I’m working on designing a ball-shifting gearbox as a CAD exercise. I’m going to use this pancake shifter from VEX. My best idea as to how to make it attach to the ball-shifting rod is to have the rod female-tapped on the end and have it screw on, but my concern is that it might introduce difficulty in switching parts out or in assembly.
I’ve checked the CAD of some COTS gearboxes and what they do is some weird plastic coupler which isn’t sold independently. I’d prefer not to use this if possible if I can’t get my hands on it.
The coupler used in COTS gearboxes is soldseparately. For these kinds of things, go to the page for the full gearbox and look for the links at the bottom in “kit contents”.
The reason vex does a “weird plastic coupler” is that there’s a bearing inside, so that the gearbox doesn’t rotate the pancake cylinder’s shaft and wear it out.
As mentioned above, most of these gearboxes, both ball and dog shifting, use a part that attaches to the pneumatic and has a bearing in it to allow the shifting shaft to rotate. You’re right that these can be a bit of a pain to assemble especially when designs pack things as close together as possible, vex’s two part design does make this easier.
Way back in 2011 192 actually made a gearbox that didn’t have this bearing and we just spun the rod of the standard cylinder we were using. To take this approach we had a part that the rod threaded into but we also had to drill and pin through it so it wouldn’t unthread.
EDIT: Sorry, didn’t make clear that I’m definitely not recommending going without a bearing. It was a quick fix because our bearing design was to big and we didn’t have time to redesign it.
I would recommend against doing this because the pistons are not designed to spin. 192 may have gotten away with it in 2011, but I know of others who have done this back in the early days before readily available COTS shifter components and ended up burning up piston seals.
973 had a nicely packaged shifter on one of their off-season robots this year that made use of a 3D printed part to capture the bearing. This enabled them to have a clean flipped cylinder design that interfaced nicely into the VP shifter selector shaft.
If you have 1/2 hex stock, a harbour freight 8x10 lathe, appropriate taps/dies, as much patience as my students, and a willingness to use a lot of blue loctite on assembly - you can make the adapter my students came up with instead of buying the Vex kit.
I posted a rough drawing to CD-Media, it should show up by tomorrow and I’ll edit this post to link to it.
My choice would be to buy it, but I am not as patient as my students.