Unit 3 - Gear Ratios and Arm Design

Unit Objectives

This unit teaches students about manipulators and accumulators that can be used on a VEX robot. These are mechanisms that help the robot interact with the environment. It will also introduce the concept of gear reduction as it applies to manipulators so that the students can design a robot arm that can hold up a certain weight at a given distance.

Unit Teacher Notes

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Lesson 3.1 (60 minutes)

This lesson will teach students about the different types of lifting mechanisms and accumulators. It will also explain how a gear reduction can be applied to increase the output torque of your motor.


  • Identify the different types and categories of robot manipulators, accumulators, and lift designs
  • The students will be able to differentiate three degrees of freedom

Lesson 3.2 (120 minutes)

In this lesson, students will learn how the provided motor specs for the 393 motor are limited by power draw. Students will then combine this knowledge to calculate the appropriate gear reduction necessary to lift an arm given motor limitations.


  • Explain the difference between speed, power and torque and demonstrate manipulations of these concepts as it relates to manipulators
  • Demonstrate the correct use of the calculations needed to choose a gear reduction for the torque of a robot arm.

Lesson 3.3 (540 minutes)

Students will apply the concepts learned in the previous two lessons to create a robot with an arm that can lift a heavy object.


  • Analyze the features of their robot and identify/synthesize how to change them to get different results
  • Calculate the output torque of their arm based on their design and the limitations of the motor including a safety factor.

Quiz (30-60 minutes)

Quiz on the unit


  • Check for Understanding