This is a very home-brew effort at converting a couple of Ultimarc J-sticks to be rotary as well. It works well for me, could be improved I'm sure.
Basically I cut 2 small pieces of aluminium (type of stuff you might get covering a drive bay on an external hard drive enclosure). About 2cm by 1cm. The J-stick has a grove on the 'top' of the base, like a screwdriver head, as does top of the rotary encoder. So I just glued this small piece of aluminium into the grove of both.....
The silver bit in the middle is the thin piece of aluminium (the j-stick is totally unaltered - just a blob of glue). It also happened to fit snugly in the grove on the shaft of the encoder (my luck was in). One 5 min session of perma-bond later, and hey presto.
The rotary encoders came out of an old audio mixing desk. (I've got 2 j-sticks done this way). The black shaft on them spins in the base, so for testing I simply took 2 paper clips and un-folded them a bit, I hooked one under one of the screws on the j-stick base, pointing vertically (parallel to the encoder shaft) and left it with a hoop at the end (ie left one bend in the paper clip). The other paper clip I straightened (anything straight would do) and glued to the bottom of the encoder base, protruding through the hoop in the paper-clip that is vertical. So when you spin the jstick shaft, the whole encoder begins to spin, but the straight paperclip pushes against the hooped vertical one, stopping the encoder base spinning, so just the encoder shaft spins....
Hope that made sense.... I tested it through an optipac in windows and could move the mouse up/down across the screen no problem.
The encoders themselves may be harder to find. These particular ones are made by http://www.bourns.com
(look at Rotary encoders -> Contacting in the left hand menu). It’s a ECW model. This means that mine 'click' into position rather than spin freely. These happen to have 24 positions in 360. You can feel the click as you spin the joystick, but it does not resist much at all. I have no idea who sells them or how much I'm afraid.
A pdf of the encoder specs : http://www.bourns.com/pdfs/ECW1J.pdf
This could be improved by having encoders that either have no clicks at all, or maybe only 8 (more suitable for some games?). Should be nice for those extra few games though.... (If I ever build a cab...)
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