5.1 Introduction to Motion Feedback

In robotics, simply commanding a robot to move is not enough. For accurate and reliable operation, the robot must be able to measure its own movement. This is known as motion feedback. Without feedback:

• Movement is based on time (less accurate)
• The robot cannot detect errors
• Positioning becomes unreliable

With feedback:

• Movement is measured in real time
• Errors can be corrected
• Precision is significantly improved

Motion feedback is essential for:

• Autonomous navigation
• Distance control
• Speed regulation

5.2 What is an Encoder?

An encoder is a sensor used to measure rotation. It is typically attached to a motor shaft or wheel. As the motor rotates, the encoder generates signals that can be counted and converted into:

• Distance
• Speed
• Position
• Encoders allow the robot to understand how far it has moved and how fast it is

moving.

5.3 Types of Encoders

1. Incremental Encoders

• Measure relative movement
• Count pulses as the shaft rotates
• Most commonly used in robotics
• They do not store position when powered off.

2. Absolute Encoders

• Provide exact position at all times
• Maintain position even after power loss
• Used in more advanced and industrial systems.

5.4 How Encoders Work

• Encoders generate pulses as the motor rotates.
• Each pulse represents a small amount of rotation
• The controller counts these pulses
• The total count is used to calculate movement

Example: If one full wheel rotation produces 100 pulses:

• 100 pulses = 1 rotation
• 50 pulses = half a rotation

This allows precise measurement of movement.

5.5 Measuring Distance Using Encoders

Encoders can be used to calculate how far a robot has travelled. To do this, the system must know:

• The number of pulses per rotation
• The circumference of the wheel

Concept: Distance traveled = number of rotations × wheel circumference This allows the robot to move:

• A specific distance
• With high accuracy

5.6 Measuring Speed

Encoders can also be used to measure speed. This is done by:

• Counting pulses over time
• Calculating how quickly the motor is rotating

This allows:

• Speed monitoring
• Smooth acceleration
• Controlled deceleration

5.7 Why Feedback is Important

Without encoders, robots rely on open-loop control, meaning they assume movement happens as expected. This leads to:

• Inconsistent results
• Drift and inaccuracy
• Poor autonomous performance

With encoders, robots use closed-loop control, meaning they continuously adjust based on actual movement. This results in:

• High accuracy
• Reliable performance
• Better control

5.8 Encoders in Drivetrain Systems

Encoders are commonly used in drivetrain systems to:

• Track distance traveled
• Maintain straight movement
• Improve turning accuracy

Example: If one side of the robot moves faster than the other:

• The robot will drift
• Encoders can detect this and allow corrections.

5.9 Common Encoder Challenges

1. Incorrect Calibration

If the distance per pulse is incorrect:

• Distance calculations will be wrong

2. Noise and Interference

• Electrical noise can cause incorrect readings.

3. Slippage

If wheels slip:

• The encoder may report movement that did not actually occur

4. Misalignment

• Improper mounting can lead to inaccurate readings.

5.10 Improving Accuracy

To improve encoder accuracy:

• Calibrate the system properly
• Use stable mounting
• Ensure proper wiring
• Combine with other sensors when needed

This leads to more reliable motion tracking.