Actuators: Where the REAL Action Takes Place!

1. Actuators: Where the REAL Action Takes Place! Fred Donelson Kevin McKone

2. What is an Actuator? • It is a mechanism that converts some type of energy into motion in order to do work (move a force over a distance) • The three common types of energy used in ROV work are electrical current, hydraulic pressure, or pneumatic pressure

3. Most Common ROV Actuators: • Motors • Solenoids • Pneumatics and/or hydraulics

4. Let’s start with motors:

5. A motor might turn some gears:

6. Or a propeller

7. Two important factors/variables to control with motors • Direction that the motor axle turns • Speed at which the motor axle rotates

8. Here is a simple circuit with a power source and the motor as a load:

9. The red arrows show the direction of the current flow Spin Direction of Axle

10. By flipping the battery terminals, the direction of the motor rotation can be changed Motor Spin Direction of Axle

11. Of course, continually flipping the terminal connections would get old very fast!

12. Another way to change directions is to use a double pole/double throw switch

13. First, we make these connections

14. When the switch is in the center position (B & E), no current flows (off)

15. When the switch is in the up position (connecting B to A & E to D), notice the current (red arrows) flows through motor from left to right.

16. When the switch is in the lower position (B to C & E to F), current flows from right to left through the motor, thus changing the direction of spin

17. Many ROVs use three of these DPDT switches to easily control the direction of three motors

18. However, there is one drawback:The DPDT switch only has ONE SPEED!It is either all the way on, or all the way off!

19. And after a while, your fingers get tired of pushing those switches too!

20. And even if we didn’t get tired, there’s a limit as to how fast we can mechanically flip the switch each second.

21. Fortunately, there are ELECTRONIC DEVICES called transistors that can act as switches for us!

22. One type is known as aMetal Oxide Semiconductor Field Effect Transistor:MOSFET

23. These electronic switches can turn on and off several thousand times a secondWhen connected to a controller/computer, one can vary the speed as well as the direction of a motor!

24. A very fast switch can turn the motor on (12V) or off (0V), and the controller can control the average time the motor is on each second, affecting its speed

25. This is known as Pulse Width Modulation (PWM)

26. Each MOSFET and controller can control how long the motor is on (which is called it’s duty cycle)

27. But it takes 4 MOSFETS arranged in a special arrangement called anH – Bridge to actually change the direction of a motorIt works similar to a DPDT switch

28. Basically two MOSFETs lead from the positive terminal and two from the negative

29. If P1 and N2 are turned on, the current travels from left to right through the motor (black arrows)

30. If P2 and N1 are turned on, the current travels from right to left through the motor (red arrows)

31. You can learn more about how the H-Bridge works by checking out page 519 in your textbook!