Actuators: Where the REAL
Action Takes Place!
Fred Donelson
Kevin McKone
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
Most Common ROV Actuators:
• Motors
• Solenoids
• Pneumatics and/or hydraulics
Let’s start with motors:
A motor might turn some gears:
Or a propeller
Two important factors/variables to
control with motors
• Direction that the motor axle turns
• Speed at which the motor axle rotates
Here is a simple circuit with a power
source and the motor as a load:
The red arrows show the direction of
the current flow
Spin Direction
of Axle
By flipping the battery terminals, the
direction of the motor rotation can be
changed
Motor
Spin Direction
of Axle
Of course, continually
flipping the terminal
connections would get old
very fast!
Another way to change
directions is to use a
double pole/double throw
switch
First, we make
these connections
When the switch
is in the center
position (B & E),
no current flows
(off)
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.
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
Many ROVs
use three of
these DPDT
switches to
easily control
the direction
of three
motors
However, there is one drawback:
The DPDT switch only has ONE SPEED!
It is either all the way on, or all the way
off!
And after a while, your fingers get
tired of pushing those switches too!
And even if we didn’t get tired,
there’s a limit as to how fast we
can mechanically flip the switch
each second.
Fortunately, there are
ELECTRONIC DEVICES
called transistors that can
act as switches for us!
One type is known as a
Metal Oxide Semiconductor Field
Effect Transistor:
MOSFET
These electronic switches can turn
on and off several thousand times
a second
When connected to a
controller/computer, one can vary
the speed as well as the direction
of a motor!
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
This is known as Pulse Width
Modulation (PWM)
Each MOSFET and controller can
control how long the motor is on
(which is called it’s duty cycle)
But it takes 4 MOSFETS arranged in
a special arrangement called an
H – Bridge to actually change the
direction of a motor
It works similar to a DPDT switch
Basically two
MOSFETs lead
from the
positive
terminal and
two from the
negative
If P1 and N2 are
turned on, the
current travels
from left to
right through
the motor
(black arrows)
If P2 and N1 are
turned on, the
current travels
from right to
left through the
motor (red
arrows)
You can learn more about how the
H-Bridge works by checking out
page 519 in your textbook!