View Full Version : Tadpole Rear Wheel Steering?
04-20-2013, 01:55 AM
Has anyone tried rear wheel steering on a tadpole style bike? Wouldn't the front wheels be able to remain perpendicular to the ground with no akerman? Would it be possible to drive both front wheels from a drive shaft connected to the cassette in the center?
04-20-2013, 05:34 AM
I'd avoid RWS like the plague unless you fully understand all the inherent disadvantages it offers and are confident of at least taming them with clever engineering. RWS offers a very tail happy experience with the rear moving towards what you are trying to steer away from! You will be very likely to spin the trike assuming you don't flip it. Fork lift trucks employ RWS for manoeuvrability but never travel above a few mph. As a bare minimum you'd need to move the rider far forward to try to induce a designed in understeer to counteract the rear's oversteer characteristics. This then has an unwelcome effect on braking unless you have a very long wheel base.
2WD is unnecessary. 1WD works perfectly well and linking the front two on a solid axle will create tyre scrub in any corner.
04-20-2013, 10:34 AM
Yes, RWS is a nightmare to control at even moderate speeds. There was a trike called the "SideWinder" produced, but not sure if it still is.
Besides flipping right over very easily, RWS trikes have another serious issue... rear swing.
Let's say you are needing to quickly maneuver around a parked car. On a normal FW steered trike, you crank the steering, lean a bit, and probably make it around.
On a RW steered trike, you crank the steering and then ass end is swung directly at the object you aim to avoid, working totally against you. You will collide with incredible force.
For a fun trike or just an experiment, go for it! But don't expect a street safe and stable ride no matter how much engineering you put into it.
04-20-2013, 10:36 AM
POpshot is basically correct.
But I reserve judgement when it comes to comparing to a fork lift, even though there are similarities.
The main problem with a fork lift is nnot actually in thye rear bwheel steering--its in the very heavy weights added at the rear to enable it to lift heavey loads at the front! If you turn too quick, the rear wheels push the back off line, and , especially if power is reduced or brakes touched, all that weight then tries to keep going--instant spin out. happens quicker than I write this. Now how do I know--engineering training combined with practical experience--been there --done that.
I see no advantage in a tadpole with rear wheel steering--it is just introducing complications to the drive train, which ever wheel is being driven.
Equally, it is unfair to compare a properly engineered trike to a fork lift. There is at least one example in the gallery of a successful rear wheel steered DELTA trike, and it is a nice piece of engineering.
I actually rebuoilt the front end of a VW to steer in reverse at high speed--it worked well backwards, and was just managable forwards, but needed power steering in sand. Nothing wrong with rear wheel steering done the right way---but the right way is a hard learning curve!
04-20-2013, 11:59 AM
To Answer questions-
Is the site that had designed a rear steer recumbent. Also a member here built a rear steering using as a hand driven cycle out of Africa. But his video looked like it was somewhat akward to steer. He was building for a handicapped friend.
Utah trikes has a video of the sidewinder but I no longer see them for sale from that site.
Front wheel drive is possible and has been used with a differential to drive both wheels using a Samaga differential according to the Utah trikes video. There was a Russian Trike that also used a differential for front wheel drive on a tadpole and I remember a quad with all wheel drive once again using differential of some sort to drive all the wheels.
Enjoy searching and let us know or show us how it is done. Your choice. Welcome to the group.
04-21-2013, 12:39 AM
Sidewinder has been out of business for about a year now. Not a bad trike IF you kept it below about 20mph. Anything over that and you would loose control. The steering design was all wrong for faster riding; that's why they did not sell. Rear wheel steering DOES work as I have built a 2 wheel design and am currently getting things powder coated to finish it. Been working on it for about a year or so now. The learning curve is different from other bikes/trikes and is a total blast to ride. IMO, the biggest complaint with most of the tadpole trikes out there is that they are too short of wheelbase causing poor weight distribution f-r and the caster angle needs adjustment for stable operation. A rear wheel steering tadpole would require a lot of design work as you can not lean it as you can a 2-wheel bike, unless you make it a tilting/leaning design. You would have an extra wheel in front causing drag while turning and that would have a lot of bearing on the design; no Ackermann steering. A forklift is designed to turn fast and tight at speeds of 8-MPH OR LESS and without going into detail lacks the necessary "design" to go faster safely. Just like a typical DF bike, if the "relation" of the head tube angle, wheel size and rake are "off" good luck have a stable ride.
04-22-2013, 03:38 AM
I like the sidewinder, would adding a steering damper make it safer at higher speeds it would seem so?
04-22-2013, 11:25 AM
IMO, NO. The steering design will not allow stable high speed riding no matter what you do.
04-22-2013, 12:34 PM
Not only this idea playing with fire from the stability/safety issue, I fail to see the advantage in trying to steer the back of a tadpole when it must cause complication to an otherwise simple drivetrain, --almost impossible for rear wheel drive, as chains don't like bending, and front wheel drive which would have to have some sort of differential to make it work safely.
And there is not much room for a drive axle on a tadpole unless the rider is placed on a higher seat, thus reducing stability again.
Interesting idea, but one which should stay on paper, as the results ared almost predictable, unless there is a magic way round the problems.
On a Delta trike, its been done, and seems to work, with a very simple drive train, and steering no more difficult than a Warrier (in fact easier)
But don't confuse the two concepts.
And I agree with Irv ,that a steering damper will not push the problems under the carpet. Dampers usually only hide an in built problem some where else!
04-23-2013, 11:55 AM
I'm familiar with dampers used on motorcycle steering. They are generally used to mask an inherent engineering failure
04-23-2013, 12:05 PM
For coming out with the truth!!!
I tried to say this earlier-- a damper only hides a problem the designer /builder could not slove ( been there --done that)
Under controled conditions, can be a solution---but let loose on the public, is far from an answer.
04-23-2013, 03:53 PM
How about do a google for Velayo velomobile, if you can read German even better. I found that quite by accident and had to really search for it again.
There are some videos of it knocking about YouTube, it looks very stable to me, but the rear wheel has some clever geometry going on with the steering mechanism.
As to effectively driving backwards, I used to push a trolly round where I used to work that was 'rear steering' everyone pulls them usually. At first it's difficult but I got use to it that you could be precise.
04-24-2013, 03:11 AM
Thanks for all the good information, I'll skip rear steering for now but I am definitely going to build one for slow speed fun. Do you remember the Krazy Kar? The Krazy Kar was a blast when I was a kid.
04-27-2013, 06:32 AM
Trainhound, seems that you've come to your conclusion already, but I'll just throw my two cents in anyways.
I built a rear steering handcycle that I thought worked pretty well at low speeds (see it in action here: http://www.youtube.com/watch?v=CNvqUIasL40 ), but the friend that I built it for couldn't get the hang of it and it's just sitting around not getting used. I did a bit of cheating by adding rubber straps to keep it going straight when you aren't steering, but to be honest (as others have said) this was to just cover up a problem that I couldn't solve. And the scary thing is that my friend has to travel over this bridge if he wants to go anywhere, which makes me really nervous about one of the rubber straps snapping at the wrong time.
Anyways, if I was going to do it again (or rather, the next time I do it), I'd forget the rear steering.
The Gambia, West Africa
04-27-2013, 09:35 AM
The advantage of building for fun is that it does not matter if it works, its still fun, and you may learn the magic secret of how to make it work. If you don't you did it for fun!
But do share the story as we all learn from each other.
I personally don't think it will work as a practical everyday trike, and see no point in the complications--which are many--compared to a "normal" tadpole.'
But don't listen to me if you just want to have fun, because the quickest way to get me to do something is to tell me it can't be done!!