Page 306 - Robot Builder's Bonanza

MOUNTING WHEELS TO R/C SERVOS 275

Figure 24- 9 Most any kind of wheel
can be converted for use with an R/C
servo by attaching a servo horn to the
side of the wheel. If your servo didn’t
come with an assortment of horns, you
can purchase them separately.

Servos differ in the type of spline used on their output gear. The three most common spline types
G are noted simply by the servo manufacturer that popularized them: Hitec, Futaba, and
Airtronics. If you are purchasing wheels for your servos, make sure the wheels use a matching
hub spline. Wheels made for standard- size Futaba servos will also work on any other brand
that uses the same Futaba- style spline, such as GWS.

MAKING YOUR OWN WHEELS FOR SERVOS
The general approach for attaching wheels to servos is to use the round servo horn that
comes with the servo and secure it to the wheel using screws or glue (see Figure 24- 9). The
underside of the horn fits snugly over the output shaft of the servo. Here are some ideas:

Lightweight foam tires, popular for model airplanes, can be glued or screwed to the servo
horn. Popular brands are Dave Brown and Du- Bro, and these can be found at most any
well- stocked R/C hobby store. The tires are available in a variety of diameters, with the
2″, 2- 1/2″, and 3″ diameters the best for small bots.
Large LEGO “balloon” tires have a recessed hub that exactly fits the small, round servo
horn included with Hitec and many other servos. You can simply glue the horn into the
rim of the tire.
A gear glued or screwed into the servo horn can be used as an ersatz wheel or as a gear
that drives a wheel mounted on another shaft.
Homemade O- ring wheels can be constructed out of two plastic discs, cut to any diame-
ter you like— though about 3- 1/2″ is a practical maximum. The O- ring is the rubber tire
of the wheel. At the center of the discs, mount a large, round servo horn, then fasten
the pieces together using miniature machine screws and nuts.
Pulley horns look like three discs cemented together with a space in between. You can
turn the pulley horn into a unique wheel by adding a pair of rubber O- rings as tire
treads.
Urethane skateboard/inline roller- skate wheels make for incredibly “grippy” wheels for
robots. The trick, if it can be called that, is to find metal or plastic discs that just fit into
the hub of the wheel. Most skate and inline blade wheels use metric sizes, with a hub
diameter of 22 mm. A 0.625″-diameter fender washer fits into the bore of the wheel
but is (usually) large enough to stop against the ridge that’s molded into the center of the
wheel. Hold all the pieces together with a 4- 40 machine screw that goes from the out-
side of the wheel and directly into the servo motor output shaft.

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