8.9: Arm Design

Students should revisit the arm design problem from the end of Unit 7.  Designers should create a single motor, gearbox, and arm system that can lift the weight of a single game object - the manipulator from Unit 6.  Designers must choose an arm length appropriate for the game, which fits within the 18” robot size requirement.  The gear ratio should be calculated so that the motor can be loaded such that it draws no more than one amp of current.  After calculating the necessary ratio, users must design a compound gearbox that achieves this ratio, and then calculate the final speed of the arm.


Mechanical power transmission systems are very important in the design and construction of competition robots.  A designer’s ability to vary the gear ratio and the mechanical advantage in a system gives them the versatility necessary to accomplish whatever work needs to be done, with whatever motors they have (at the expense of speed.)  At the simplest level, designers just need to determine their inputs and outputs, calculate the difference between them, and set their gear ratio accordingly.  This simple method can be applied to any number of motor/gearing systems.