example of different dc motors

8/11/2019 Example of Different Dc Motors

1/22

D Motor

Presented by

SRIKANT PATI

CENTRAL TOOL ROOM AND TRAININGCENTER


2/22

Example of Different Motors

DC (brushed)

Stepper

RC Servo

Solenoid


3/22

DC (brushed) Moto r

DC (brushed)

Stepper

RC Servo

Solenoid

Workhorse, high powerSimple to use, two wires

Torque proportional tocurrent, steady stateconstant-load speedproportional to voltage

Requires gearing

Requires feedback


4/22

Stepper Mo tors

DC (brushed)

Stepper

RC Servo

Solenoid

Useful for low-torqueapplications with nosurprises

No feedback required

One step per pulse

More involved driving circuit


5/22

RC Servo Motors

DC (brushed)

Stepper

RC Servo

Solenoid

High torque, useful forpositioning applications

Feedback and gearing built in

Position commanded bypersistent pulse train

Limited motion (less than 1revolution)


6/22

Solenoid

DC (brushed)

Stepper

RC Servo

Solenoid

For on-off applications

Simple to useShort stroke

Powered in only onedirection; requires external

spring for return


7/22

DC Motors

Lorentz Force Law:F = I x B

F = force on wire

I = current

B = magnetic field

Right hand rule:

index finger along I,

middle finger along B,thumb along F

N S


8/22

Inside a DC Motor


9/22

DC Motors

V = IR + L (dI/dt) + kewt= kt I

V voltage

I currentR resistance

L inductance

w speed

t torque

ke electrical constant

kt torque constant

2 - permanent magnet3 - housing (magnetic return)4 - shaft5 - winding

w

t

speed-torque curvesfor two voltages


10/22

DC Motor Specs


11/22

Driving a DC Motor

Switches and relays Transistors

Linear push-pull stage with op amp

Ideally: H-bridge and PWM


12/22

H-bridge and PWM

PWM: Rapidly switch betweenS1-S4 closed and S2-S3 closed

Averages to effective voltageacross motor between -V and+V depending on time spent inS1-S4 and S2-S3 states

Switch control signals are simply

digital signals

Use an H-bridge chip or build outof transistors


13/22

L293 H-bridge chip


14/22

Practical Issues

flyback diodes for inductive kick heat sinks for transistors

capacitors to smooth voltage spikes

other noise issues, isolation


15/22

Gears

Gear ratio Gwout = win/ G

tout = hG tin (h= efficiency)

Many typesspur, planetary, worm, lead/ball screw, bevel,harmonic...


16/22

Encoder Feedback

Another option:potentiometer

US Digital


17/22

Feedback Control

Proportional (Integral-Derivative) ControlMultiply position/velocity error by a gain to get controlsignal (and perhaps add integral and derivative ofthat error multiplied by other gains)

Usually implemented on computer

Can be implemented with op amps


18/22

Stepper Motor

Bipolar: 4 wires

Unipolar: 5 or 6 wires

+V alternately ground one

end of coil or other

1 42 3A B

A B

R RRR L

LL LLL R

RRL


19/22

Animation of Unipolar

Taken from http://www.cs.uiowa.edu/~jones/step/


20/22

Driving a Stepper

Use logic on/off signals at 2, 7, 10, 15.


21/22

RC Servo Motor

3 wires: power, ground, control

Control signal sets the position.

High pulse every ~20 ms determinesset angle; pulse width between~0.5 ms and ~2 ms, indicating thetwo ends of angle range

Internal gearing, potentiometer, andfeedback control.


22/22

Solenoid

Plunger attracted or repelled by currentthrough a coil.

May be driven by a relay or transistor.

example of different dc motors

Documents