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Locomotion
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Purpose
The following exercises will familiarize you with locomotion and odometry. Please refer to chapters 5 and 6 of "The Robotics Primer".
Overview
Most mobile robots have a set of motors attached to wheels for movement. These motors generally contain wheel encoders to provide the robot with information about how far and in what direction it has traveled. This data allows the robot to estimate where it is (pose estimate). These encoders count the number of motor rotations, and with a little math this count can be converted into a distance traveled. However, mechanical systems are not perfect. Wheels slip which cause miss calculations, and different terrain may exacerbate this problem. In general measuring odometry through dead-reckoning accumulates error over time. These exercises will demonstrate this.
Hardware
| Exercise | Command Module | Gumstix | Misc |
|---|---|---|---|
| Exercise 1 | Yes | Yes | N/A |
| Exercise 2 | Yes | Yes | Light Sensor |
| Exercise 3 | Yes | Yes | Light Sensor |
| Exercise 4 | No | Yes | N/A |
| Exercise 5 | Yes | Yes | N/A |
Exercise1 Locomotion and Odometry
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Let's begin with a simple exercise that will demonstrate how to move the Create. Once you complete this exercise you should understand the code necessary to control the wheel motors, and the problems with raw odometry for pose estimation. For the first couple exercises, we will walk through and explain all the steps. The later exercises will assume that you are more familiar with writing code for the Create. |
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Exercise2: Path Following
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For this exercise we will study a different method of locomtion. Instead of using odometry, we will use light sensors (photoresistors) to follow a path. Photoresistors have the property of changing their resistance with different light intensities. Therefore a dark line on a light colored floor should be detectable. The basic principle for this exercise is to construct an assembly to hold the photoresitors, use the photoresistors to detect and follow a dark line. |
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Exercise3: Homing
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We will now look a type of locomotion called homing. This type of locomotion involves placing a beacon in the environment which the robot can easily sense. The goal of the robot is to move towards this beacon, and stop just before it. There usually is no fixed path the robot should follow, as in the two previous exercises. We will use a light sensor as the beacon, and two photoresistors as the primary sensors. |
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Exercise4: Teleoperation
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A fourth type of locomotion removes all the autonomy from the robot and places a human in control. For this exercise, you will manually move the robot in different patterns. The purpose is to demonstrate the challenges with teleoperation. |
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Exercise5: Holonomic and Non-Holonomic Control
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Now that we have worked through a few examples of how to acheive locomotion, let's take a closer look at exactly how a robot moves. We will constrain this exercise to wheeled robots. |
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