very low speed maneuvering. My first prototype had a four-bar like the one on your post with the instant center behind the contact patch of the wheel. It couldn’t be ridden. All the prototypes that worked had very long trails with the pivot in front of the wheel’s contact patch.

Regarding the hub drive, it is very clean and compact. Unfortunately, if the vehicle wheelbase is a reasonable length, the drive wheel is too lightly loaded. You don’t achieve the 55-60% loading you need for good traction.

http://www.lefthandedcyclist@blogspot.com

By: Andy

Andy — Wed, 08 Feb 2012 21:27:14 +0000

And there’s most of bicycle design in a nutshell. They assume that if something isn’t widespread today, then they should create it themselves, only to fall into the same pit that previous designers did. Only the truly useful concepts emerge, and those are very few.

By: Mark Swartz

Mark Swartz — Wed, 08 Feb 2012 21:16:20 +0000

Rear steering designs keep on getting recycled ad infinitium. Unfortunately, they never go away as someone working in isolation will identify supposed ‘problems’, and then go and find supposed miraculous solutions in the form of ridiculous designs that require unique riding skills and present new dangers, i.e., case in point, rear steering. I should know, I’ve ridden and even owned one ( the Vacuum Velocipede). The design in this post looks very similar to a trike built and flogged by the Thebis company in Toronto during the 1980′s. Ask yourself why you don’t see rear steered bikes or trikes succeed in the marketplace. Darwin is right.

By: Cycling’s Week on the Web - Bike Rumor

Cycling’s Week on the Web - Bike Rumor — Sun, 05 Feb 2012 02:47:45 +0000

[...] the pros and cons of his prototype and what he plans to change in future designs. Thanks to Bicycledesign.net for the coverage of [...]

By: Mohsen

Mohsen — Sat, 04 Feb 2012 09:28:21 +0000

Thank you Wuss and Petter for the links

Andy!!! I do have sympathy with you about hub-less designs, and if i dont manage to stable this bike i would agree with you also for RWS one as well. take it as an experiment…

Thank you Mike,

@Victor…you are right, stability is the main issue with RWS designs, and actually the main reason that i began building this prototype was to investigate stability of my 4 bar linked steering mechanism. the first try was not as i expected but I am hopeful that with this configuration i would be able to build a bike that is stable in low speed as well as higher one.

By: Peter Eland

Peter Eland — Sat, 04 Feb 2012 09:07:16 +0000

Victor, the Rohloff is a lovely hub but how would it fit into a front drive like this? The pedals need to be attached to the same axis as the hub axle, and to rotate together. The axle joining them needs to be pretty hefty to resist pedalling forces, and the frame attachment also needs to be completely different (similar to a unicycle, hence the first comment). You would have to fundamentally redesign it, in fact the R&D effort would be no less than for making an entire new hub gear.

ISTR that Kretchmer (referenced in the HUPI link above) did actually propose a suitable hub gear design with dimensioned drawings back in the late ’90s – it’ll be in his patents somewhere. But getting a working hub gear made is beyond the resources of most experimenters.

BTW the Velayo is a commercially available rear steer trike which seems stable up to pretty good speeds, using a more elaborate linkage: scroll down to the last picture in the first link below for a look – not shown well on their own website.

http://www.velovision.com/showStory.php?storynum=1011

http://www.fortschritt-fahrzeugbau.de/produktkonzept.htm

By: Victor Ragusila

Victor Ragusila — Sat, 04 Feb 2012 02:25:45 +0000

Also as a follow-up, a modified Rolhoff might be really neat as a transmission system. Right now the 1:1 gear is the 11th, and most are slower. If there is a way to modify the hub such that it starts from 1:1 and goes to 1:5.1 it would make this transmission very nice and efficient.