AMME1705
Introduction to
Electromechanical Systems
Live Lecture/Tutorial
Week 8
The University of Sydney
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https://i.ytimg.com/vi/5nwNKPs2gco/maxresdefault.jpg
Quiz details for week 9
what is involved?
This is a quiz about sensors and signals (content before motors).
As with the week 6 quiz, high level questions about the lecture
content (as in similar style to the weekly quizzes).
More detail about lab 2 (mostly the first two weeks as there are
still people waiting to complete the 3rd week of lab 2).
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Week 8 - Admin
Group A – no lab
Group B this week is Simulation week for lab 2
in-person: please attend your timetabled lab session
Do the prework!
otherwise it will likely be a struggle to finish and demo in lab time.
Quiz Week 8 is due today!
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Week 9 - Admin
Before your marking Lab
Upload a single document of your lab book!
Your tutor will check that the file is there before marking.
After the marking session, you need to upload your shared
document.
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https://edstem.org/au/courses/20547/discussion/2579824
source
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Outline
– Review of Week 7 quiz
– Summary
– Transistors
– PWM
– Control
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Review of week 7 quiz
𝝉 ~ 0.63
𝝉 = RC
𝝉 = 1K x 100u
𝝉 = 1000 Ω x 0.0001 f
𝝉 = 0.1 seconds
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Review of week 7 quiz
𝝉 ~ 0.63
𝝉 = RC
𝝉 = 1K x 22u
𝝉 = 1000 Ω x 0.000022 f
𝝉 = 0.02 seconds
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Review of week 7 quiz
This is a high-pass filter circuit, where:
•The capacitor blocks DC and passes higher
frequencies
•The resistor completes the path to ground, allowing
voltage to be observed across it
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Review of week 7 quiz
For capacitors in parallel, the total (equivalent)
capacitance is:
Ceq=C1+C2
Ceq = 940 uF
For capacitors in series, the total (equivalent)
capacitance is given by:
1/Ceq=1/C1+1/C2.
Ceq= 235 uF
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Review of week 7 quiz
For inductors in series, the total (equivalent)
inductance is:
Leq = L1+L2
Leq = 200 mH
For inductors in parallel, the equivalent
inductance​ is given by:
1/Leq=1/L1+1/L2
Leq = 50 mH
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Where are we up to ?
Basic electronics
Sensors and signals
What is a motor, and what makes it spin
☐ open-loop vs closed-loop control (basic ideas so far)
Final lab
Provide power to, and make a closed loop motor controller
(we already have the main ideas sorted !)
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Weekly plan (remainder of the semester)
Week 7 Making things move (DC motors and interfaces)
Week 8 Delivering power (PWM and transistors)
<mid semester break>
Week 9 Tuesday 12pm - Quiz "Sensors and Signals"
Week 10 Power supplies (AC/DC, different types/options, failure modes)
Week 11 Other things that move (AC, servos , solenoids)
Week 12 Circuit analysis and review of the UoS.
Week 13 Tuesday 12pm - Quiz "Putting it all together"
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Delivering power
provide the right amount of power to a device
ideas include:
- switching power on/off
- how much power can be delivered
- what devices can control this power
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Mechanical Switches
+ Provide physical isolation of the circuit.
- Can be noisy
- takes some time to perform the action.
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Transistors
A transistor is an electronic component that can control the flow of
electricity. When used as a switch, it can turn a device (like a DC
motor or LED) on or off, just like a regular mechanical switch, but
with no moving parts.
Speed: Transistors can switch on/off very quickly, thousands of
times per second or more.
Automation: They can be controlled by tiny signals (like from a
microcontroller), so they’re perfect for automated systems.
Durability: No moving parts = less wear and tear.
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Transistors
There are many kinds, but the slide mentions two main types:
• BJT (Bipolar Junction Transistor):
• Controlled by current at the base pin.
• Good for simple, low-power switching.
• FET (Field-Effect Transistor):
• Controlled by voltage at the gate pin.
• More efficient for switching large currents, especially in power
electronics.
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Transistors BJT
BJT stands for Bipolar Junction Transistor. It’s one of the most
common types of transistors used in electronic circuits to:
• Switch things on and off (like motors, LEDs)
• Amplify signals (like audio or sensor readings)
Three terminals (NPN)
- Base (b) – Control pin
- Collector (c) – Current flows in
- Emitter (e) – Current flows out
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Transistor BJT
NPN (most common)
• Turns ON when the base is given a positive voltage (typically >0.7V).
• Current flows from collector → emitter.
PNP
• Turns ON when the base is pulled low (more negative than the
emitter).
• Current flows from emitter → collector.
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Transistor BJT
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BJT motor control
https://www.tinkercad.com/things/jxhpjUgqSgu-bjt-motorcontrol
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Transistors FET
FET stands for Field-Effect Transistor. It’s another transistor
type, but it works differently from BJTs.
While BJTs are controlled by current into the base, FETs are
controlled by the voltage applied to their gate terminal. They
don’t require much current, which makes them more efficient
for switching.
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Transistors FET
Just like BJTs, FETs have three terminals:
1. Gate (G) – the control pin
2. Drain (D) – where current enters
3. Source (S) – where current exits
You control a FET by applying voltage to the gate:
• Apply the correct voltage to the gate ➝ FET turns
ON (conducts between drain and source)
• Remove the voltage ➝ FET turns OFF
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Transistors
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FET motor control
https://www.tinkercad.com/things/6xqNCXaz83E-fet-motorcontrol
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Pulse Width Modulation (PWM)
PWM stands for Pulse-Width Modulation. It’s a technique
for controlling the average power delivered to a device,
by rapidly switching it ON and OFF.
Instead of just sending a constant voltage, PWM sends pulses.
The length of time the signal is ON vs. OFF in each cycle is called
the duty cycle.
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PWM – Parameters
Frequency: How fast the PWM is switching (e.g. 1 kHz = 1000
cycles/sec)
Duty Cycle: How much of one cycle is ON (expressed as a
percentage)
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https://exploreembedded.com/wiki/images/5/54/0_LPC1768_PWM.gif
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Pulse Width Modulation (PWM) - Frequency
Frequency in PWM is how fast the signal switches between ON
and OFF in one second. It's measured in hertz (Hz).
The frequency you choose affects how the load (motor, LED, etc.)
responds.
LED -> Visual perception
Motors -> Smooth Operation
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Pulse Width Modulation (PWM)
If you're using a 5V PWM signal:
– 50% duty cycle → average voltage is 2.5V
– 80% duty cycle → average voltage is 4V
– 10% duty cycle → average voltage is 0.5V
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Arduino ‘analog’ output
https://www.tinkercad.com/things/dQnD69zTzWg-arduinopwm-output
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Demo – LED
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Demo - Motor
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Control – Concept
Influencing how a system behaves to achieve a desired result.
You press the gas pedal in a car to speed up (you're controlling
the engine).
A thermostat controls room temperature by turning heating
on/off.
A microwave controls time and power to heat food.
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Control – Open loop
An open-loop system sends a signal to a device without
checking if it worked. It does not adjust or react to changes in
the environment or output.
Pros & Cons:
• Simple and cheap
• Not accurate under changing conditions
• Can’t respond to disturbances
https://media2.giphy.com/media/pNS3r79hWjZpH0gGTF/200w.gif?cid=6c09b952v2dwpt2ues3vu
druf1lam60ffv722hpfaqu8piat&ep=v1_gifs_search&rid=200w.gif&ct=g
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Control – Close loop
A closed-loop system uses feedback from sensors to monitor
the output and then adjusts the input to correct any errors.
Pros & Cons:
• Accurate and self-correcting
• Can adapt to disturbances or changes
• More complex and may need tuning
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Control – Components
A typical control system consists of:
1. Sensor – measures what’s happening
2. Controller – decides what to do
3. Actuator – carries out the decision
4. Setpoint – the desired goal
5. Feedback – compares actual output to desired output
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Temperature Control
Let’s say your cat, Walnut, loves to nap when the room is
exactly 25°C.
This is your goal — the setpoint.
25°C
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Temperature control
You use a temperature sensor (like a thermometer or thermostat) to
measure the room’s current temperature.
You check the sensor. If it’s too hot or cold, you decide what to do.
You use an actuator to actually change the environment:
- Turn on the heater if it’s cold
- Turn on the fan or A/C if it’s hot
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Temperature control
After adjusting the temperature, check again.
This feedback loop continues until Walnut’s content.
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Bang Bang controller
A Bang-Bang controller (also called on-off control) is the simplest
type of control system. It has only two states:
ON (full power) or OFF (no power) — like a light switch.
There’s no in-between, no gradual adjustments. It's like saying:
– “If it’s too cold, turn the heater ON. If it’s warm enough, turn it
OFF.”
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Bang Bang controller
Pros of Bang-Bang Control
• Super simple to implement
• No need for complex math or tuning
• Good enough for basic control systems
Cons of Bang-Bang Control
• Causes oscillation (system keeps bouncing back and forth)
• Not energy-efficient (always full power)
• Can wear out components with rapid ON/OFF switching
• Not good for precision control
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Control systems
A bang-bang controller would be unstable and uncomfortable
– A servo would oscillate between full speed forward and full speed
reverse
– Cruise control would be jerky
Ideally, would like to have a control action that depends on how close to
the set point you are
– Large acceleration when far from the desired set point
– Small acceleration when almost at the desired set point
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P = Proportional Control
This part responds based on the size of the error:
Error=Setpoint−Actual Temperature
Bigger error = bigger correction.
PRO: Simple and fast
CON: Might overshoot
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P = Proportional control
i.e.
speed sensor reads 0.5V, desired is 2.5V
control voltage = Kp * (2.5 - 0.5)
Note: A large value of Kp is a bang-bang controller
A large gain is similar to why the open loop op-amp acts
as a comparator
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P = Proportional control
The idea is pretty simple - you have a system such as a motor
that you want to make go a particular speed (that you can
measure)
- If the motor is not going fast enough, you want the voltage
to be higher
- If the motor is going too fast, you want the voltage to be
lower
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P = Proportional control
The idea is pretty simple - you have a system such as a motor
that you want to make go a particular speed (that you can
measure)
- You need to measure the difference between how fast you
want to go, and how fast you are currently going, and
multiply this value by how forceful you want the controller
to be.
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P = Proportional control
A range of Kp values
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Integral control
Proportional control cannot reach the actual set point
– Approach the set point, the error gets smaller and smaller
– The control action approaches zero
– Not enough to force the system the last bit of the way
– Friction, inertia, noise, etc
This generally leads to a steady state error
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I = Integral control
Take the error and add it up over time, it gets bigger the longer
the error exists
– Use this summed error as an additional control action
– The longer the error exists, the more the controller will push
toward the set point
– The sum is generated by integrating the error
Control action += Ki * integration of error
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https://controlguru.com/wp-content/uploads/2015/08/piintbig.jpg
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I = Integral control
There are some challenges:
– Choosing the best value is not easy
– The integral term can lead to overshooting and oscillation
If only there was a way we could limit the rate of change of the
signal ?
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D = Differential control
Differential control is a control action that punishes fast changes
in the measured error
– The control action is proportional to the change in error
– A positive change in error leads to a negative control action
which dampens the system
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PID control
PID = Proportional Integral Differential
Put this together and you have probably the most common control strategy
using in many, many devices
- Good because it is simple, very fast to compute
- Can do this using only op amps (no microcontroller)!
Control action = Kp * error
+ Ki * accumulated error
+ Kd * change in error
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Demo
https://www.luisllamas.es/en/pid-controller-simulator/
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https://content.spiraxsarco.com/-/media/spiraxsarco/global/learn-about-steam/8---control-applications/fig-8-35.ashx?h=455&w=900&rev=dc1be3fa69074e758c0117f8bdd54e05&hash=2E415A6A4681B493A4BEDABDF0CC3F82
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Lab 3 - Driving a motor
In the next lab, we will be doing this using the arduino as the
controller.
We will drive the motor using PWM from the analog output of
the arduino, and make an encoder to measure the speed from
which we can determine the control action.
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Analog output only with ~
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