Roberto - Balancing Robot

RIT Computer Engineering Senior Design Project

Group Members

 Jeff Mahmood  Paul Krausman  Dave Froman

Project Description

 Two-wheel balancing robot – Balances on any angled surface – Remains balances indefinitely   Remote controlled “Inverted Pendulum”  PID Controller

Physical Layout

Tilt & Rate Sensors HC12 18.0" RF Receiver H-Bridge Battery 10.0"

PID Algorithm

 Means to control some output from a combination of different factors  Differential equations solved in the frequency domain  We will solve experimentally

PID Algorithm (cont.)

 PID is “Proportional Integral Derivative”  Output based on the aggravate of 3 factors – Error – Error Derivative – Error Integral  PID algorithm combines these 3 factors to determine appropriate output

Error Definition

Actual Error Set Point  Error: Difference between set point and actual  Error can be positive or negative

PID Equation

  Proportional Integral Derivative Output = P* Θ + I*Θ + D*Θ’ – – – P is the Proportional constant  Current error I is Integral constant  Sum of past errors D is Derivative constant  Rate of change of error

Proportional

40° Θ 0°  Torque applied to motors is proportional to amount of error

Integral

 Sum of all errors over time  Biases output so all errors cancel over time

Derivative

300°/sec 0°  Torque applied to motors proportional to derivative of error  Velocity of error

Tuning PID Controllers

 Goal: – – Find coefficients for P, I, and D terms Robot should “snap” back to set point after any disturbances – Prevent any oscillations – Robot should remain at set point indefinitely

Finding P Term

 Set I and D terms to 0  Set P term to 1  Increase P term until strong oscillations occur  Some references recommend setting P to 60% of this value

Finding D Term

 Slowly increase D until oscillations begin to slow  Fine-tune D – – – Robot will oscillate if D is too high Robot will fall over is D is too low Robot should “snap” back to set point after any disturbances

Finding I Term

 More difficult than P and D  Generally inverse of D  Limit sum to prevent saturation  Sliding window

Increase Performance

 Robot may seem sluggish – If either P or D is set too low, robot will be slow to respond  Robot may oscillate – If either P or D is set too high, robot will oscillate before settling on set point  Tweak P and D terms until optimal performance is achieved

Sensors

 Accelerometer – Measures tilt (proportional error) – – Slow response, but accurate Gives sense of “up”  Gyro – Measures velocity (derivative error) – – Fast response, but inaccurate Suffers from drift over time

User Interface - Remote Control

  Two axis control – left and right motors 2 commands for each side – move forward, back  Uses 4 bit encoding/decoding(8 values used)  Each switch press has unique encode value, which is transmitted and received

Remote Control

 Momentary rocker switches are used for intuitive remote controlled car feel  Robot moves by pressing both switches in the same direction, turns by alternating directions

The End

 Questions???