Designing the Smart Cart

Combining physics and engineeringThe design of the Smart Cart provides a good example of physics and engineering together. A tool to help study the fundamentals of physics and mechanics, the Smart Cart underwent several iterations and engineering cycles before being ready for classroom use.
While there were many aspects to the Smart Cart design, the primary focus was to build a cart that could roll with virtually zero friction, measure forces applied to it, and simultaneously measure its motion, both linear and rotational; All while working without the use of cords.
The Smart Cart measures its one-dimensional motion using an optical encoder system. This system detects rotation in the cart’s wheels by measuring light reflected from an encoder wheel attached to the axle. Because the encoder system is accurate, very lightweight, and completely frictionless, it was a perfect tool for the Smart Cart to measure motion in one-dimension.
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On the Smart Cart’s encoder wheel are bands of reflective and non-reflective surfaces. Next to the encoder wheel is a light emitter and detector system. As the cart’s axle spins, light from the emitter reflects only from the reflective bands on the encoder wheel and hits an array of detectors. This light appears to the detectors as tiny flashes as the encoder wheel spins. These flashes are converted to digital signals, or “states,” and sent to the cart’s on-board computer, each state change representing the smallest measurable rotation in the encoder wheel. Depending on the order and number of the state changes, the cart’s computer can determine if it is moving forward or backward, and the distance the cart has traveled.
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