Introduction to Robot Subsystems
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Transcript Introduction to Robot Subsystems
Presented By:
Lynbrook Robotics, Team 846
John Chai, David Liu, Aashish Sreenharan,
Michael Wachenschwanz, and Toshi Tochibana
Available online at lynbrookrobotics.com
Tech > Resources > “WRRF Presentations”
Talk Outline
Pneumatics
Sensors and Electronics
Electrical Components
Robot Drive Train Design
Michael Wachenschwanz and Toshi Tachibana present…
Pneumatics
Can you feel the pressure
Pneumatics is the use of pressurized air to
achieve mechanical movement.
Air tends to move from high pressure to low
pressure
Important note: There is no such thing as a
negative pressure
Compressor
Where it all starts
The compressor takes air
from the surrounding
atmosphere and compacts
it via pistons.
Comes with a release
valve attached to it
Pressure Switch
Better safe than sorry
Safety Mechanism
Turns the compressor off
at 120 psi and turn it
back on at 115 psi
Tubing and Fittings
Keeping connected
Tank
The more the merrier
Tanks allows more air
in the system.
When air is lost, psi
drop is mitigated by
larger tanks
Plug Valves
Done for the day
Releases all the
compressed air in the
system.
Must be release
manually
Be sure to release the
stored air when done
with the system
Regulator
Stay in control
Regulators regulate the
pressure.
Uses air from input to
maintain the pressure of
the output
Usually kept at 60 psi
for FIRST competitions
Electric Valves
Handling the pressure
Single and double
solenoid valves are used
Controlled by the control
board via electricity
Double solenoids
exposes one port to
pressure and the other
to the surrounding
atmosphere
Actuators
Use the force
Actuators convert the difference in air
pressure to mechanical motion
Linear actuators, or cylinders, are the more
common actuators. For the competition, they
come in 3 bore sizes: ¾, 1 ½, and 2 inches
Rotary actuators are also allowed
Notes on Actuators
Force = Pressure x Area
Area= pi x squared radius
radius = diameter (bore) / 2
Retracting force is less than extending force
Flow Rate Valve
Control the flow
Simply a fitting that widen or narrows the
flow path of the air
Used to slow the air movement, thus slowing
mechanical movement
Does not take away from the net force.
Must be adjusted manually
Aashish Sreendharan presents…
Motors - CIM
Used to drive robot
Motors – Van Door
Powers doors on minivans
Motors – Fisher Price Motors
Used on Fisher Price
Toys
Made by Johnson
Electric or Mabuchi.
Power Distribution Diagram
Power Distribution Explained
Battery (12V, Lead-Acid Battery)
Main Circuit Breaker
Power Distribution Block
Components:
Victors (ESC)
Spikes
Controller
Power Distribution Picture
Spikes Relays
Control direction.
Two single pole,
double throw relays.
Forward = 12V to
M+ and M- grounded.
Reverse = 12V to Mand M+ grounded.
Neutral = M+ and Mgrounded, or 12V
applied.
H-Bridge.
H - Bridge
4 Switches.
Combination of
switches on to drive
motor.
Electronic Speed Controllers
Known as: Victors.
Use Victor 884's.
Control speed and
direction.
Uses PWM.
Pulse Width Modulation
Two Types:
Power Delivery
Control Signal
David Liu presents…
Pulse Width Modulation
Two types
Power transfer
○ Between speed controller and motor
Signaling
○ Between controller and speed controller
Potentiometers (Pots)
Sensor for measuring position:
Rotation, distance, etc.
Potentiometers
Simplest type:
Slider
Slider is connected
to output.
+5V
Acts as a
Voltage Divider
+5V
+5V
Output
10 KΩ
GND
GND
5V
4.2V
3.3V
2.5V
3 KΩ
9
0V
7 KΩ
1
3.5V
0.5V
GND
Reading the Value
Analog voltage level
Analog-to-Digital Converter (ADC)
Converts to number
0-1023 for 10-bit ADC
Pots: Uses
Sense position: e.g. lift
How to sense the lift
position?
Travel length is 6 feet
No linear pot long enough
Rotary Pots
Pots
Multi-turn pot:
Screw with wiper resting on threads
Usually 3, 5, or 10 turns
Alignment is important!
Continuous rotation: use encoder
Optical Encoders
to controller
Optical
Sensor
to controller
Optical Encoders
to controller
to controller
Optical Encoders
Determining Distance Travelled
Count pulses
Example:
○ Given: Encoder stripes = 128
○ Given: Wheel diameter = 6”
○ Given: counted 85 pulses
1 revolution 6 inches
85 pulses
128 pulses 1 revolution
= 12.52 inches
Optical Encoders
Determining Speed
A. Count pulses per interval
○ Example: in 1 second, 256 pulses.
Speed = 2 revolutions/second
○ Inaccurate and slow
○ Analogy: On a bicycle
Mark the wheel
Count passes in a minute
Optical Encoders
Determining Speed
B. Measure time between pulses
○ Example: time between two pulses = 3.9ms
1 pulse 1 revolution 1000 ms
2 rev/sec
1 sec
3.9 ms 128 pulses
○ Only requires observing two consecutive pulses
Ultrasonic Sensors
Determine distance
Send pulse of sound
Measure time until echo
Johnathan Chai presents…
Required Capabilities
Speed
Point-to-point Movement
Turning in place
Controllable
Skid/Tank Steering
Power left and right sides independently
Joystick control
Ackerman Steering
Limited turning due to geometry
Team 34’s Design on Chief Delphi
4 Wheels
Fast but slides on ground when turning
Wide vs. Long base
6 Wheels
Center wheels dropped about a quarter inch
“Rock” on center when turning
Swerve Drive
Maneuverability
Time costs
Craig Hickman’s Design on Chief Delphi
Wheels
Rubber
Roughtop
Mecanum
Omni-wheels
Tank Treads
AndyMark Wheels
Conclusion
Covered major components of FIRST robots
Slides available at lynbrookrobotics.com
Tech > Resources > “WRRF Presentations”