Trike (recumbent)

Hi Folks, I'm planning to build a recumbent three wheel pedal cycle. It will be a tadpole (two wheels at the front and one at the back).

Now because one usually rides these things feet first :) and drives rear wheels, one usually needs about 5 m of chain with dragging it over jockey wheels and through plastic tubes.

As my feet are near the front wheels, I want to drive those.

Because steering and driving (especially two) wheels, at the same time is constructionally difficult and beyond me in any efficient way, I intend to steer the sole rear wheel and drive only one of the front wheels.

I realise this single wheel drive may tend to affect my steering, but at 60, and unfit, I doubt my maximum 1/4 horsepower will be a problem to correct, especially as the same brain will be causing the power application and the correction :) I will power the left wheel so that it may help to compensate for any camber in the cycle paths.

Now to the rear wheel steer. I've read in the archives of this group that rear steer is considered "unstable". I would suggest that it is very "sensitive". There is an old Canadian rear steer trike that has a sensitivity adjustment. Sensitive for speed, but harsh for slow speed manoevring.

Anyhoo, I will be using 20" BMX wheels for robustness, seeing how they stand up to the punishment that kids deal out to them. I'm wondering about the castor setting for this rear steering wheel. Originally I thought that having zero here would avoid power or braking effects on the steering. But then I wonder if there is no "centering" tendency, the steering might be a bit skittish. There are two angles involved in this adjustment. The angle of the turning axis to the vertical, and the angle that the wheel axle is ahead of this axis of steering rotation. I wonder what effects these have on steering function in this set up.

The other query would be the front two parallel wheels. Should they be set exactly parallel? Or perhaps a little toe in or out, or does this depend on the tyres chosen? (Like a car)

Brakes on the front wheels only will be self compensating by cable to cantilevers on the "forks" applying blocks to the rims.

Reply to
Moosh:]
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Sign up for one of the hpv email lists, these can be found starting at:

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and join your national hpv club (in USA/Canada this is called the HPVA). Lots of information is available.

Rear steer is unstable for several reasons, the worst one is that to catch a rear wheel slide (leading to spin out) you have to steer the rear wheel in the direction that makes the slide worse (increases vehicle yaw rate)--think about it or make a small table top model to play with. Plastic straws and hot melt glue is one good way to make quick models.

Our book (on cars, but tadpole trikes are the same) has a section on steering geometry. Like many text books it is expensive--you can always get your local library to buy a copy.

-- Doug Milliken

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Hi Folks, I'm planning to build a recumbent three wheel pedal cycle.

Reply to
Doug Milliken

One of Golden Fleece awards went to a federally funded project to determine if rear wheel steering on a motorcycle was a good idea. Apparently someone got $100K for the study.

Nevertheless, at low speeds (< 15 mph) rear wheel drive might not be such a big problem.

After all, most >

Reply to
BretCahill

Of course, if you adjust the sensitivity of the steering control to "fine" when doing anything above a crawl, you should be OK. The Honda four wheel steer vehicles have variable control parameters at different speeds.

I was going to have the default "fine" and when I needed gross steering for slow speed manovering, I would lift the steering lever off the "fine" pivot point and mover the rear wheel at will.

Reply to
Moosh:]

But in a normal, front-steer car, you must steer into the skid, which is counter-intuitive. If you don't have ABS brakes, you must ease up on the brake pedal which is again counter-intuitive. We must learn and practice drill these actions.

If your rear wheel steering is set to very fine control, you shouldn't come to grief. From what I can visualise, rear steer is not actually unstable, just ultra-sensitive.

Like normal car steering where the centre range is fine, and the hard-lock ranges are coarse, I would guess that even finer would be OK for rear-steer.

BTW, thanks for you help on this matter.

Reply to
Moosh:]

To reassure the doubtful: we have a juvenile recumbent trike, (from a limited production run) with pedal drive to single front wheel, side stick steer to two rear wheels. It's fun for a kid - doesn't look specially unstable - though it possibly encourages a tendency to scrub tires in a sliding turn.

Brian Whatcott Altus OK

Reply to
Brian Whatcott

Yeah, my kids had "Green Machines" twenty years ago. They tell me at thirty-odd, today, that they were the best fun they ever had. If they could regress, they would buy a new one each today :)

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For an adult version, take a look at the short movies at:
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Reply to
Moosh:]

That sidewinder looks really cute!

Brian w p.s. I just looked over the thread trailing this note.

About the suggesti>>

Reply to
Brian Whatcott

Thanks I will do a search. I've looked at many sites and so far, the Sidewinder

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is the closest to what I am thinking of. It is a bit heavy, and I think I could improve on this with aluminium. I don't see a diff (for two-wheel-drive) as all that necessary, but I'll bet it adds to the weight. I will be using a four-speed-hub-gear in the left front wheel, an intermediate shaft ahead of this taking the chain line to the centreline of the vehicle, where there will be a conventional 3 x 5 derailer transmission to the pedals. This will give me 60 ratios to play with :) The main aim is to get a greatgranny gear at the bottom (15" which is the trans ratio, times the wheel diam) a tall 100" gear at the top for keeping up with the freeway traffic on the downhill :) and a reasonable spread in between -- many redundancies and overlap, of course.

Good tip, thanks for that.

Suspension will not be needed as I won't be going off the paved roads/bikeways.

Interesting. I've heard of rear-steer prototypes fishtailing down the test slope and ending up ontop of the rider :)

Fine for kids, but not so practical for clapped-out old arthritics :)

It's catching, isn't it. I'm obsessed :)

Two wheel recumbents. Yeah, I've got a good mountain bike which I ride wherever possible. I have some difficulty cocking the arthritic hip over the bar. I'm fine once I get going. Getting off is hillarious. I try to stop against a lean rail or fence, but have occasionally missed and slowly toppled sideways to the ground. I usually get the giggles then, and the locals think I'm a bit touched Z:)

Reply to
Moosh:]

Wouldn't it be fun on ice or a skid pan? :)

I agree with the concern, which I have shared. The reason I will try BMX wheels is that others have used them successfully, and they are the "right" size, cheap and probably the toughest wheel commonly available. The spokes are the weak point, I would assume. I will be using conventional axles supported both sides of the wheel by the frame.

Being a sedate old fart (well that's what I try to cultivate :) I won't be exerting "massive" side forces on these wheels. If anyone else breaks 'em, they fix 'em :)

I thought of wheel chair stub axles, but I really want to restrict the construction to common bike parts and the bunch of high tensile aluminium angle I have stashed.

Reply to
Moosh:]

The one I drove was manufactured from aluminum, nice

Sorry, but that is camber, not toe out. Toe out is when the front of the wheels are further apart than the rear. I would suggest zero toe ie wheels parallel. Cars have compliant rubber in their suspension which the trike won't have. Parallel wheels give lowest rolling resistance. Camber as you have described (negative) is a good idea. It helps stop tyres rolling off rims and puts more of the cornering force into compresion/tension in the wheel. Not really my scene, but ISTR I have seen BMX bikes with one piece plastic wheels, ie no spokes. Would these resist cornering forces better?

John

Reply to
John Manders

Interesting idea. Here's a couple of thoughts. When recumbent, a persons C of G is towards his upper trunk. This means that the front wheels carry less than 1/2 the weight. If you only drive one of them you may suffer from lack of traction on hills. This is then accentuated as there is weight transference to the rear wheel. Since the front wheels are not going to steer, how about having them fixed to a common axle shaft giving 2 wheel drive but with no differential. Now if the axle is cranked between the wheels, you have your pedals and you C of G is well forward. Of course this idea may be unworkable for reasons which I cannot see as I'm not a keen cyclist. Second thought. The current world land speed record holder (and the only car to exceed Mach 1) is rear wheel steer. ISTR that they had some fairly powerfull stability control electronics on the car, but why let that spoil an interesting comparison.

John

Reply to
John Manders

You can stick your backside directly over the front axle centrelines to keep weight over the front wheels, but my peddling will be lucky to ever spin wheels. I'll take a photo and be proud of it :)

Fixed wheels would be a disaster for tyre scrub, I would have thought. Even having one with a ratchet would be problematic providing no drive to the outside wheel on cornering. Just the wheel that a differential favours in a car.

I've tried mental gymnastics trying to figure out a way to drive the wheels and have finally settled on the design I have outlined. It is doable, and cheap, and worth a try. I have lots of the parts and intend to scrounge most of the remaining from the ready supply of old bikes that folk throw out on their verge for rubbish collection :)

Reply to
Moosh:]

Well, could you explain? I can't see that front or rear is more stable than each other. Stability surely implies that the system will remain as you left it. This surely depends on caster angles and "axle offset". I don't know what else to call it. The distance the axle axis is away from the steering rotation axis.

Anyway, if you set up a front-steering wheel with zero castor angle and the axle axis intersecting the steering rotation axis, it would be just as unstable as a similarly set up rear-steering wheel. Please explain the difference.

As far as sensitivity goes, because rear steering has much greater directional consequences for each degree of movement from the straight ahead position, it requires a much finer control mechanism.

Am I wrong? I would so like to learn what it's all about.

I will, thanks Fred. Did you get to have a squizzy at the Sidewinder clip?

Reply to
Moosh:]

If you build a rear steer vehicle you may find out about the stability problem as you coast down a hill....

I would sugest you try reading "Car Suspension & Handling", D.Bastow, section 2.12 before you start. ( explains why the steering will suddenly try to jerk out of your hands. )

BTW if you are going to make a trike for anyone other than yourself I suggest you look into public liability insurance.......

-- Jonathan

Barnes's theorem; for every foolproof device there is a fool greater than the proof.

To reply remove AT

Reply to
Jonathan Barnes

So you can't explain it in simple terms? I've reversed many a car at speed, and have had no problems. And reversing a car is driving the steered wheels in the opposite direction to that in which they have been set up to run.

I intend to set my steered wheel up correctly for forward travel.

Never had that happen. I wonder why it would.

Have a look at the Sidewinder clip. Movie 2 is called "Solo spinning" for obvious reasons. It's small enough to fit on a floppy disk.

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That surely goes for making anything for somebody else.

I take it you didn't look at the Sidewinder site? I guess they have the same public liability insurance as any other cycle manufacturer.

Reply to
Moosh:]

Check out

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- maybe front wheel drive/steer wouldn't be all that tough....

Reply to
Steve Rauenbuehler

All rubber is deformable, so when it is used in car suspension it can compress when loaded. This can change the wheel alignment so a case can be made to set the wheels "out" of static alignment so that they move into the "correct" position when the car is in use. The amount of movement and it's direction varies from car to car so there are few standard settings. Good point about the wheel chairs, I had forgotten about them.

John

Reply to
John Manders

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