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”