The idea for a drawbridge came from dinner with a non engineering major. While initially skeptical, we soon agreed that the idea was doable and, more importantly, interesting.
We will be constructing and programming a plywood drawbridge using Matlab. It will be capable of detecting motion through use of a photoelectric sensor and lifting the two halves of the bridge as a response. It will use servos to wind up strings attached to the ends of the halves to lift them.
- 4 servos
- duct tape
- metal rods
- photoelectric sensor
Our first design decision was how to raise the bridge, i.e. where exactly we would place the servos and in what configuration. Initially we planned to raise the bridge by attaching the servos to the bridge halves. Upon further consideration we decided upon a more indirect approach and implemented a drawbridge design where the servos would wind up strings attached to the end of the bridges. We figured that this design was more interesting and it would be easier for the servos to support the weight.
Additionally, we added an additioanl component by "robotizing" the bridge. We automated the bridge by triggering it with a light sensor. When an object blocked light from the sensor, the computer would recognize the dip in dispelled electrons and send a signal to the servos to turn and raise the bridge.
We began designing for construction by specifying rough dimensions of the bridge and of the individual parts. We decided that a 2.5 ft by 1 ft bridge was a substantial but convenient size to work with. From those dimensions we based the size of the rest of our parts. We had to take into account multiple considerations: 1. The height at which we suspended the servos, because it had to be tall enough to raise the bridge half (the half could not be significantly longer than the height of the pillars) and 2. The weight the bridge half would be, because that would affect the stability of the whole system.
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