I wanted to build a bolt-on rear that would allow me to test various degrees of wheel camber without destroying my original, simple and light weight flange setup. I also wanted to see what effect suspension would have with the bump steer issue, so I figured out a way to combine both suspension and an adjustable camber into one unit that fastens onto the frame with two bolts through the old flanges.
Basically, the way it works is the shaft that runs from the left wheel to the right wheel is hinged in the middle and bolted onto the old shaft through two slots - like shown below:
Then the hinged axle is held horizontal by stretching two rubber bungie straps around the tube and up to the cross brace on the subframe.
When downward pressure is applied to the seat (hitting a bump), then the sub frame is forced down which bends the hinged axle and stretches the elastic straps. Since this hinged axle is bolted onto the sub frame through two slots cut into the hinged axle, it allows the wheel contact patches to stay where they were, and the top of each wheels rotates inward. If I had not provided the slots, then each down force of the frame would push outward on each wheel causing the wheels to skid sideways across the pavement. This way the wheels are free to camber with the contact patches staying on the ground.
To "lock-in" a starting camber I added a threaded rod mounted to the sub frame axle. This allows me to adjust the minimum camber as shown below:
I haven't yet given it a good test ride - I took it around the block a few times and it felt fine. I even ran it over my 2x4 and didn't feel any bump steer. (Currently there is a foot of fresh snow on the ground!) The plan is to take it out to hwy 22 when the weather clears and run the following tests:
1. Ave speed at 150 watts with no camber (wheels vertical as before) and suspension
2. Ave speed at 150 watts with 10, 20 and 30 degrees of camber
3. Note rumble strip bump steer effect at each camber setting
4. Roll-over speed test at each camber setting (might simulate this by tipping over the trike while sitting on a sheet of plywood)
After those tests I will know for sure how much suspension helps with stability and what the efficiency cost is. I'll also know how much extra cornering force I can attain with various degrees of camber, and the resulting efficiency cost of each.
Also - there may be an interesting side-benefit to this method of suspension, and that is during high-g cornering, the force may push down on the frame causing the wheels to increase their camber which would result in more stability during the turn. Also, the g force during a turn would lower the center of gravity thereby increasing stability even more.
That would be ideal, as I could keep the wheel camber at 0 when travelling straight (perfectly vertical and most efficient), then only during a corner would the wheels camber. If this works the way I hope, then I would have the best of all worlds - suspension to eliminate bump steer, efficiency for straight travel, and better high speed cornering stability with the automatic cambering suspension.
If this works, then I would probably ask Ben Eadie (check out the bikes he's building at his web site) to redesign it all making it slide better and lighter while maintaining the basic principals. Currently, it's not as smooth as I'd like it to be - I need to use a lot of grease on the rubbing metal parts.
My thinking at this point is that this cambering suspension system (if it works) would probably have to be a part of a rugged cross country machine - the TRANSCANADA rocket. Allthough I am having some issues with shoulder travel and permits, etc, I am still proceeding with development as if all systems were go. Kevin Thompson (creative crossings society of Canada) is looking into provincial permit issues now. As far as any intermediate goals for me and TCR1 (like a possible distance or speed record attempt): I would be inclined to revert back to the simple 31" rear end without any extra complexity or weight of this camber/suspension system.
Meanwhile, Ben and I are still looking into changing the push/pull cable steering system to a worm gear based contraption. The biggest reason for the cable steering is to have some method of steering when the fairing is on. If I were to rely only on leaning to steer, it might be very difficult with a tight fitting fairing. The second reason for the steering system is to stiffen the pivot when steering is not required. This removes all peddle induced wobble, unwanted oscillations, and eases bump steer. When I combine with cable steering with the steering brake, it allows me to lock-out the pivot completely for an ultra stiff frame while cranking hard and high speed maneuvering. Basically, what I'm trying to accomplish with the brake and the cable steering is to eliminate any feedback from the road - this is why I am looking into a worm gear system. Worm gears allow work transmission ONE-WAY - from the steering input to the worm to the gear and eliminate any feedback because the gear cannot turn the worm. It would be like having the steering brake fully engaged until a steering input was required.
Ben had this brilliant idea to use a NFB (no feedback) steering system from a motor boat. Boats handle better when the rudder is not back-effected by waves and currents. We're looking into it, but these systems may be way too heavy for my application.
Too Dooo LIST:
1. Buy and install right brake (FINALLY ordered it!)
2. Invent new cable tensioner to allow more steering bar turn radius3. Add front derailleur
4. Order 20mm axle bolts for the rear wheels (I'm using 1/2 inch now which isn't right)5. Design and machine 2 seat mounts out of aluminum to replace current steel ones (e-machineshop.com) LATER.
6. Design and machine 2 steering tensioners out of alum to replace LATER
7. Order a new front wheel! (Helen is kind of upset that I am user her Zipp race wheel!)
8. Start work on the first fairing (starting now)
9. Invent steering stiffener10. Add larger chain ring
and modify chain stays12. Fabricate new steering bar (aluminum or composite?) or rework existing
11. Make clamp-on out riggers and try to flip it (changed to#25)
13. Lathe an aluminum collar for .5" hub axles (Ben E. said he'd do it for me) (That didn't work - James is doing it for me now).
14. Design and build a trainer to fit mag trainer (donated by Michael Hoenig).
15. Replace steel cables with Kevlar (maybe not - I think the flex of steel is good....)
16. Crotch guard / fender
17. Narrow chain stays to allow foot to clear
18. fix derailleur
19. crank hitting chain stay
20. chain stay frame flex?
21. Narrow, high density foam for seat
22. Make front quick release safety23. Change steer cable sheaves to Pete Heals idea
24. Add missing and new webs
25. Add a g-meter and quantify turning g's at flippage threshold. (add outriggers)
26. Widden the track width to 42 inches and test.
27. Solve the rear stiffness issue (If the wider track is good, then build a whole new rear triangle)
|TOTAL distance on TCR1|
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