Unit 6 Part 1 INTRODUCTION TO ROBOTICS Part

Robot Systems • Structural System • Physical system that provides support and stability • Propulsion System (motion) • Drive system includes motors, wheels, and gears • Control System • Microcontroller, operating program, electrical power, and joystick • Tool and Actuator system • Arms, grippers, manipulators • Sensor and feedback system • Perception, transducers Copyright © Texas Education Agency, 2012. All rights reserved.

Structural System • The structural subsystem of the robot is responsible for physical support. • Holds everything in place • Also provides physical protection • The durable “skeleton” of the robot to which all the other subsystems are attached • The Structure and Motion subsystems are tightly integrated to form the chassis of the robot. Copyright © Texas Education Agency, 2012. All rights reserved. Photo Credit: VEX Robotics, Inc.

Before You Begin • Many types of tools and parts are necessary. • Some tools and parts are required, others are simply nice to have. • The larger the variety of supplies, the more creative the design can be. • Systems can look better and be more • structurally sound. Also increases the need for a tool/part inventory and management system. Copyright © Texas Education Agency, 2012. All rights reserved.

Recommended Tools • Allen wrench set (also called an L-wrench) • Open ended wrench • Screwdrivers • Flat head and Phillips Photo Credit: VEX Robotics, Inc. • Needle nose pliers and diagonal cutters • Wire strippers • Crescent wrench Copyright © Texas Education Agency, 2012. All rights reserved.

Additional Tools • Drill and drill bit set • Saws for metal, wood, and plastic • Examples: • Hacksaw, band saw, chop saw, scroll saw • A variety of screws, nuts, bolts • Vise • Multi-purpose rotary power tool to cut and smooth metal • Wire, soldering iron, electrical connectors Copyright © Texas Education Agency, 2012. All rights reserved.

Example Parts • Types of bolts • 6 -32 and 8 -32 • Keps nuts • Square drive shaft • Bearing flat Photos Credit: VEX Robotics, Inc. • Spacers and friction reducers • Metal sized by number of holes 5 X 15 1 X 25 Copyright © Texas Education Agency, 2012. All rights reserved.

Photos Credit: VEX Robotics, Inc. Copyright © Texas Education Agency, 2012. All rights reserved.

The Robot Base • The platform or base determines the stability, the durability, the maneuverability, and the functionality of the robot. • Usually made from wood or metal • Provides the support structure for the rest of the robot • Everything connects and mounts here • The frame or skeleton Copyright © Texas Education Agency, 2012. All rights reserved.

Robot Stability • Stability is defined as when the center of gravity is over the points of support for the base (called the support polygon). • To increase stability, lower the center of gravity. • Long arms need additional support. • With one point of support an arm will rotate. • If the center of gravity is moved outside the support polygon the robot will tip over. Copyright © Texas Education Agency, 2012. All rights reserved.

Base Material Considerations • Common materials are wood, aluminum, sheet metal, or plastic (HDPE). • Consider both weight and strength. • Metals have a high strength to weight ratio. • Some plastics like plexiglass will crack or break when cut and drilled. • Sheet metal and aluminum conduct electricity. • Wood can splinter or split but is cheap. Copyright © Texas Education Agency, 2012. All rights reserved.

Base Material Considerations • Angled metal in an L or C shape will retain its shape under load. • A solid square or round tube makes a very strong support structure. • Can be metal or PVC – be creative! • Wood is great when load is not too great. • Wood can flex, bend, or break. • Works well for a superstructure or platform. Copyright © Texas Education Agency, 2012. All rights reserved.

Base Material Considerations • Even if you use wood or plastic for the base, you will need to use and cut metal. • Motor mounts can be made from metal bent to a 90 degree angle (like angle iron). • Wheels are an assembly with a mounting hub adapter to connect motor shaft to the wheel. • 2 types of adapters: set screw and collet type • Other types include keyway and D hubs. • These are usually for larger shafts. Copyright © Texas Education Agency, 2012. All rights reserved.

Wheels • Two drive wheels make control easier. • Can be controlled with a single joystick • The robot turning point will be between the two drive wheels. • Large turn radius • Non-drive wheels will have to slide or slip • Four drive wheels move the pivot point into the center of the robot. • Robot will turn in place. • May require an additional joystick. Copyright © Texas Education Agency, 2012. All rights reserved. Pivot Point

Wheel Support • Wheel axles should be supported at two points by the chassis or frame. • Usually on each side of a wheel as shown Bearing or hub Frame Wheel Axle • Needed to keep the wheel straight and the axle from bending Copyright © Texas Education Agency, 2012. All rights reserved.

Types of Propulsion Systems • Legs • Motors, wheels, bearings • Tank treads • Gears and belts • Supported by the structural system • Includes mounting hardware • Servos are used to hold a position, and are generally considered part of a system designed to complete specific objectives. Copyright © Texas Education Agency, 2012. All rights reserved.

Movement • Wheels and pulleys use DC motors. • A DC motor continuously rotates (360⁰). • Speed is controlled by the amount of DC voltage. • Direction is controlled by polarity of DC voltage. • Arms and grippers can use servos. • A servo goes to a position and holds there. • Typically minus 90 degrees to plus 90 degrees • Position is controlled by an electronic signal. • Different forms of pulse width modulation are used for each (motors vs. servos). Copyright © Texas Education Agency, 2012. All rights reserved.

DC Motor Control Signals • Voltage amount given by pulse width modulation • Longer “on” time means • higher voltage Higher voltage equals higher motor speed • Direction of rotation controlled by polarity Copyright © Texas Education Agency, 2012. All rights reserved.

Servo Control Signals • Pulses are always 20 ms apart • • • 50 pulses per second Pulse width varies between 1 and 2 ms • 18 -19 ms of “dead time” • A DC motor getting this signal would spin very slowly The pulse width determines the servo position • 1. 5 ms = middle (or null) • 1 ms = full ccw (usually - 90⁰) • 2 ms = full cw (usually + 90⁰) Copyright © Texas Education Agency, 2012. All rights reserved.

Kit Versus Build From Scratch • You can choose to build your robot completely from scratch using common and cheap parts. • The advantage of a kit is that you get all of the parts you need. • The parts are designed to work together. • There are standard designs and construction • techniques. There is usually some help in the form of instructions and forums, plus corporate technical assistance. Copyright © Texas Education Agency, 2012. All rights reserved.

Kit Versus Build From Scratch • If you choose to build from scratch you have lots of freedom for design and construction, but you need a large variety of parts. • Although there are many different kinds of motors, brushed DC motors are popular because of cost and reliability. • The motion and structural system must be designed to work together. • Functions are different but they are integrated to form the chassis. Copyright © Texas Education Agency, 2012. All rights reserved.