21 Jan 2007

     First, I wanted to do a few mods on the design.  Starting at the front, I've found that unless you have at least about 16" between the BB axle and the front axle, there can be chainline issues causing shifting problems.  Also, the way the front end was built, could be simplified, so I built a python front end, but shrunk it down for a 20" wheel.  I also wanted a little extra clearance around the tire for screws/studs when in ice racer mode.  While I liked how low it was, I need to bring the rear end and king pins up a little so I could manage 20" rear wheels on it.  To the right and below are some quick mock-ups of the changes.

     The steering will be some form of USS and I will better know how jammed the cockpit is once I get the seat installed and see where a comfortable handle bar location is.  I'll also change the tie rod mounts so that they angle down and in at about 45º so the area behind the seat might be able to be used for carge or something later on.

24 Jan 2007

     So, I've been busy building for the last couple evenings and the progress is fairly good so far.  It has to be with the races only 9 days away now.  The rolling chassis is pretty much completed, and I will start in on the rear seat support, temporarily put the seat mesh on and then hit the brake caliper mounts and steering linkage.  So far it's coming along pretty much to spec.  The boom and backbone are 1½" x .063 box, and the chainstays are 2" x ½" x .063" rectangular steel.  The rear crossmember is 1¼" x .063" box steel and the seat is my standard seat but with a 45º lower seat angle like I did on the TST.  Time permitting, I'll drill a bunch of holes in the rectangular section like I did on the Python.  I used the frame jig quite a bit and it is much more versatile than I anticipated, which is a good thing, and has helped me get this far, this fast in only 3 evenings.  I also decided not to waste any time and mounted the ice tire on the front wheel seeing as how that will be my first immediate reference point for the ice races.

     The bottom picture shows the rear end.  I'll be using Delrin bushings and mounted the king pins upside down so I could keep the frame as low as possible for better CoG.  I also set the caster at 18º instead of the regular 15º because with the RWS, I want it to feel a little heavy and try to track straight a little harder than normal.  I don't know what the RWS will feel like at speed, but I don't want it to be twitchy.  I used the standard 15º king pin inclination and just kicked the tail end of the backbone up and welded the crossmembers right to the sides of it.  The steering si a bit of an unknown entity yet.  With theposition of the wheels, the length of the frame and the height of the tie rod, it'll be funky to say the least.  If I can't get a nice smooth line for a connecting link from the handlebars, I'll use twin, tensioned big gauge brake cables for steering input.  I think the brake cables will be more than strong enough because the steering input loads are far, far lighter than squeezing hard on the brakes.  Also, the nice thing about RWS and the caster angle/king pin inclination combination is that the outside corner will rise on a turn while the inside corner will drop - which effectively makes it lean into the corners a little.  Sweeeet! :)  Hopefully I get the steering linkage done tomorrow night so I can get a good look at it and then ruminate on the connecting link design for a day.

07 Feb 2007

     The trike was finished up and adapted for ice racing in Brantford.  I didn't have time to paint it, but that will be taken care of this week or early next in time for the Toronto courier ice races.  I finished up the 62/40 oval chainrings I was making and got those mounted up along with a 1/2" tubular steel front fender.  I didn't have time to fiberglass or weld up anything else, and I sort of like the look of it anyway.  Something simple to cover the top later and it's a keeper, I think.  The chainrings worked great but the chainline is too short for such a huge gear that is so close to the cluster.  If you are on the 40T and the 12T cog, it wants to upshift to the 62T because the chain hits it.  No big deal, I was planning on using a 48/38/28 triple anyway.  I made an extra brake mount for the front wheel so it would compy with the dual brake rule as an ice racer.  Once it goes back to a trike, it'll have triple brakes.

     The steering was a big pain, to be honest.  I wanted to make the seat move so that comlicates things for a USS steered bent.  Also, because it's rear wheel steer, using crossed tie rods for the rear wheels didn't work either, and using a single rod wouldn't work unless it had a big curve in it so it wouldn't hit the rear wheels during full steering lock.  A rigid rod would also complicate seat adjustment because the bars would need to move too.  In the end, I came up with a dual cable steering system that has adjustment knobs to take out all the slack, plus the steering ratio is easily adjustable to increase or decrease the steering sensitivity.  Steering sensitivity was a big concern of mine because of the oscillation issues I've seen/heard/read about with RWS trikes.  Slow steering with good "weight" was what I was aiming for when I made the caster 18º.

     I made a small U-shaped saddle that sits under the tie-rod, and I welded a tab to the center of the tie rod so a pinch bolt could secure the steering cable to the tie rod.  With cable steering, my concern was that if I didn't have all the cable routing and pivots and guides in the same place on both sides, there would be slack in one of the cables at some point.  By only having 3 pich points on a single steering cable, instead of using 4 pinch points on 2 separate cables, I simplified the system and further reduced an symmetry problems.  The end result was steering that is crisp and tight - no slop and no oscillations.  A very small amount of slack - about 1/8" appears when the steering is at full lock because of the Ackerman setup, but the outboard whell is the loaded wheel and it has a tight cable, so there is no problem there.

     The rear end consists of a pretty much standard tie rod and steering assembly, except that I welded a 1" square piece of 1/8" steel to the center of the tie rod.  I drilled a ¼" hole in the tab and another ¼" pinch bolt held the steering cable in the middle of its length.  The T-bar that supports the steering cable has its vertical piece made out of ¾" x .063" box steel, and the horizontal section is made out of ½" box.  Two small rectangular pieces of 1/8" plate steel form tabs at each end of the T.  I drilled and tapped a 6mm hole in each tab so I could use a cable adjuster (from old brake calipers) on each end.  The cable adjusters are used to take the slack out of the cable and fine tune the handlebar and tierod alignment.  Two Avid Roll-a-majigs are used to help the steering cable transition the 90º angle and make the cable more flexible when the handlebars are moved.  As the steering moves left and right, the tie rod rotates fore and aft using the rod ends as pivots and keeps the pinch bolt tab pretty much centered on the T at all times for optimum cable alignment.  With the combination of the Delrin kingpin and handlebar bushings, and the cable housings, there is a bit of drag on the steering, but not stickiness, and that drag coupled with the 18º caster gives the steering a nice "weight" without feeling too heavy or too light and twitchy.  One I get the wheels on it, I'll see what it feels like on the road.  Except at full steering lock on either side, there is zero cable slack so the steering has no response lag at all.  It worked pretty much with the same responsiveness as direct steering.

      I'm very happy with how well the steering works, but for the next delta, I will make the BB move and bring the rear end up as close as possible to the seat so I can use a simple single or double tie rod setup with something like tiller steering.  While the cable steering works very well, it was made unnecessarily complicated by my desire to have the seat AND handlebars move.  I want to make another slightly modified clone of this that is a pure ice racer.  Sort of a waste of a trike, but it can also be used as an indoor trainer when not ice racing.  It'll be shorter, wider and tilt as well :)  It should be the optimum ice racer and look sort of like a crab.  In the mean time, I'll disassemble the trike and get it painted early next week and then get it back together in time for the ice races in Toronto.

21 Feb 2007

     To the right is the finished ice racer with its nice, shiney new, high gloss powder coat.  It's very nice :)  Anyway, it was raced with the 62/40 Oval double chainring but I took it off to make the trike a little more usable and standard, and instead, replaced it with a 42/34/24 that I chopped down to 140mm from 170mm.  I also removed the friction shifters and put on Diacompe bar end shifters instead.  The trike worked very well on the ice and was very smooth. I actually thought it would run a little more twitchy, but it was fine with the steering ratio reduced.  Pictures and movies of the races are here.  Time now to put it back on the road.

09 Mar 2007

     To the right are the finished pictures of the trike.  The trike ended up a little narrower than I had planned, which is a good thing as far as getting through doorways and such is concerned.  A little extra width would make it a little more stable, but with 18º caster and a slowed down steering ratio, it still handles nicely anyway.  Due to the nice, tight king pin bushings, the steering feels a little sticky yet, but that will loosen up a little with time.  It handles and rides very smoothly and changing the steering ratio works better than I thought for calming the rear-whip tendencies of a rear wheel steer trike.  I got it going at a good clip too, but I think this is best suited as a casual tourer rather than a speed machine.  The load-balanced, dual pull rear brakes also work like a charm and those in combination with the front U-brake can really haul the trike down fast.  I'm very happy with it. Stick a fork in it, it's done :)