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Base Fundamentals Beach Cities Robotics – Team 294 Andrew Keisic June 2008

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2 - Introduction / Agenda Sources Copioli and Patton’s “Robot Drive Systems Fundamentals” presentation

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Topics 3 - Introduction / Agenda Center of Gravity Types of Drive Trains Maximizing Design Motor Performance Gear Ratio Calculation

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Center of Gravity A point in space where gravity acts Why it’s important? Determines the balance and stability of an object

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Center of Gravity Stability - what ball is the most stable? the least?

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Center of Gravity What robot is the most stable? The least? How do you know? What systems are inherently stable?

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Center of Gravity Putting math behind intuition Stability Triangle h b2b2 b1b1 α1α1 α2α2

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Center of Gravity Limit of stability is determined by the CG location In other words – the maximum ramp angle of a stationary robot β1β1 β2β2 α1α1 α2α2

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Center of Gravity Why keep it low? Lowering the center of gravity maximizes alpha! Stability Triangle h b2b2 b1b1 α1α1 α2α2

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Center of Gravity BCR 2008 FRC initial CG estimate

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Type of Bases

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Drive train configurations simple rear wheel drive simple front wheel drive simple all wheel drive simple center drive 6 wheel drive tracked drive There is no “right” answer! swerve/ crab drive other?

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Types of Bases simple rear wheel drive

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Type of Bases simple front wheel drive

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Types of Bases simple all wheel drive

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Type of Bases simple center drive

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Types of Bases 6 wheel drive

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Types of Bases tracked drive

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swerve/ crab drive

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other?

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Maximizing Design Designing is all about tradeoffs Speed vs torque Low CG vs reaching high Weight vs features Control vs power

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Maximizing Design: Motor Performance

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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

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weight front 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. normal force (rear) normal force (front) Note: Slide from Copiloi & Patton presentation Traction Fundamentals: “Normal Force”

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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. normal force tractive force torque turning the wheel maximum tractive force normal force friction coefficient = x weight Note: Slide from Copiloi & Patton presentation

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