N E of the most important considerations in the design of your robot is locomotion. You can use a propeller, or even a jet engine, to “blow” your machine along, but these sorts of propellants are not allowed in most competitions and would prove to be quite ineffective anyway. Moving parts that actually touch the floor are the preferred method of providing controlled movement to your robot, with wheels being the most chosen method. The following are some definitions used in this book: ■
Speed reduction Transforming high RPM and low torque power into low RPM, high torque power.
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Speed reducer
The device that does the speed reduction.
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Gear reduction
Speed reduction using gears.
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Power transmission Every device and component that transmits power from the motor to the wheels (including the speed reducer).
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Transmission A speed reducer with more than one reduction ratio. Note that a transmission is only one component in the “power transmission.” The two terms are not interchangeable.
The purpose of the power transmission is to transmit the rotational energy from the motors to the wheels of the robot, and many different ways can be employed to do this. The simplest way is to use a direct drive method. With this method, the wheel’s hub, or axle, is directly connected to the motor—either directly on the output shaft of the motor or the output shaft of a gearmotor. A gearmotor is a single unit with a gearbox and a motor combined into one convenient package. The gearbox is used to decrease the rotational speed of the motor to a more usable output shaft speed. Many electric motors’ rotational speeds range between 3000 to 20000 RPM. This speed is too fast for directly driving a robot’s wheels—unless you want your robot to move at warp speed. The gearbox also increases the actual torque of the electric motor to a much higher value on the output shaft. The higher torque will give your robot more pushing power. Although many robot builders use the gearmotor approach, some have used non-gearmotors to power the wheels directly. For example, the middle and heavyweight entries from team Whyachi used direct-drive Magmotors in their robots. 104