Robot Bumpers From An Aluminum Door Seal

I wanted rubber bumpers for my robot that would both protect the furniture, and let it know when it had hit something. I looked into a number of options. The conductive foam and piezeo-electric film mentioned in Robot Builders Bonanza seemed promising. However, the film is rather expensive for a robot of this size ( I ended up needing about 6 linear feet to go around the bot). The conductive foam can be had cheaply, but still needed a way to mount it.

Another option is Controflex Ribbon Switches, still carried at Herback and Rademan. These, however, are really expensive, at $43.50 for 5 feet, and you still need ends.

On a trip to my local hardware store, I came across a piece of aluminum channel with a rubber gasket in it. It's sold as seal to put under a door. It actually has two pieces, as in the first two pictures below. One piece is an L shape, that screws to one side of the door and holds the rubber underneath. The second piece slide into the first, locks in place, and secures to the other side of the door. The first two pictures give an example of the stock, should you be looking for it. A 3 foot section was under $12.

These not only seemed like a perfect bumper, but it looked easy enough to turn into a bumper switch. My initial idea was to use some sort of thick foam tape with a metal backing attached to the inside of the rubber. When the rubber was deflected, the tape and foil would make contact with the aluminum frame, completing a switch.

However, thick foam tape is surprisingly hard to come by, and expensive. On the other hand, foam weatherstripping is cheap and plentiful. I used 3/4 inch wide by 1/4 inch thick foam weather stripping. For the conductive layer, I coated the non-sticky side of the weatherstripping with glue, pushed a wire into the glue, and covered it with oven grade aluminum foil (yup, good old Reynolds Wrap.)

Incidentally, I did try foil tape. However, the glue on the foil tape itself is not conductive. It turned out to be very difficult to attach a wire in such a way that it would make contact. By putting glue on the foam first and setting the wire in that, there was nothing between the wire and foil.

I took some pictures below of the finished product (and some of the leftover stock to give an idea of what it looks like). I have some pictures of the foam/foil being made in my 35mm camera, which should be developed in a few days.

While the aluminum framing came out fairly well, I'm not entirely happy with how the corners came out on the rubber. The rubber is sold as a replacement for about $2.50 a 3 foot section, so if I ever get ambitious it isn't a big deal to replace. For now I want to move on with my bot.

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