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STIP - RActuators:

DC Motor:

The most commonly and widely used actuator is a simple DC motor. Apply a voltage

to both terminals, and weeeeeeee it spins. But what if you want to control which

direction the motor spins? Correct, you reverse the wires. But you cant directly

connect a wheel to the motor unless the robot is small and light weight. This is

because a DC motor spins at a very high speed while delivering a very low torque.

So to reverse this effect we need something in-between; like a transmission gear

box in car. But over here we call it a gear-box. And the resultant arrangement is

know as the geared motor.

Important Geared Motor Parameters:

Coil ResistanceThe resistance between the motor terminals.

VoltageThe rated operating voltage of the motor.

No load CurrentCurrent measured flowing through the motor in the free running (no load) condition.

Stall currentCurrent measured flowing through the motor in the stall (full load) condition.

TorqueThe output force of the motor, measured in Kgcm

Gear RatioIts the ratio of the number of teeth on the input gear to the number of teeth on the

second gear (one stage reduction)

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Actuators

Rotational Linear

PneumaticsDC Motors Stepper Motors

Geared RC Servo BipolarUnipolar

Artificia

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Muscle

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STIP - RRC Servo Motor: The term servo is an automatic device that uses error-sensing

feedback to correct the performance of a mechanism. RC servo motors are

composed of a DC motor mechanically linked to a potentiometer. Pulse-width

modulation (PWM) signals sent to the servo are translated into position commands

by electronics inside the servo. When the servo is commanded to rotate, the DC

motor is powered until the potentiometer reaches the value corresponding to thecommanded position. The servo is controlled by three wires: ground (usually

black/orange), power (red) and control (brown/other colour). The servo expects a

pulse every 20 ms in order to gain correct information about the angle. The width of

the servo pulse dictates the range of the servo's angular motion.

Running Servo Motors: To run a servo motor you have to generate PWM signals

at fixed time period(20ms). The on period ranges from 1ms to 2ms corresponding to

0 degree to 180 degree. A servo pulse of 1.5 ms width will set the servo to its

"neutral" position, or 90 or servo pulse of 1.25 ms could set the servo to 45.

Stepper Motor:

Stepper Motors work under a very similar principle to DC motors, except theyhave many coils instead of just one. So to operate a stepper motor, one must

activate these different coils in particular patterns to generate motor rotation. So

stepper motors need to be sent patterned commands to rotate. These commands

are sent as high and low logic over several lines, and must be pulsed in a

particular order and combination. Steppers are often used because each 'step,'

separated by a set step angle, can be counted and used for feedback control. For

example, a 10 degree step angle stepper motor would require 36 commands to

rotate 360 degrees.

Drivers:

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http://en.wikipedia.org/wiki/Feedbackhttp://en.wikipedia.org/wiki/Pulse-width_modulationhttp://en.wikipedia.org/wiki/Pulse-width_modulationhttp://en.wikipedia.org/wiki/Feedbackhttp://en.wikipedia.org/wiki/Pulse-width_modulationhttp://en.wikipedia.org/wiki/Pulse-width_modulation

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Since current and voltage requirements of a motor are higher than what a logic

block can provide, we need an amplifying or a driving device in-between them.

The driver could be an electromechanical or a solid state device.

H Bridge Designs:

How to run a DC motor in both directions?? A H-bridge is an electronic circuit whichenables a voltage to be applied across a load in either direction. A "double pole

double throw" relay can generally achieve the same electrical functionality as an H-

bridge. This is how the H-bridge configuration looks:

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Drivers

Electromechanical Solid-State

Relays

(SPST,SPDT,DPST,DPDT)

BJTs &

MOSFETs

http://en.wikipedia.org/wiki/Electronic_circuithttp://en.wikipedia.org/wiki/Relayhttp://en.wikipedia.org/wiki/Electronic_circuithttp://en.wikipedia.org/wiki/Relay

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S2 and S3 Closed S1 and S4 Closed

The first diagram above is a H-Bridge configuration. Let us now see the working inthe next figure. When we close the switch S2 and S3 the current flows in thedirection as shown in the figure. When we close the switch S1 and S4 the currentflows in the opposite direction as shown in the figure. Now if we close the S1 and

S3, the Vcc and GND are directly shorted which will burn the circuit. If we close theswitch S1 and S2 the motor will stop working.

Now how do we implement this logic in a circuit? The switches inelectronics are transistors. Now as we must not close switches S1,S3 or S2,S4together we use complementary pair of transistors so that S1,S3 or S2,S4 doesntget shorted. The complementary pair of transistors are PNP and NPN transistors. Sowe will now replace these switches by PNP and NPN transistors.

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Now let us look at the above circuit keeping in mind the working of H-Bridge. Let usstart giving different inputs to A and B and see how circuit reacts to these inputs.

Case 1:

A B T1 T2 T3 T4

0 1 ON OFF OFF ON

In this casewhen T1and T4

areON themotor

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STIP - Rmoves in the clockwise direction. When A is 0 T3 doesnt get ON since NPNtransistor gets ON when input is given as 1.Similarily when B is 1 T2 doesnt get ONsince PNP transistor gets ON when input is given as 0.

Case 2:

A B T1 T2 T3 T4

1 0 OFF ON ON OFF

In this case when T2 and T3 is ON the motor moves in the anti-clockwise direction.When B is 0 T3 doesnt get ON since PNP transistor gets ON when input is given as0.Similarily when A is 1 T1 doesnt get ON since NPN transistor gets ON when inputis given as 1.

To protect the transistors we add four Fly back diodes in parallel as shown in figurebelow.

The same design is implemented in the motor driver board given to you.

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STIP - RL293D motor driver board: H-bridge Configured motor driver

The motor driver board is built around the popular L293D H-bridge IC. It is used for

driving two DC motors bidirectional or to drive one stepper motor. It is widely used

to drive medium voltage & current rated motors. It can source as well as sink

current of 600mA. The supply voltage rating is up to 36V. It has a feature of inbuilt

flyback diodes.

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