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Last updated on Wed Dec 22 10:24:57 IST 2010.

Actuators

Actuators are the working limbs and hence the most conspicuous parts in a robot. Actuators take different forms depending on the need. Most actuators produce motion and use some kind of a motor. Another useful kind works with light, and are used a displays. The simplest example is a light emitting diode (LED). A liquid crystal display (LCD) is a more sophisticated example. Other forms of actuators include sound producing devices (buzzers, speakers etc), heating elements.

From the view point of the user the different actuators are quite different. But from the view point of the builder of the robot, the actuators are basically of three types:
  1. Weak, stupid devices: These are weak devices in the sense that they can be driven with low voltage (e.g. 5 V) and feeble current (a few milli amp). These are stupid in the sense that they are binary devices that produce output the momen they are given power. Not many useful devices belong to this category. However, these are the simplest devices to work with, and hence are useful for debugging a robot. LEDs abd buzzers are the most promiment members of this genre.
  2. Strong, stupid devices: These are stupid, but need either high voltage or high current. These include all power tools like motir, heating elements. Even a toy motor requires pretty high current.
  3. Weak, clever devices: These include devices like LCD s that is capable of producing complex output. Often these devices are themselves have tiny computers embedded in them, or are small robots themselves.
Each of the three categories is interesting in its own right. The first category is ueful because of its absolute simplicity. The second category is needed for most useful jobs requiring motion. The third category is mostly used by a robot to communicate with human users.

Weak, stupid devices

The most important of this category is a LED. A few points are in order here:
  1. LEDs when on have only about 1.5 V across them. So when using a power supply with higher voltage you must connect the LED in series with a resitor (1K being a typical value).
  2. A LED has polarity. You must connect them in the right orientation. If connected in the reverse direction it will not light up (but not burn out).
  3. It is perfectly OK to connect a LED to a higher power supply (up to something like 36V) provided you connect a high enough resistor in series. This won't harm the LED.
An array of 8 LEDs is a very useful thing to have handy. So if you want some practice with soldering then implement the following circuit.

A typical implementation may be like this.

A buzzer is much like a LED, except that it has no polarity.

Strong, stupid devices

These are definitely the most exciting actuators because they do the actual work (moving the robot, gripping a tool, heating something). If you want your robot to operate a vacuum cleaner, for example, then you are in this category. The way robots deal with strong, stupid devices is much like the way we hiuman beings do: using a switch. The only difference is that these switches are electrically operated. There are different types of such switches possible. But the most basic type is a buffer. Another form is a relay. Often one has to cascade multiple switches to turn on stronger devices.

There are different types of motors: DC with brushes, DC without brushes, stepper, servo.

Weak, clever devices

We cannot discuss these devices until we learn about microcontrollers.
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© Arnab Chakraborty (2010)

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