5 Jan 2016

5th January 2016 The Trykit resurrection.

Tuesday 5th 25F, -4C, windy but clear. Snow showers possible on top of a strong, easterly wind.

With my replacement levers having arrived and an unfinished Shim[sram]ergo system still incomplete I will have to get busy. It is still very cold and won't be any warmer the shed. The wind is still gusting to 12m/s or over 25mph so wind chill at -4C puts is near -20C equivalent.

I always prefer to work outside with the trike up on the workstand. There is not enough room in the shed to work all around a trike.

The image shows the pulleys now pivoted at the 2nd [output] pulley. The dimensions shown provide a perfect match of 1:1.38 between the Ergo 11 speed levers and the XT11 MTB rear derailleur.

Even with the cable clamps on the swinging arm the indexing was perfect. The Ergo lever movements had been lighter than with a Campagnolo Athena 11 speed rear changer. Tragically my lack of maintenance and constant gear changing had caused the right hand Chorus lever to give up. I believe a small pawl had broken off. One which usually pushes the ratchet wheels around to select gears by gathering and releasing cable in indexed steps. I have not attempted to dismantle the broken lever despite there being excellent videos online. Fortunately I was able to ride my back-up Higgins trike or I would have been without transport.

In the meantime, I have been "thinking furiously" about how to overcome the sharp cable bends I was forced to use with the original cable clamps. These damaged the cable and made it impossible to withdraw the inner from the final RD loop. It was far too crude a system for my tastes. So now I am hoping the rubber "pulleys" will solve the cable problems by providing enough friction to avoid cable slippage. Hopefully without any need for cable clamping at all. If the cable does slip then I shall have to add a non-damaging clamp to the swinging arm. Since the cable will pass straight through the clamp there will be only a little cable flexing at the anchor.

The pulleys are thinner than the original clamp bolt heads. So the pull-ratio changing mechanism is narrowed quite considerably. It could be made thinner still by cutting a single piece of aluminium to support the asymmetrically arranged pulleys. The disadvantage is that adjustability is lost unless I slot the pulley fixing holes. Otherwise the geometry would have to be designed for a specific match between a chosen lever and a particular rear derailleur. I have no need of adjustability myself because my choices are already made. Though it is nice to have some leeway should it be needed in practice. It is quite possible that the swinging arm geometry will affect the cable pull per click at the extremes of arm movement. This could be compensated for by slightly altering the relative positions of the pulleys. If the indexing runs short of movement on the lowest gears then the ratio could be slightly increased.

The rubber pulleys proved to be too soft in practice. They offered plenty of cable grip with good indexing but the cable was soon dragged over the grommet's rim sideways by the offset cable pull. The only way to get a straight pull would be to drill holes right through the seat tube down by the bottom bracket. You may rest assured that my near-obsessive desire to have the Shimergo system working does not extend to that level.  I have gone back to using the original cable clamps for the moment despite the sharp bends. This problem could be overcome by using turned alloy pulleys with deep rim grooves. In the image it looks as if I have reversed the pivot clamp but it makes little real difference.

There is a serious problem with the rear derailleur cable loop being blocked by the trike's rear axle loop. After much fiddling I was able to find a point where rotating the "Direct link" allowed the cable to reach the changer. It was just bad luck that Shimano had made the cable entry at such an extreme outward angle to the vertical. How this would affect an MTB is difficult to say but it must surely make the rear cable loop extremely vulnerable to catching on branches. A mere 1/4" shorter "Direct link" would have helped the cable to clear the axle loop completely. The XT11 changer wouldn't fit directly on the Trykit gear hanger without the supplied link.

It took ages to get the tape off the handlebars where it had welded itself to the silicone shock absorbing strips. The black finished bars have suffered considerable cosmetic damage where I had the tri/bar extensions clamped. I may have to tape the bars right to the center. After weak morning sunshine it clouded over, as if about to snow, but hasn't so far. It didn't feel too cold in my big duvet jacket as it slowly warmed up to -1C, 30F.

I had to go back to the thinner central spacer on the Trykit 2WD because the freewheeling friction was far too high with the original spacer. It was very hard work turning the pedals in top gear even without the back wheels because there was so much drag! It is much better now with the thin spacer in place. I just have to re-tape the bars now and I will be mobile again.

Click on any image for an enlargement.

No comments:

Post a Comment