Crash! Yep, I was experimenting with the slight oscillation I thought I felt yesterday trying to induce a tip and over she went! I landed on my side and the trike landed on me. Everyone was fine though including the bike.
This oscillation is nasty and has me a little concerned. It seems to happen with some frequency of peddling cadence and body rocking from side to side. I had taken the elastomers off when it happened and they tend to deaden this oscillation quite a bit. When you start to feel it you simply stop peddling or change your cadence and it goes away - but still, I don't like it. The tip was initially caused by the oscillation, but it was a sharp turn that caused the inside rear wheel to lift and go over. I'm not too concerned about the tip, as it was a VERY sharp turn at fairly high rate of speed- something that I would not normally do in average daily riding and I've flipped my Kett delta trike over with much less of a turn.
I spent some time adding various cushion sizes to the seat to raise and lower my center of gravity with regard to the pivot line, and nothing made any difference at all. I went back to the prototype which features a slightly different geometry (seat angle and pivot line) and it was the same story there. I could induce this oscillation with any configuration.
From my experience with both the prototype and the TCR1, I am becoming more convinced that free-pivoting lean-steer delta trikes are unstable in some situations - However, and I've said this before and I'll say it now louder - EVERYTHING changes when you add steering linkage to it - I'll call it "controlled pivoting". Steering linkage prevents the trike from pivoting when you are not steering - in a sense, it 'locks' the pivot when not being used. Then it becomes the ultimate human powered vehicle sporting the best features of all bikes. The stability of a delta trike, the maneuverability of a tadpole trike combined with the feel of a two wheeler banking in turns. Most importantly, because the front drive wheel is locked into place, it benefits from the mechanical efficiency of a road bike with a short, efficient drivetrain.
The prototype used two levers with cables and pulleys to lock out the steering, but I had some issues with cables snapping off pulleys, so I'm looking into some other solutions. Possibly brake cables and a steering bar - that's next on the agenda.
Above: me cruising.
Above: My SolidWorks guru Ben Eadie enjoying a ride and nut roasting.
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