At some point at our Personal Photonics Project at the Media Comuting Group Aachen, funded by the german ministry of education and science for developing a haptic toolkit for helping visual impaired people, a paraplegic guy approched us who controls his wheelchair (and other things) with a ring of big buttons behind his head. Problem is that these buttons break easily, are expensive and not reliable. Question was if there might be an cheaper maker solution. Of course, that was not the main focus of the work, but still sort of fits into the idea of the project (and seems to be something easily achievable and useful). Of course, it turned out that we needed a bit more iterations, but at least now we have a version which seems to work as intended and is easily reproducable.

Step 1: First: Some Ideas Which Didn't Work Well

So the basic idea was translating a normal small button into a bigger one. With using a beared hinge at one side we wanted to have a lever and reducing the danger that the button get stuck (which is dangerous, e.g. if the wheelchair drives with full speed). Additionally we intended to use two buttons instead of one, if one of them got stuck, nothing dangerous will happen. Functionality of booth buttons can be checked by opening the hinge. Furthermore, we wanted to use a relative robust button, which turned out to be to strong for stearing the wheelchair (but might be good for gaming). In the first iteration button size was to small and height needs to be reduced, as well as getting rid of the second button inside and using a standard subminiature snap action switch (without metal lever, this part also tend to get stuck).

Reducing heigth caused another challenge: The wall size around the bearing was to small, therefore we got away from bearings and used a 3mm teflon tube (from a 3D printer) as hinge.

For historic reasons (and since they might be useful for other purposes), the old design files are still included in this step.

Step 2: Printing and Electronics

For the final version (well, until the next round of feedback comes in), you have first to decide if you want the harder version for games or softer for stearing, both of them needs different kind of buttons inside, either a snap action switch or the mentioned button before. For other kind of buttons you might to change the OpenScad files. The designs can than be printed without support material on a normal FDM 3D-printer.

Afterwards, test if the button fits or if the design needs to be scaled. Then, solder a wire with a 3.5mm Mono headphone jack on the botton, the wire should go through the hole perpendicular to the hinge into the housing. The snap action switch is secured with two 2mm screws (rougly 2cm long) through the holes on the side of the bottom, while the other button is just glued with epoxy on the ground of the bottom halve. Additionally, the wire is secured within the housing with a drop of Epoxy.

Afterwards, add the the lid and check if the button works when pressed.

Step 3: Hinge

In the last step, insert a 3mm inner diameter teflon tube inside the bottom hinge part, then insert a 3cm 3mm allen screw from one side of the top part (round hole, the other 6edge gap is for the corresponding nut). Washers on each side of the hinge helps reducing the friction. Already done and Ready to use!

Minor side notes: The Button can be either screwed on with holes in the bottom (but with a very flat screwhead), most of the time velcro is glued at the bottom. Furthermore, a small pillow can be glued on top to make it more comfortable to use.