# Constraining Motion ## Constraining Motion Basics Robots need movement to accomplish goals; arms must pivot, wheels must turn, etc. However, movement that isn’t directly related to those actions can affect the accuracy and precision of the robot mechanisms. This unintended motion must be properly restricted, or **constrained**. Long and thin structures can flex and deform, making it difficult to interact with objects and operate in a repeatable manner. Make use of brackets and additional extrusion or c-channel to strengthen and constrain these structures. ## How to Constrain Motion Gears and sprockets must stay aligned or else they won’t work properly. For example, if two sprockets are not perfectly aligned with each other, the chain between them will run off the sprockets. Keeping parts aligned on a shaft, and keeping the shaft itself from sliding out, is critical for reliably working robot mechanisms. Use a combination of spacers and shaft collars to align and constrain these parts into place.

At the top of the image is a shaft with two sprockets perfectly aligned and connected by chain. Underneath is another image of a shaft with unaligned sprockets, causing the chain to be unaligned and run off the sprockets.

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