Page 312 - Robot Builder's Bonanza

USING RIGID AND FLEXIBLE COUPLERS 281

To make shaft couplers, you should have a vise and a drill press in order to make
accurate holes. You also need a tap set with drill bits. The bits are already correctly sized
for the taps.

Nylon can’t hold a thread as well as aluminum or steel. If you go with a nylon standoff, use it
G only with shafts that have a flatted side to them. Round shafts require more pressure to keep
them from turning, but this added pressure of the setscrew against the nylon just strips out the
threads.

1. Secure the standoff or coupler into the vise. Make it nice and snug.
2. Use a center punch to mark where you will be drilling. You want two holes, no closer
than about 1/4″ from the ends. The punch makes a mark in the plastic or metal that
serves as a pilot for keeping the bit on track.
3. For metal standoffs and couplers, apply some light machine or cutting oil on the mark.
Slowly drill the holes for the setscrews all the way through one side of the standoff or
coupler. Don’t drill through to the other side unless you want to put setscrews on that
side as well.
4. Turn the standoff or coupler on end and tighten in the vise. Change the drill bit to the
size of the shaft you’re using. For example, if the shaft is 1/8″ in diameter, use a 1/8″
drill bit.
5. Drill halfway down the length of the standoff or coupler, then turn it upside down. Drill
through the second half.
6. Now to tap the holes for the setscrews. Change the bit (if needed) to the correct size
for the setscrew you wish to use. See Appendix C, “Mechanical Reference,” for a
handy list of drill bits and tap sizes for making different kinds of holes.
7. Put a drop or two of machine or cutting oil into the holes you’ve drilled (metal standoff
or coupler only), then carefully tap them to make threads. You can skip the cutting oil
when tapping into plastic.

G I’m not going to give a lot of detailed explanation about how to use taps to thread a hole, as
this information is everywhere on the Internet. Do a quick Web search for phrases like how to
drill and tap.

MAKING YOUR OWN FLEXIBLE COUPLERS
For many desktop robotics jobs, flexible plastic rubber tubing will work just dandy as a coupler.
Select the rubber tubing so that it is just slightly smaller than the motor shaft and wheel axle
you are using, and press it on for a good fit. If the motors develop too much torque for the
press- fit to hold, use small worm- gear clamps to hold the tubing in place. You can get these
worm- gear clamps at any hardware store.
See Figure 24- 15 for one example. The wheel is held in place with a pillow block, which
is merely a piece of wood, plastic, or metal with a hole in it that’s fastened to the base of the
bot. Use a long machine screw as the wheel axle; hold the wheel- axle combo in the pillow
block with a pair of nylon insert locking nuts, as shown. Plastic tubing is available at hardware
and home improvement outlets, as well as many hobby stores and pet stores that sell fish
aquarium supplies.

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