Page 310 - Robot Builder's Bonanza

USING RIGID AND FLEXIBLE COUPLERS 279

Figure 24- 12 A three- piece jaw
coupler uses two metal or plastic “jaws”
that connect to the driveshafts and a
softer (often rubber) inner piece that
provides the flexibility.

are the “jaws.” A third, rubberized piece, the spider, fits between the jaws and acts as a flex-
ible cushion.
One advantage of three- piece couplers is that because each piece of the jaw is sold sepa-
rately, you can readily “mix and match” shaft sizes. For example, you can purchase one jaw
for a 1/4″ shaft and another for a 3/8″ shaft. Both jaws must have the same outside diameter.

MAKING YOUR OWN RIGID COUPLERS
To save money, you can make your own rigid couplers using metal tubing, metal or plastic
standoffs, or threaded couplers.
Couplers from Tubing
You can get brass, steel, and aluminum tubing of various diameters at hobby stores; larger
aluminum tubing can be found at home improvement outlets. Most tubing is sold by its inner
diameter—1/8″ tubing measures an eighth of an inch inside, for example. The thickness of
the tubing determines its outside diameter. Get tubing that fits over the motor or wheel shaft
you’re attaching to.
When matching up tubing, note its I.D. (inside diameter). Tubing at the hobby store is meant to
G fit into the next size larger, as in a folding telescope. You can use this feature to match one shaft
diameter to another. Typical thickness of the tubing is between 0.014″ and 0.049″, though this
varies somewhat by brand.

For lightweight robots with small motors, look at 1/8″ or 3/16″ I.D. If possible, bring your
motor or wheel (or just the shaft) to the store with you so you can test the pieces for proper fit.
To use, cut the tubing to length. Use a tubing cutter instead of a saw. You can then secure
the tubing to the shaft in several different ways, including the following:

• Crimp it on with an appropriately sized metal collar. The collar comes with a setscrew.
Carefully tighten the setscrew over the tubing (see Figure 24- 13). This type of metal collar
is available at any R/C hobby store and often goes by the name Dura Collar. If you can’t
find a collar just the right size for the tubing, you may need to select the next size smaller,
then drill it out. The collar is typically plated brass, so it’s not as hard to drill as it may look.

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