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Philadelphia Robotics Group Message Board › Re-working my encoder wheel

Re-working my encoder wheel

Bob A.
user 69549842
Medford, NJ
Post #: 5
Thanks for the comments last night about possible problems with my encoder. This evening I pulled one wheel apart and started building a new reflector for the inside surface.

This started with a thin piece of cardboard, probably from a box of tissues or cereal. I contact-glued aluminum foil to it and let it dry an hour. While drying, I printed a new pattern and cut out the white portions, or at least enough to expose the whole wheel, then touched up all the edges of the paper with black marker and then glued it to the foil.

The aluminum foil should be a *tad* more reflective than the white paper. The previous pattern's black printed areas had faded quite a bit too, so hopefully this makes things better and then I can get back to the electronic portion.

I'll post some pictures once it's done.
Bob A.
user 69549842
Medford, NJ
Post #: 6
it worked!!!

As I rotate the robot's wheel, the output swings from almost zero to almost five volts. I removed the cardboard shield and it still worked perfectly.

The IR reflector assembly is a TRW OPB 709 that I picked up someplace in Silicon Valley during a business trip.

Now to build another of these and finally make some progress on the PID control loop.

Earl M.
Abington, PA
Post #: 20
Glad the foil reflectors are working out.

I wonder if cutting out a circle from an aluminum beverage can, spinning it against a backing plate while polishing it with steel wool, would give you a smoother reflective surface.

However, if the foil is working, move on.
Bob A.
user 69549842
Medford, NJ
Post #: 7
I do have a nice assortment of flat aluminum pieces, courtesy of another hobby, but was trying to use stuff that the average person might have around. Aluminum foil seemed so low-tech that it was perfect.

Had to add a 74LS14 Schmitt trigger and a pull-down resistor to clean up the analog edges, then the Arduino started getting perfect detection of the transitions.

There hasn't been much time to tweak the PID constants yet, so the servo speeds are not adjusting properly, but this is the fun part :)
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