4 - Robot Control

Question 1

What do movement commands depend on?

Answer 1

The wheel configuration

Question 2

Name 2 wheel configurations

Answer 2

Omni-directional (Rovio) and differential drive (Turtlebot/Roomba)

Question 3

What is the question when it comes to moving robots?

Answer 3

What speeds to turn each wheel to move in a desired direction

Question 4

What are the 3 parts to motion control?

Answer 4

Model, algorithm and engineering

Question 5

What is the ad-hoc model?

Answer 5

Calculating the number of steps required to perform a distance unit

Question 6

What does the number of steps required to perform a distance unit depend on?

Answer 6

Different for each speed value, and other factors such as surface type

Question 7

What is the formula for a wheel?

Answer 7

c = 2nr

Question 8

How do you calculate spinning at 60 degrees per second into radiants?

Answer 8

ω = (60 / 360) * 2n
v = r ω

Question 9

How do you calculate it with 2 wheels?

Answer 9

v = 1/2 r (ωl + ωr)

Question 10

How do you calculate one wheel going forward?

Answer 10

Forward Model: v = r ω

Inverse Model: ω = v/r

Question 11

How do you control an omni-directional wheel configuration such as a Rovio?

Answer 11

Which speeds to turn each wheel to move in a desired direction

Question 12

Discuss the Rovio wheels

Answer 12

Universal wheels/omni wheel

Simple design, significant slippage and can be improved by the Mecanum wheel

Question 13

How do you calculate the straight line for an omni-directional wheel?

Answer 13

ωr/cos(a)

Question 14

How do you calculate the rotation for an omni-directional wheel?

Answer 14

ωr/1

Question 15

What is an open loop controller?

Answer 15

Generates a control signal so that the robot’s position is equal to the desired position

Question 16

What are the disadvantages to open loop controller?

Answer 16

No measurements and no feedback

Can rely only on the model

No possibility of correcting the errors as they are unknown and how to deal with unexpected events, changes and obstacles?

Question 17

What is a closed loop controller?

Answer 17

Generates control signals that will keep the error e as small as possible

Question 18

What are the steps in a closed loop controller?

Answer 18

Issue DriveForward command u

Read the odometry and accumulate the total distance travelled

Stop if the total distance is greater than the specified value

Question 19

What is a bang-bang controller?

Answer 19

Where the control input depends only on the sign of the error, uses a constant value

Question 20

What is a proportional controller?

Answer 20

Changes ω proportionally to the error value

u = e*Kp

Kp = proportional gain

Question 21

What are the advantages to using a proportional controller?

Answer 21

Smoother actions and smaller errors

Question 22

What is the optimal Kp value for a proportional controller?

Answer 22

Where it has smooth behaviour and is robust to changes

Question 23

What is a vision-based controller?

Answer 23

Uses an object state (x pos and size) and calculates the difference between the desired and current state to adjust the control input u

Question 24

What is the PID controller?

Answer 24

Proportional, Integral and Differential

Question 25

What is the P is PID?

Answer 25

Proportional, it corrects the actual error

Question 26

What is the I in PID?

Answer 26

Integral, it accumulates the rate of change

Question 27

What is the D in PID?

Answer 27

Differential, it slows the rate of change and reduces overshooting

Question 28

What do we want to minimise in optimal control theory?

Answer 28

Errors, energy, response time

Question 29

What is the complete forward model?

Answer 29

V = 1/2 r (ωl + ωr)
A = 1/d r (ωl - ωr)

Question 30

What is the complete inverse model?

Answer 30

ωl = (v + (d * a) / 2) / r
ωr = (v - (d * a) / 2) / r