Chapter 3:
FIGURE
Robot Locomotion
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Illustrations of a shaft with “key” slot, “D” flat, and pin hole.
You may be lucky enough to obtain a wheel assembly with a pre-cut slot; then you can cut a corresponding slot in your shaft in which to place a “key” to lock your wheel in place. The wheel is retained on the axle with a nut and washer that allow easy removal. Go-kart and off-road suppliers may be able to furnish you with many wheel/shaft/sprocket assemblies for your robot. Another way to remove a wheel quickly for fast repairs is to have the wheel permanently mounted to the powered axle. Rather than removing the wheel, you simply flip the robot over and loosen the set screws in your pillow block bearings, remove any retaining shaft collars you may have used and the drive sprocket, and slide the complete wheel/axle assembly out. This obviously has its negative aspects, especially with a heavy robot. It also may create a bit of a problem in reassembly when you have to locate the drive sprocket and chain, and slide the shaft back through. You’ll have to locate the flattened part of the shaft you place your set-screws against or the holes through which you must insert pins, and then realign all the bearings and collars before retightening the whole thing. Protecting Your Robot’s Wheels
You might have hard rubber tires with large-diameter axles and heavy rims, but continued pounding by another robot can take its toll on your machine’s wheels in nothing flat. An easy way to protect the tires is to have them enclosed within a heavy part of the body’s shell, or you can mount a rim around the outside at the tire’s most vulnerable parts. You must make this outer shell structure or rim strong so that denting caused by a hazard or opponent’s weapon will not cause any part of the metal structure to come in contact with the tire, in which case it could act like a brake or cut the tire. There are more ways to provide power to wheels than we could ever print in this book. Belt drives have been used successfully, as well as friction drives on the wheels. Canted wheel drives have been used on several robots to provide a wide wheelbase in a smaller-sized robot. Your best approach is to look at what’s been done, what bot designs have consistently won over a period of time, and what designs seem to have been problematic. As we mentioned in the beginning, we will never attempt to tell you what is the best design—with a bit of experimenting, you might be able to produce something better than any of today’s champion bots.
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