Page 311 - Robot Builder's Bonanza

280 MOUNTING MOTORS AND WHEELS

Collar with
setscrew

Motor shaft Wheel

Thin wall aluminum Figure 24- 14 Metal collars may be
or brass tubing
(sized to fit into wheel hub) used on wheels with an outsized hub (the
hub protrudes from the wheel, giving more
Figure 24- 13 Thin tubing doesn’t have enough “bite” for a surface area to the shaft). Place the collar
setscrew. But you can use a metal collar around the tubing to around the hub of the wheel. The
provide compression against a solid motor shaft. Tighten the compression tightens the hub around
setscrew in the collar for a solid fit. the motor shaft.

• Use large wire crimper pliers to squeeze the tubing around the shaft. This works only for
thin- walled tubing and when working with smaller motors that don’t develop a lot of torque.

When using the crimp- on metal collar trick, you can help cinch up the fit by drilling a small
(1/16″) hole in the tubing where the setscrew for the collar will go. This works well when using
thicker- walled tubing. When assembling the collar over the tubing, carefully line up the hole
with the setscrew, then tighten the screw.

Don’t forget that some wheels have outsized hubs, like the one in Figure 24- 14. You may not
G even need to use tubing to make a coupler. Just attach the collar around the existing hub of the
wheel, and tighten the set screw. With plastic wheels the hub will deform, cinching around the
shaft for a fairly tight fit.

Couplings from Standoffs and Threaded Couplers
Commercially available rigid couplers often use setscrews to hold the coupler to the shaft.
Thin- wall tubing is too thin for a setscrew. You need a thicker- walled coupler.
There are two ready- made sources of short metal and plastic begging to be turned into
shaft couplers: standoffs and something called threaded couplers.

Standoffs are commonly used in electronics projects to keep two circuit boards or other
pieces separate from one another. I regularly use metal and plastic standoffs to add
additional “decks” to my robots. The decks are like tiers in a wedding cake.The stand-
offs are typically 1″ or longer and are made of nylon, steel, or aluminum. I like working
with aluminum over steel, as aluminum is easier to drill and cut. You can get either the
threaded or the nonthreaded kind, but the unthreaded kind is easier to work with.
Threaded couplers are just like standoffs but are almost always made of heavier steel. You
get them at the local hardware or home improvement store. They come in thread sizes
from 6- 32 to 5/16″ and larger. The 6- 32 thread size is about right for 1/8″ shafts.

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