2017-02-28, 12:32
Whilst I've been back home on the island and had my own workshop I thought I would make the original shifter electronic. I didn't wan't to try and fit a potentiometer into the shifter itself as combining two parts that could need replacing isn't ideal. I also had a load of reasonable quality audio slide pots I got for free. Would rather use them than a tiny pot squeezed into the shifter. I'd considered buttons but decided waterproofing them could be a challenge and I like the robustness of a standard shifter.
Next challenge was applying a pull to the cable to simulate the derailleur and so the shifter works correctly. Taking up 27mm of pull with a spring without a massive change in tension wasn't easy. I eventually choose a chain tensioner spring off an old derailleur. Its got a good length spring, the change in tension is noticeable but not a problem.
![[Image: G3F0hS.jpg]](http://imageshack.com/a/img924/3775/G3F0hS.jpg)
A radius of 17mm gives a 90° rotation on the derailleur spring.
The slide pot has a length of 60mm which is a common size. I was going to amplify the cable pull to make full use of this. However it was far simpler to make a cable grip and fit the pot in parallel to the cable. With a total of 1023 values for the full 60mm length it still works out at 60 between each shifter position when using just half the length. Its also nice to have spare room at each end.
![[Image: 7PYOfu.jpg]](http://imageshack.com/a/img924/4597/7PYOfu.jpg)
The cable grip which fits the potentiometer on right of pic.
The code writing for it required a little bit of thought. I wanted to include some deadband as the shifter overshoots a bit although once shifted it settles to a pretty consistent value. Too much deadband made the range per cadence settings so small it would sometimes get missed. A deadband of 10 seems to be about right with a range of 60 between each setting.
![[Image: x92ffm.jpg]](http://imageshack.com/a/img923/6228/x92ffm.jpg)
Its big and heavy for what it does but should be reliable and easy to fix. As it can be used with any type of shifter that pulls a cable making any bike automatic is a bit easier, could be useful. Its an experiment to see if there is a use for such a thing.
Next challenge was applying a pull to the cable to simulate the derailleur and so the shifter works correctly. Taking up 27mm of pull with a spring without a massive change in tension wasn't easy. I eventually choose a chain tensioner spring off an old derailleur. Its got a good length spring, the change in tension is noticeable but not a problem.
A radius of 17mm gives a 90° rotation on the derailleur spring.The slide pot has a length of 60mm which is a common size. I was going to amplify the cable pull to make full use of this. However it was far simpler to make a cable grip and fit the pot in parallel to the cable. With a total of 1023 values for the full 60mm length it still works out at 60 between each shifter position when using just half the length. Its also nice to have spare room at each end.
The cable grip which fits the potentiometer on right of pic.The code writing for it required a little bit of thought. I wanted to include some deadband as the shifter overshoots a bit although once shifted it settles to a pretty consistent value. Too much deadband made the range per cadence settings so small it would sometimes get missed. A deadband of 10 seems to be about right with a range of 60 between each setting.
Its big and heavy for what it does but should be reliable and easy to fix. As it can be used with any type of shifter that pulls a cable making any bike automatic is a bit easier, could be useful. Its an experiment to see if there is a use for such a thing.
- Oran