Seminar 7 - Ethical Conduct and Integrity
Notes
CRICOS code 00025B
How do I know if EMI is a problem in
my robot?
Potential symptoms include:
• Servo jitter
• Arduino power cycles or even dies
• Sensor read-outs are inconsistent
• Power supplies are noisy
• Controllers relying on reference signals
that stop working as expected
EMI – Electromagnetic interference
35
CRICOS code 00025B
Motors are inductive loads
What does that mean?
In a nutshell:
On start-up, motors can have a
large IN-RUSH CURRENT
• Mitigate by decoupling power rails
with capacitors
On slowing down, motors
discharge their BACK EMF
• Mitigate with flyback diodes
36
CRICOS code 00025B
What can EMI look like in the real world?
Example project:
• Design and build of electronic-load to calculate power generation of wind-turbine
37
CRICOS code 00025B
EMI example - The Problem
Inconsistent readings between setpoint
and feedback
Measured large back-EMF that was
outside sampling frequency
38
CRICOS code 00025B
EMI Example - Solution
Where:
𝑎𝑎𝑐𝑐 =inrush current (A)
𝐶𝐶 = capacitance F
𝑑𝑑𝑉𝑉 = change in voltage (V)
dt = change in time (s)
Add filtering capacitor:
“Ohm’s Law” for capacitance:
𝑎𝑎𝑐𝑐 = 𝐶𝐶 𝑑𝑑𝑉𝑉
𝑑𝑑𝑐𝑐
80 = 𝐶𝐶 × 132
1/3000
𝐶𝐶 = 80 × 1/3000
132
𝐶𝐶 ≈ 200 𝜇𝜇𝐹𝐹
39
CRICOS code 00025B 40
EMI Example - Solution
CRICOS code 00025B
Transmission Systems
We need more torque!
41
CRICOS code 00025B
Transmission Systems
Why use a transmission?
• Need to match the torque from the
actuator to the load requirement.
• Rotational to rotational motion
- Reduce speed and increase
torque - Change direction of rotation
Input: Faster,
lower torque
Output: Slower,
higher torque
42
CRICOS code 00025B
Transmission Equations
Speed (no losses)
Relationship between number of teeth (𝑁𝑁) and
speed (𝜔𝜔): 𝑁𝑁1 𝜔𝜔1 = 𝑁𝑁2 𝜔𝜔2
Speed reduction ratio:
𝜔𝜔2 = 𝑁𝑁1
𝑁𝑁2
𝜔𝜔1
Torque (no losses)
Relationship between number of teeth (𝑁𝑁)
and torque (𝜏𝜏): 𝜏𝜏1
𝑁𝑁1
= 𝜏𝜏2
𝑁𝑁2
Torque conversion becomes:
𝜏𝜏2 = 𝑁𝑁2
𝑁𝑁1
𝜏𝜏1
𝑁𝑁1
𝑁𝑁2
𝜔𝜔1 𝜔𝜔 2
𝑁𝑁1 𝑁𝑁2
𝜏𝜏1
𝜏𝜏 2
43
CRICOS code 00025B
Image References
Fallen Crane
https://www.brisbanetimes.com.au/national/queensland/crane-crashes-
down-outside-brisbane-shopping-centre-20180123-p4yyr3.html
Stress-strain curve
https://upload.wikimedia.org/wikipedia/commons/thumb/c/c1/Stress_str
ain_ductile.svg/710px-Stress_strain_ductile.svg.png
Yellow DC Motor
https://images-na.ssl-images-
amazon.com/images/I/611DaaG9WbL.AC_SY355.jpg
Garage
https://brisbanerollerdoors.com.au/wp-
content/uploads/2019/02/IMG_3578-4032x2016.jpeg
Phone Vibration Motor
https://www.ifixit.com/Guide/Nexus+6P+Vibration+Motor+Replacement
/104467
Misaligned Bridge
https://www.snopes.com/fact-check/misaligned-bridge-photo/
Car Electric Motor
https://i.pinimg.com/474x/c0/ee/4c/c0ee4cd52228ff61520a22e014e1a8ce—
electric-motor-electric-vehicle.jpg
Truck
https://www.theverge.com/2019/8/15/20805994/ups-self-driving-trucks-
autonomous-delivery-tusimple
F1 race car
https://www.formula1.com/en/latest/article.ferrari-boss-binotto-rates-mick-
schumachers-progress-in-first-year-of-f1.19YvFMVUT4wPd0TOOUxxr2.html
DC Motor
https://i2.wp.com/sciencestore.pk/wp-content/uploads/2020/03/dc-motor-
6V.jpg?fit=600%2C600&ssl=1
Wheel
https://www.stanleyproducts.com.au/static/uploads/images/97-stwbp100-
1181x1181-1-wfrltzkhowrs.jpg?mode=max&upscale=true&width=768
Gear GIF
https://upload.wikimedia.org/wikipedia/commons/thumb/b/bd/Animated_3_Gea
r_Row.gif/1200px-Animated_3_Gear_Row.gif
44