ECE5320 Mechatronics Assignment #1: Literature Survey on Actuators DC Motor Servos

1. ECE5320 MechatronicsAssignment #1: Literature Survey on Actuators DC Motor Servos Prepared by: Robert Silver Dept. of Electrical and Computer Engineering Utah State University 3/10/2006

2. Outline • Reference list • To probe further • RC Car Servo • Basic working principle illustrated • A typical sample configuration in application (application notes) • Major specifications • Limitations • Commercial servo motors and examples ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

3. Reference list • http://zone.ni.com/devzone/conceptd.nsf/webmain • http://www.allegromicro.com/techpub2/compumot/a03.pdf • G:\mechatronics\Intro to RC Servos.htm ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

4. To explore further (survival pointers of web references etc) • http://zone.ni.com/devzone/conceptd.nsf/webmain • www.globalspec.com • http://www.allegromicro.com/techpub2/compumot/a03.pdf • http://www.electricmotors.machinedesign.com/ • http://www.aerotech.com/products/amps/amplifiers.html • http://www.netmotion.com/htm_files/mc_servo_driver.htm ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

5. RC Car Servo Major applications • Steering motor for rc cars • Positioning of a shaft • Reversible positioning • Motion control ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

6. RC Car SERVO Example • Controlling of the servo motors is used using pulse controlling. • The control pulse is positive going pulse with length of 1 to 2 ms which is repeated about 50-60 times a second. Details in the figure below: • Sending 1 ms pulses sets the servo to one end position and sending 2 ms pulses sets it to the other end position. Sending 1.5 ms pulse sets the servo motor to the center position. 5vdc 1-2 ms 18-25 ms ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

7. Theory of Driving RC servos • The pulse width to the servo is the most important deciding factor of its desired position • Frequency of the pulses must be within a certain range for servo operation • A 10 µSec pulse width increase results in about a degree of movement on the output shaft, however this varies some from manufactures to manufactures • The Servo has built into it position feedback sensor • The Servo has built into it a closed loop position control system • Thus the position of the servo motor is dependant on the pulse width and frequency it receives. ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

8. Controlling an RC Car Servo Here a 555 timer circuit is used to drive the servo motor with a pulse. This pulse is adjustable from the 100k pot which will adjust the pulse width and hence the position of the servo. ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

9. Typical Movement Limits of RC Car Servos Most vary from approximately -45° to +45 ° Some only have a 45 ° range of motion ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

10. More RC Technical Data • The motors inside a RC car servo are not like a stepper motor. They rotate many times before the output shaft of the servo has moved 180 °. This is due to set of gear reducers. • The output shaft gear is connected to a arm that is sensed by a simple position sensor. The RC servo has a simple built in controller that determines the appropriate position of the output shaft according to the pulses given it from the timer control input. ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

11. Approximate Size of Small RC Servo G:\mechatronics\Intro to RC Servos.htm ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

12. Applications of Small RC Servo • For the steering motor in an RC car • For the rudder in a RC airplane • The aileron in an RC airplane • For control animation purposes • Small robot applications ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

13. Multiple Servo Applications and Wiring http://gbaxport.sourceforge.net/rcservo.pdf ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

14. Pros of RC type servos • Small and compact • Lightweight • Very inexpensive for pwm control movement • The web has lots of information on how to build a simple pwm controller for these small servos ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

15. Cons of RC type servos • Movement is restricted to 200 ° maximum, some to only 45 ° • Torque output is small, so can’t turn heavy devices • Very precise angular movement not feasible ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

16. Commercial DC Servo Motors • High torque and load applications • High speed positioning • High resolution • Very rugged design ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

17. Commercial Servo Motor http://zone.ni.com/devzone/conceptd.nsf/webmain/0B12F0C5C73B63008625680A004951CD ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

18. DC Servo Motors Fundamentals` • Ability to operate at many different speeds • Ability to operate at zero speed or low speeds for a sustained period. • Retains sufficient torque to hold a position under a load • Some have encoders built into them • Others that are driven by a variable frequency drives don’t need encoders for speed, but for position they do ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

19. Commercial Application http://zone.ni.com/devzone/conceptd.nsf/webmain Motor turning worm drive to position conveyer belt full of bottles into the right place ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

20. Another Example http://www.allegromicro.com/techpub2/compumot/a72a96.pdf DC or ac servo motor being used to position steel plate into the correct location for cutting, note the servo controlled by a pulse drive ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators