Base FundamentalsBase FundamentalsBeach Cities Robotics – Team 294Beach Cities Robotics – Team 294

Andrew KeisicAndrew Keisic

June 2008June 2008

2 - Introduction / Agenda

Sources

Copioli and Patton’s “Robot Drive Systems Fundamentals” presentation

Topics

3 - Introduction / Agenda

Center of Gravity

Types of Drive Trains

Maximizing Design

Motor Performance

Gear Ratio Calculation

Center of Gravity

A point in space where gravity acts

Why it’s important?

Determines the balance and stability of an object

Center of Gravity

Stability - what ball is the most stable? the least?

Center of Gravity

What robot is the most stable? The least?

How do you know?

What systems are inherently stable?

Center of Gravity

Putting math behind intuition

Stability Triangle

h

b2b1

α1

α2

h

b111 tan

h

b212 tan

Center of Gravity

Limit of stability is determined by the CG location

In other words – the maximum ramp

angle of a stationary robot

h

b2122 tan

h

b1111 tan

β1β2

α1

α2

Center of Gravity

Why keep it low?

Lowering the center of gravity maximizes alpha!

Stability Triangle

h

b2b1

α1

α2

Center of Gravity

BCR 2008 FRC initial CG estimate

Type of Bases

Type of Bases

Drive train configurations

simplerear wheel drive

simplefront wheel drive

simpleall wheel drive

simplecenter drive

6 wheeldrive

tracked drive There is no “right” answer!

swerve/ crab drive other?

Types of Bases

simplerear wheel drive

Type of Bases

simplefront wheel drive

Types of Bases

simpleall wheel drive

Type of Bases

simplecenter drive

Types of Bases

6 wheeldrive

Types of Bases

tracked drive

swerve/ crab drive

other?

Maximizing Design

Designing is all about tradeoffs

Speed vs torque

Low CG vs reaching high

Weight vs features

Control vs power

Maximizing Design: Motor Performance

Maximizing Design: Motor Performance

Maximizing Design

Requirements

Before designing a system, we must know what it needs to do

The design requirements usually stem from the game

Strategy plays a big part in the requirements

Decide the requirements as a team

For competitive robots, torque is always needed

We’re going to design for maximum torque – pushing ability

weightfront

The normal force is the force that the wheels exert on the floor, and is equal and opposite to the force the floor exerts on the wheels. In the simplest case, this is dependent on the weight of the robot. The normal force is divided among the robot features in contact with the ground.

normalforce(rear)

normalforce(front)

Note: Slide from Copiloi & Patton presentation

Traction Fundamentals: “Normal Force”

Traction Fundamentals

The friction coefficient for any given contact with the floor, multiplied by the normal force, equals the maximum tractive force can be applied at the contact area.

Tractive force is important! It’s what moves the robot.

normalforce

tractiveforce

torqueturning the

wheel

maximumtractive

force

normalforce

frictioncoefficient= x

weight

Note: Slide from Copiloi & Patton presentation