Rear wheel steering

Discussion in 'Motorized Trikes' started by khillr48, Jun 10, 2009.

  1. khillr48

    khillr48 New Member

    I went to rear wheel steering in order to keep the front wheels narrow. I wanted to be able to fit thru a normal door. As I mentioned, I had a lot of interests from seniors, both for ease of getting on and off the trike and storage. I've used this type of steering on several projects over the years. It works well. As you can see in the picture a rod connects one steering arm to the wheel and the two steering arms are connected with a push/pull cable. Like the ones used on boats and watercraft. The steering pivot at the wheel is similar to that used on gokarts. I make adjustable castor because the torque of the drive on the wheel would torque the steering. With a little negative castor the steering under takeoff power was neutral.
    Hope this helps srdavo.
     

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  2. SimpleSimon

    SimpleSimon Active Member

    Interesting. I'd really like to see additional pictures of that system from various angles, and perhaps a couple shots from far enough back to clearly see the entire ride - preferably with the steering angled to more clearly show its workings.

    I drove a street sweeper many years ago at a lumber mill, cleaning up the storage yard. It had single rear wheel pivot steering, and took some real getting used to.
     
  3. khillr48

    khillr48 New Member

    Happy to send more pictures but it will be a few days. I just started a new job and the trike is at another location.
    The short wheelbase keeps the steering from being to odd. It is a little different in tight spots. But I made it for low speed. I'd like to try the motor drive in the hub of the wheel and add pedal power too. These electric bike drives aren't powerful enough by themselves.
     

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  4. SimpleSimon

    SimpleSimon Active Member

    I'd definitely like to see them. I've been toying with designing an under seat steering linkage that it "joystick" controlled - I have only one hand, and most direct steer systems won't work very well for me. Along with the side-to-side gymbal action for steering, I'd like it to be set up to activate the brakes by hauling back on it. That way, I can much more easily control the clutch and throttle one handedly.
     
  5. khillr48

    khillr48 New Member

    Simon
    One of the first trikes I built had a joystick steering between the legs but it steered the front two wheels. I'm sure the push-pull cable would control the rear wheel steering. Maybe hydraulic brake for pull back action. Throttle and clutch too, that's a lot going on. Maybe some foot action for some of it? Anything is possible. Any designs yet? Gas motor and how fast do you want to go?
     
  6. SimpleSimon

    SimpleSimon Active Member

    khillr48, fast isn't an issue for me. A tadpole trike at 25 mph is more than fast enough, a delta at 15. I'm a fairly big guy (5' 11", 240), but I have serious physical limitations that are taxing my imagination to solve. Along with only one hand, I have severe diabetes, which has resulted in neuropathy in my extremities - I can't feel anything below my knees, and I only have full use of one finger and my thumb. The second finger works well enough for typing and lite tasks as long as I can see where it is being put, but I have to be pretty careful where it is going when working on things. Because of the neuropathy and other metabolic issues accompanying diabetes, I can't pedal hard or very long. So, power assist is a practical necessity.

    Not an attempt to elicit pity; I say the above because as part of my physical reality I have to make allowance for the limitations in accomplishing things.

    I design things - always have, since I was a kid. I've designed and built a lot of things, from toys to sculptures to houses and their furnishings. Now, my income and living circumstances leave me with no working space save my living room floor in a second floor apartment, with minimal hand tools. So, projects take a frustratingly long time to reach fruition. Oh well, c'est la vie, eh?

    That said, my greatest assett in life is a truly monumental pigheaded persistence. I just keep plodding along, doing what needs to be done to accomplish my goals.. Right now, one of my high priority goals is getting out of that econobox I use for transport, and getting my face back into the wind. What I really, really want is a leaning tadpole trike, with full suspension and optimized steering engineering. Since I'm utterly uneducated as an engineer, I've been doing what I have always done - design my dream after learning all I can find about the project and materials, tweak the design, set it aside while things percolate in my head, and tweaking the design some more.

    The rear steering idea has raised the heat in that percolator till it is popping like the old Maxwell house coffee commercial. In my minds eye I can see a tadpole trike with power to the front wheels through both pedals and engine assist, feeding a "differential" and each wheel seperately, with a limited caster range central rear wheel doing the steering. Thank you for getting me thinking in a different direction than I have in the past - for myself, finding and implementing workable solutions has always been "Job One". The world is designed and built for two-handed people with well working legs, so I have had to evolve my own approaches to problems.

    You rear steering system intrigues me, and seems it may be a near ideal solution to one of the biggest issues I've encountered.
     
  7. jawnn

    jawnn Member

    Long rear steered trikes

    I am thinking of changing my trike to a 'rear steer' by turning the trike around and putting a boom with crank out the front that was the back.:idea:

    But I am worried about the handling of the steering; the back that was the front will swing out on sharp turns.

    The only reason to do this is the added room I would have behind the seat, and maybe a little more stability in turns?.
     
    Last edited: Jun 13, 2009
  8. khillr48

    khillr48 New Member

    Simplesimon
    That is a lot to engineer. I'm going to have to look into how to tilt. The suspension should be interesting. I bought a differential from Northern Tools for a gokart a long time ago. It weighs a little but for low power it will work. I've considered using it myself. I tried it in a kart, it's not limit slip or posi so you have to put a brake on each side. The axles are 1". A lot to think about. But nothing is impossible. With all these moving parts, this thing could be heavy. Might consider enough horsepower to do it all. Especially if you have many elevation changes where you are going to ride. I can envision combining the tiller steering/brakes/tilting. Even suspending the rear wheel steering like mine. Maybe a small scooter drive like a Honda Elite on the rear? Have to give that some more thought. Keep thinking and make some drawings, might think of something new or find out that something may not work.


    Jawnn
    The first tadpole I built with rear wheel steering I tried with a bike front end. It was a steering linkage nightmare. Castor is important and like you thought can be squirrelly . Another caution is wheel base. I shortened mine because it would flip over until I shortened it. Of course my front tires are only 29" O.D. If width isn't a problem it helps along with low center of gravity.
     
  9. SimpleSimon

    SimpleSimon Active Member

    Bike differential issues is a problem long ago solved. Schwinn used to sell an upright delta trike with a differential set up. Nor is it terribly bulky or heay, You need 4 sprockets of the same size, two of them set up to freewheel - one left hand, one right hand. The two fixed sprockets go on a jackshaft, that has the final drive sprocket on the right hand end (for pedal systems), the two freewheel sprockets go on the inner ends of half axles, each co-planar with one of the jackshaft mounted sprockets.. You can also readily set up your braking system there, as well (disc brakes preferable).

    One nice thing about this system is that you can use a multi-speed internally geared hub as the jackshaft, with ring sprockets mounting to the spoke flanges, which in effect gives you a multi-speed fifth member mid-drive. I am in the process of modifying a Shimano three-speed hub to hold ring sprockets I fabbed from small crank sprockets, but I'm still looking for a good source of a left side freewheel for the left half axle of my trike adaptor.

    That had a solid axle with a single sprocket intended to drive the right wheel only, while the left wheel was intended to be just a bearing shell that slides over the axle. I've modified it by cutting that one inch diameter central axle portion at center with a hacksaw - not as bad a job as it might have been because I mounted a hacksaw frame on a pivot and hung 5 lbs on the other end, got it aligned with the center of the axle and started spinning the axle from the end with an electric drill on slow speed. I used the same process to cut a lock groove for a big C clip on the left half axle to retain the axle alignment. That runs against a UHMW disk I cut on the scroll saw to fit over the axle snugly.

    There are almost always ways to adapt anything to do the needed job, it's mostly a question of implmentation. The differential described above lets the outside wheel in a cornering situation spin more quickly than the diven axle is turning the inboard wheel, which ends wheel scuffing and the problem of only powering one side or the other.
     
  10. khillr48

    khillr48 New Member

    Simplesimon
    I'm not familiar with the Schwinn diff. I'd like to see one to follow what your doing. I have access to a machine shop, so if I can help let me know. I recently made a few freewheel adapters to a 3/4" shaft for a front wheel drive I'm working on for my trike. It's always time and money issues. I'll try and get a few pictures soon.
     
  11. SimpleSimon

    SimpleSimon Active Member

    Here's a pic of my first pass 3D model of a short wheel-base (3 feet), narrow track (26") rear suspension only, rear steering tadpole trike. Crank boom out front, main chain loop (gold translucency) back to a Shimano 3 speed hub, with sprockets replacing the spoke flanges. Those sprockets then drive the secondary chain loops (pale blue cross-hatched translucency) to the two freewheel capable sprockets at the inner ends of the half axles. Wheels are fixed to rotate with the axles, disc brakes mount to the inside faces of the wheels, both sides. Although not yet drawn in, the rear suspension is intended to be a suspension fork, mounted at the proper caster angle for Ackerman geometry - in this case 18.4 degrees off vertical. Steering I intend to do much as it is done in light aircraft - cased cable led in curves around the frame and crossing in front of the top of the rear fork mount, so when the T=bar yoke is turned left, the rear wheel pivots to the right, and vice versa. By virtue of the inletted tube steering uprights contraints, steering will be a maximum of 45 degrees each way.

    The attached pic is a view from under the frame, showing the "differential" I spoke of before
     

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  12. khillr48

    khillr48 New Member

    Simon
    Here's some cropped pictures. Hope these will be of help. The hexagon nut under the head of king pin bolt is an eccentric, the hole is drilled offset of center, by twisting you can adjust castor/camber and with one on the bottom even more adjustment can be had. There are bearings top and bottom in the frame tube. As you can see a solid rod to the right steering arm and a cable with solid end rods connect the right and left steering arms.
     

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  13. srdavo

    srdavo Active Member

    omg, guys..... keep up the good thread!!

    Being a forklift operator, I have been interested in rear steering, since I saw the 'sidewinder' trikes. Not sure if the company is still in business.

    I don't have a lot to add here...maybe questions..... but I am trying to soak all this up!!

    thanks....carry on!! :D
     
  14. SimpleSimon

    SimpleSimon Active Member

    khillr, I think I must be blind or something, but looking at those pics I can't figure the steering linkage out. Sure, the push rod to the pittman arm on the eccentric cam action right side axis of rotation I understand - that's just geometry. What I'm not following is what's going on with the left side mount.

    The push rod/cable pull action I follow, but if the vertical axis of rotation is the offset cam nut eccentric on the right, I dont see how you can have ANY fixed point on the left - the left end of the axle HAS to describe an arc, determined by the eccentric cams rotation and the opposite end of the axles distance from that vertical axis.. If the axle length is 3", then that left end MUST swing through 3+ inches of travel in a streering system coonstrained to a max turn of 30 degrees each way.

    Now, I see how one might set such up, but the pictures don't show your left side at all, and the size of those spokes and hub completely obscures the view of the left sides support.

    If the wheel is supported only from the right, then no problem.
     
  15. khillr48

    khillr48 New Member

    Simplesimon, sorry I don't have any pictures of the left side. There is nothing attached on the left. Just a matching frame that stops short of the wheel. Thanks for the picture, I printed it and your description to study. I remembered my son has my grandfathers Schwinn 3-wheeler. It must be over be over 30-40 years old. It's in pretty good shape except for a bent rim and being outdoors for a while. I'm going to snag it for study. Maybe refurbish it, it's to old and nice to cut it up.
     
  16. SimpleSimon

    SimpleSimon Active Member

    Well, here I am again, drawing pictures. I decided to actually do some calculating of forces on the frame of a rear steering trike - man, I really hate vector analysis!

    It's necessary sometimes, and because I really am not an engineer and I really am not certain my calculations are correct, I use a safety factor of 2X. This design was aimed at simplcity combined with aesthetics - I prefer organic curves to sharp edges and corners - and happily, curved tubing is actually stronger across a given cross-section than is the same tubing straight. In theory, the entirety of the main frame could be made from one continuous run of 1" by 1/16" wall cromolloy tubing, although I doubt anyone would try.

    Rear wheel is 26", for several reasons, and design constrained to a maximum pivot of 45 degrees off center. That makes the width of the frame at its widest point 29.75 inches. Wheelbase is actually 26" OD front, by 36" long, giving an Ackerman angle of 19.9 degrees. Power is pedals back to an NV Hub, then forward to seperate freewheel equipped half axles. There is room behind the seat (not shown) for an engine, to provide power through the NV hubs secondary input sprocket.

    Not shown is the actual seat - I wire framed its skeleton, becaise otherwise the mechanicals would be obscured.
     

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