spider


Posted on Feb 7, 2014

The spider prop is fairly simple in terms of mechanical setup. Where it gets somewhat complicated is in the electronics setup. It is based around a stepper motor. By their very nature, stepper motors are non-trivial to control. By that, I mean that you can`t just apply power and expect them to turn. They need a controller of some type, such as a


spider
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computer or a microcontroller. However, the advantage of a stepper motor is that the controller has a very high degree of control over the position of the motor`s shaft. By keeping track of the number of steps executed, the controller knows exactly how far the spider has been unwound, and so it knows exactly how many steps it needs to execute in the other direction to wind it back up. As I mentioned earlier, the mechanical set up is pretty basic. Attach a couple of L-brackets to the motor, and attach the motor to a small sheet of plywood. Drill a hole about the size of the motor shaft into the end of a dowel that is three inches long or so. The diameter of the dowel is up to you. The thicker the dowel, the faster the spider will wind and unwind. Glue the dowel onto the motor shaft. Drill a hole in the piece of plywood the motor is attached to. The hole should be directly under the dowel attached to the motor shaft. Run a string through the hole and attach it to the dowel. I stuck a thumbtack into the dowel and tied the string to that. Tie the other end of the string to the spider, or whatever else you want to go up and down. Now, for the electronics side. The stepper motor I use has 6 leads. Two of them are to supply power to the four coils within the motor. Each of the other four leads is connected to one of the four coils. By connecting each of the four leads to ground, one at a time, in the proper order, the motor shaft...




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