Robotics Universe

Motors are rated by their voltage, current draw, output speed, and torque.

Operating Voltage

Operating voltage specifies the nominal (normal) voltage the manufacturer recommends for the motor. Most small DC motors are designed for 1.5 to 12 volt operation, with the majority in the 3-6 volt range. Larger DC motors designed for heavy-duty applications usually require 12 to 24 volts, with some needing upwards of 90 volts. Often, but not always, the higher the voltage, the more powerful the motor (this does not apply to stepper motors, where very low voltages — on the order of just a few volts — are common for heavy-duty motors). Most motors can be run at operating voltages higher or lower than the specified rating. 

• Lower voltages reduce torque and speed.
• Higher voltages increase torque and speed.

 (Note: For stepper motors, speed is not greatly altered by changing the voltage.)

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Electric motors are used to “actuate” something in your robot: its wheels, legs, tracks, arms, fingers, sensor turrets, or weapon systems. There are literally dozens of types of electric motors (and many more if you count gasoline and other fueled engines), but for amateur robotics, the choice comes down to these three:

• In a continuous DC motor, application of power causes the shaft to rotate continually. The shaft stops only when the power is removed, of if the motor is stalled because it can no longer drive the load attached to it.
• In a stepping motor, applying power causes the shaft to rotate a few degrees, then stop. Continuous rotation of the shaft requires that the power be pulsed to the motor. As with continuous DC motors, there are sub-types of stepping motors. Permanent magnet steppers are the ones you’ll likely encounter, and they are also the easiest to use.
• A special “subset” of continuous motors is the servo motor, which in typical cases combines a continuous DC motor with a “feedback loop” to ensure accurate positioning. There are many, many types of servo motors; a common form is the kind used in model and hobby radio-controlled cars and planes.

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Ready-made toys are those that come pre-assembled, but that can be taken apart for useful parts. Good examples are Bio-Bugs (Wowwee), Furby (Tiger Electronics), and various motorized Tonka (and similar) tractors and trucks.

These and other toys like them can often be found on the clearance aisles, at garage sales, and even in thrift stores. At full price many of these toys don’t have enough useful parts in them to justify their cost, so always strive to purchase them used or at a discount. 

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Once you know the type of robot you wish to build (see Exploring Robot Locomotion Systems) it’s time to turn to both the method of construction, and the materials used, for building robots. It may be a surprise to some, but building a robot is a tad more complicated than going out to the garage and cutting up a hunk of pine.

To begin, you have a choice of building the robot from scratch, using raw materials like plywood or sheet metal. Or if you prefer, you can adapt some ready-made product to serve as the base of your robot. Inexpensive house wares, hardware items, and toys can be used in various creative ways to make robot building faster and more economical.

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Locomotion involves the conversion of some source of energy — electricity, air pressure, steam, nuclear power. — into a mechanical action that moves a vehicle or other carriage. Consider the lowly car: gas you put into the tank is converted to mechanical power by means of internal combustion. The gas is compressed as a vapor and explodes against a cylinder. The explosion pushes the cylinder down; this cylinder is in turn is connected to a drive shaft, which spins the wheels. The process repeats itself thousands of times per minute.

Mobile robots use a variety of techniques to achieve motion. Most use an electric power source (usually a battery) that operates an electric motor. In the typical arrangement the direction of the motors can be changed, allowing the robot to be propelled forward or backward. There are other power train techniques used for robots, but the battery and motor pair is by far the most common.

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