Mobile Robotics Exam 1

Mobile robot.

1. Any robot that posses mobility w.r.t a medium.

2. Any system that is:

-Mobile

-Somewhat autonomous

-Intelligent

Taxonomy of mobile robots

1. Terrainability

2. Locomotion type

3. Steering Type

4. Body compliance

5. Shape

6. General class

-consumer

-defense

-research

7. Medium of transportation

8. Level of autonomy

Define proprioceptive sensor

Measure internal values to the robot.

Passive Sensor

Measure ambient values.

Active Sensor

Emits energy and measures environmental reaction

Define exteroceptive sensor

Measure external values to the robot.

3 Basic questions addressed in mobile robotics

1. Where am I?

2. Where am I going?

3. How do I get there?

Type of wheels and DOF

a) standard wheel - 2DOF

b) caster wheel - 3 DOF

c) Swedish Wheel - 3 DOF

Wheel Configurations

3 Wheels:

-differentially steered

-Steered standard wheel

4 Wheels:

-Ackerman steered

-Skid Steer

-Four wheel steering

Forward Kinematics

Given joint velocities find robot velocities

Inverse Kinematics

Given robot velocities find joint velocities.

Static characteristics of a sensor

Have to do with steady state behavior. Include accuracy, precision, sensitivity etc.

Dynamic characteristics of a sensor

Measures behavior between the time measured and the time steady state is obtained. Includes bandwith and frequency.

Know how encoders work. Know how to do calculations involving encoders.

Encoders measure angular position. Velocity is then estimated from this value. Optical pulses are generated onto the shaft of the motor. The angular position is proportional to the number of pulses.

Quadrature for an optical encoder

Has 4 states. Multiply PPR by 4. A 500 PPR encoder becomes 2000 PPR. PPR is pulses per rotation.

Single ended V.S differential encoders

In single 2 channels are used. In differential at least 4 are used.

Accelerometer

Measures specific force. Also measures inclination and vibration.

Gyroscope

Measure rotational motion in degrees or revolutions per second.

How are accelerometers and gyroscopes used in conjunction to perform inertial navigation?

Accelerometer obtains velocity and position, Gyros track orientation. GPS is also used.

What are the challenges of ultrasonic sensors?

1. Position of detected object unknown

2. Specular reflection

3. Picks up signals from other sensors (crosstalk)

4. Air temperature changes cause error

How to compute a fix in GPS navigation?

If the GPS receiver cas see at least 4 satellites its position in time can be accurately calculated.

How to compute vehicle altitude using GPS?

Knowing the exact distance to the ground receiver from the satellites allows for calculation of altitude.

Know the challenges of GPS

1. Time sync between individual satellites and GPS receivers.

2. Precise real-time location of satellite position.

3. Accurate ranging from the satellites to the receiver.

How does differential GPS work?

2 GPS close to each other will have the same error so the error can be corrected.