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Remotely Controlled Vehicles Introduction: A remote controlled vehicle contains several parts which work together and can be directed through an array of commands sent through the air via radio frequencies. A typical vehicle is comprised of a servo, used for steering, a drive motor, used for speed control, a transmitter, and a signal receiver. Each component will be described below to outline how the vehicle is controlled. Servo: A servo is a motor that is used to turn the steering wheels of the vehicle or possibly the rudder on a boat. Every servo contains three wires; a power wire which needs a constant 3-7 volts, a ground wire which has 0 voltage, and a control wire that contains a varying voltage or alternating signal. The control wire is what enables the servo to turn the vehicle. An alternating signal has a specified period, voltage magnitude, and duty cycle. The period is the time it takes for a signal to go from one rising edge to the next as indicated in the figure. The voltage magnitude is the voltage reached at the highest point in the signal. The duty cycle is a percentage of a signal period that the voltage is high as indicated in the chart. For a typical servo the period is in the range of 20-30 milliseconds. A leftward turn is performed when the control wire is given a wave with a 0 – 6% Duty Cycle whereas a rightward turn is done with a 7 – 15% Duty Cycle. This is a critical part of the system but is not effective in a stationary vehicle which is where the Drive Motor comes into play. Rising Rising Edge 1 Edge 2 Period Drive Motor: The Drive Motor is what controls the speed of the vehicle. Unlike the servo this motor contains only two wires, the ground wire and the power wire. The ground wire will always be black and should have zero voltage. On the other hand, the power wire is typically red and has a voltage that varies between zero and 5 volts. The Drive Motor is usually given a duty cycle to change the speed. However, in this case the period of the signal will likely be less than 5 milliseconds and the Duty Cycle will vary from 0, no motion, to 100%, full speed. Transmitter: The transmitter is the remote used to control the vehicle and varies in appearance from vehicle to vehicle. Some examples of what this might look like are displayed below. Regardless of the transmitter the same functions typically exist and include the following: Forward Forward and Right Forward and Left Reverse Reverse and Right Reverse and Left A radio transmitter has a designated frequency or times per second that it has a rising edge. Each of the actions above has a certain amount of pulses that are sent when requested. The pulses vary between 2.1 milliseconds and .7 milliseconds. The pulses repeat for as long as the action is requested and then stop. As seen in the figure below the four 2.1 millisecond pulses at the start of the transmission warn the receiver that an action is being requested. Then, the numbers of short pulses, ranging from 0 – 60, are counted by the receiver to determine the action. So, for example, forward may be designated by 16 pulses and reverse by 52 pulses. Receiver: The signal sent by the transmitter is interpreted and decoded by the receiver to perform the action. The logic or information embedded within the circuit board will contain instructions for the different number of pulses. If the antenna receives 16 short pulses, a request to go Forward, the circuit will turn on the drive motor with a 100% duty cycle and set the steering to a duty cycle which sets the wheel to go straight(~6.5% duty cycle). The same process is done for all other actions to control the vehicle. Total Operation: Remotely controlled vehicles are used primarily for toys but are becoming more and more prevalent in automated actions and in the war on terror. Planes are now performing actions overseas while being operated by pilots on the ground in the United States. Vehicles are also becoming much more intricate with lights, cameras, and in some cases even weapons. They are progressing towards operation at higher frequencies for faster response times and greater range. As technology progresses the possibilities of the Remotely Controlled Vehicle is sure to do the same.
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