# ENGRMAE 106 Lecture 2: MAE106_s2016_lab3

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MAE106 Laboratory Exercises
Lab # 3 Open-loop control of a DC motor
University of California, Irvine
Department of Mechanical and Aerospace Engineering
Goals
To understand and gain insight about how a DC motor works and how to create circuits
in order to make a DC motor spin.
Parts & equipment
Qty
Part/Equipment
1
1
Power supply
Various
Wire
1
Oscilloscope
1
Multimeter
1
Seedduino board
1
Small DC motor
1
Potentiometer
Introduction
Engineers use electric motors for a variety of applications requiring movement (robots,
automation equipment, disk drives, etc.). A motor is only useful if we can control it.
Sometimes we want to control the motor’s position (robot arms, 3d printer), sometimes
its speed (cruise control), and sometimes its torque (human-interface robots, heavy
machinery). In this lab, we will investigate controlling the voltage across a motor, which
will control the speed of the motor. The steady-state speed of the motor is proportional
to the voltage across its terminals, unless acted upon by an outside force.
In this lab we will be using simple circuits to make a DC motor spin.
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Part I: Running a DC motor with a simple circuit
To make a DC motor spin all we need to do is supply voltage across its terminals. The
amount of voltage and current needed to spin the motor will depend mainly on factors
such as the size of the motor, the speed at which we want to spin the motor, and the
load placed on the motor's shaft.
For this first portion of the experiment we will use a very simple circuit in order to make
the motor spin. We will use the power supply that is part of the equipment of the lab
(see Figure 1). This type of power supply is particularly useful for these types of
applications because we can regulate both the voltage and the current that we want to
Figure 1. Sample power supply
The two knobs - FINE and COARSE - on the right side of the power supply control the
voltage to be delivered through the power supply's connections. The two on the left
control the
maximum
current that will be delivered.
To get started, unplug any cables that may be connected to the power supply's
connections. Now turn on the power supply by pressing the 'POWER' button. On the
display on the right you will see the value at which the voltage is set. You should see a
value of 0A on the left screen since nothing is connected to the power supply and thus
no current is being drawn from it.
NOTE: Always make sure that V+ and V- are not touching. Shorting the power supply is
potentially very dangerous!
Turn the voltage knobs to set the voltage to 2.0V and turn the two current knobs to
their maximum counterclockwise (lowest/zero setting) position. Now connect the cables
to the power supply V- (black) and V+ (red) connections. Finally, connect these two
cables to the terminals of the DC motor. With these setting, your motor should not spin;
can you think about why this is?
Hopefully you realized that this was due to the setting of the maximum current which is
currently ~0A. To get your motor to spin you need to increase the setting of the
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maximum current; go ahead and turn the knobs on the left side, your motor should now
be able to spin! The motor may need a little help getting started in some cases. Give it a
nudge with your fingers if necessary.
For the next portion of the lab, turn the current control knobs all the way to their
maximum counterclockwise position (not limiting current). If you do not do this,
the power supply will limit current, and you will not get proper values!
NOTE: We will be dealing with higher currents. If the motor gets too warm, unplug it
from the power supply and wait for it to cool down before using it again.
With the motor spinning at an input voltage of 2V go ahead and stall the motor for no
more than ~2-3 seconds (i.e. hold on to the motor's shaft so that it does not spin).
What happens to the current reading on the power supply? Why does this happen?
For the final section of Part I record the stall current of the motor at 1V, 1.5V, 2V, 2.5V,
3V, 3.5V, 4V, 4.5V, and 5V. Save this data as you will need them for your lab write-up.
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find more resources at oneclass.com