Friday, October 14, 2005

Flex Sensor Accelerometer?!?

This prototype is an attempt to sense the movement of a ping pong paddle being swung—not only the paddle’s movement , but also the difference in the velocity of the swing.

The prototype works on the idea of inertia—the tendency of a body at rest is to remain at rest. As the paddle swings forward (green arrow) the weight will want to stay in its resting position. As the paddle moves away from the weight, the plastic strip will start to bend given the resistance of the weight’s inertia (blue arrow.) Bending the strip bends the attached Flex sensor, which in turn changes the resistance to the voltage passing through it. The faster the swing, the more the strip bends, the more resistance is generated.

To make the prototype I used a Flex sensor, some thin sheet plastic (in this case, styrene), a bolt and nut, wire, a little tape, and some wood screws.

First, I cut the plastic into a thin strip with a wider tab on one end. I then drilled a hole in the thin end to pass the bolt through, and two more holes down at the tab end for the wood screws. I put a bolt through its corresponding hole and threaded it on the nut. The bolt and nut will act as a weight in the system. After that, I secured the Flex sensor to the plastic strip (just beneath the bolt) with a little clear tape. I then laid the strip against the flat part of the paddle (Flex sensor side facing the paddle) and lined up the tab to the paddle’s handle. The plastic strip was attached to the handle with the wood screws. I secured the wires with a bit of electrical tape, just to clean up the appearance and to protect the contacts on the sensor from any potential abuse.


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