Step 1: Go get stuff
(x1) continuous rotation servo modified for direct drive**
(x1) 18" aluminum ruler (or longer)
(x2) small plastic container
(x2) 2" - 3" fixed casters
(x1) bic Classic pen
(x10) small nuts and bolts
(x4) small washers
(x1) 2" - 3" metal standoff
(x4) zip ties
(x1) DPDT lever switch
(x1) 4 x AA battery holder
(x4) AA batteries
(x1) red and black wire
(x1) electrical tape
**Learn how to modify a servo motor for direct drive at this page.
Step 2: Cut the ruler
(The convenient thing about cutting a ruler is that it comes pre-measured.)
Step 3: Fold a notch
Place the ruler in a bench vice so that the bottom of the cuts are level with the top of the vice.
Hammer the section between the two cuts flat such that it is made perpendicular.
This will be your motor mount.
Step 4: Drill holes
Remove the motor and drill through your marks with an 1/8" drill bit.
Step 5: Drill more holes
(Obviously, on the piece that you have already worked on, the hole has to be drilled on the opposite side of the motor mount)
Step 6: Even more holes
Use your servo horn as a guide to both mark and drill 1/8" holes through the section of ruler that does not have the motor mount.
These holes should be drilled roughly 1/2" in from the edge of the ruler.
It is preferential if you simultaneously drill the servo horn, as to ensure identical sized holes.
Step 7: A few last holes.
Drill a 3/16" hole upon the section with the servo horn mount that is roughly 5" from the edge with the servo horn mount and close to the edge of the ruler. Drill a second larger 1/4" hole that is 4" from the servo horn mount and centered upon the ruler.
Congratulations! You are finally done modding the ruler.
Step 8: Mount the motor
Attach that servo motor's horn, if you have not done so already. Use nuts and bolts to attach the other section of the ruler to the servo horn. Again, the screw heads should be facing inward towards the other set to ensure a low profile.
Step 9: Modify your comb
When you are done removing teeth, sand that section of the comb smooth.
Lastly, drill an 1/8" hole on the opposite edge.
Step 10: Attach your comb
Once it is passed through, place 2 - 4 washers on it. The point of these washers is to push the comb towards the other section of ruler (once mounted).
Next, pass the screw through the middle hole, in the section of ruler with the motor, from the inside out. Use your bolt to securely fasten it in place.
Step 11: Wire up the switch
Solder a red wire from the bottom left corner pin to the top right. Solder a black wire from the bottom right, to the top left.
While you're at it solder the red wire from your motor to the pin on the bottom of the switch with the red wire and the black wire from the motor to the pin on the bottom with the black wire.
Lastly, solder a long red wire to the middle pin on the side with the red motor wire and a long black wire to the middle pin on the side with the black motor wire.
If you are confused, just look at the wiring diagram below.
Step 12: Standoff
The comb will rest atop the standoff.
Step 13: Spacers
With a razor blade, cut down on the tube creating two 1" sections.
Take the two sections and cut them in half, creating four 1/2" sections.
Step 14: Remove the wheels
Set the wheels aside for some later project.
Step 15: Pivots
Use the holes in the caster as guides for drilling 1/8" holes in the lid of the container.
Zip tie the caster frame in place to create pivots.
Step 16: Power box
Place the battery holder inside and pass the power wires through the hole.
(I know that it shows batteries in the holder, but I recommend not inserting batteries before you solder.)
Step 17: Put it all together
Basically, the ruler should have a pen spacer on each side to hold it in place. If it seems loose or tipsy, insert metal washers between the spacer and the ruler until it is not.
Step 18: Power connections
Solder the red wire from the switch to the red wire from the battery holder and cover it with electrical tape.
Solder the black wire from the switch to the black wire from the battery holder and cover it with tape as well.
Step 19: How it works
So, as the motor turns, the comb slides to one end and hits the switch. This then causes the comb to slide back to the other end, to hit the switch once more. Rinse. Repeat.
If you find that the motor does not reverse when the switch is pressed and the bot folds itself up into an ugly mess, first REMOVE THE BATTERY! Once you have done that, rotate the switch 180 degrees. Now put the battery back in. When the switch is pressed, it should reverse direction.