The period of the pulse that is sent determines where (0' to 180') to place the head. Different servo manufacturers require different pulse-widths, so you have to experiment a little to find the pulse-widths that correspond to each position. For example, the Futaba servo has a 900 position (middle) pulse-width of about 1.5 Ms. This means that if you send a 1.5 Ms pulse to the servo at least once every 20 Ms, the servo will move to, and hold at, it's 90' position. If you try to turn the head with your hand you will feel the servo forcing against you, trying to keep the 900 positions.

             In practice, you can send pulses more often that once every 20 ms; you can send them less often as well, but if you don't send any pulses for about 50 ms or so, the control electronics in the servo "go to sleep" (enter a power-saving mode). Don't forget, servos were designed for R/C airplanes and cars, where battery life is important. When a servo powers-down, it no longer works against an applied force to maintain its position. You will find that even then the head is fairly difficult to turn.

 

DC Motors

            DC motors are widely used in robotics for their small size and high energy output. They are small and powerful. Typical DC motors operate on as few as 1.5 volts on up to 100 volts. Robotics often use motors that operate on 6, 12, or 24 volts. DC motors run at speeds from several thousand to ten thousand RPM. A low voltage (e.g., 12 volt or less) DC motor may draw from 100 milliamps to several amps at stall, depending on its design.

Main Characteristics of DC Motors: High Speed, Low Torque, Reversibility Motion.

          The power of a motor is the product of its speed and torque. This means maximum speed no torque, maximum torque minimum speed. Motors that draw more current will deliver more power. Also, a given motor that draws more current delivers more output torque. Current ratings are often given when the motor is stalled by producers of motors.

           Application of voltage difference on the two poles of a motor creates the rotation of the output shaft. Direction of rotation depends on the polarity of the potential applied to change the polarity in order to reverse direction. In order the quick stop, connect the poles (create a shortcut between poles) of the motor. Note that if you preserve this state you will harm the motor. So, use this method for instantaneous applications.

Light Sensors

The infrared spectrum, IR, falls between the visible light and microwave spectrums. This wavelength range between 750 nm to 1,000,000 nm is called the infrared region. Infrared waves are electromagnetic waves with wavelengths longer than visible light. The heat you feel from a fireplace, campfire or sunlight is source of infrared radiation.

IR light is used in a variety applications such as TV remote controls, heating and drying, night vision equipment, and of course sensors.

--IR Sensor Types

Optical IR sensors typically are classified as reflective and transmissive. Both types contain an IR photo diode to emit the light and an IR photo detector to sense the emitted light. The difference lies in light's path. With a reflective sensor, the light strikes the target and is reflected back to the detector. With a Transmissive detector, the photo diode and detector are pointed at one another, and the target interrupts the beam path.

Ranging sensors measures the distance of the target from the sensor.  These sensors are limited to reflective sensors because of the required emitter/detector topology.

IR ranging sensors are particularly useful for solving robotics and navigation problems. The presence sensors are more useful as mechanical position sensors, such as in a limit switch application.

Types of IR sensors,, data sheets of  IR sensors, web pages of poducer companies, and possible usage circuits will be here!