The overall
vision is to have two 25
foot long (7.5m) pendulums that naturally
swing from the ceiling of the theater. At the end of each pendulums there will be an RGBW
LED rigged within a focusing mini flashlight.
Building these pendulums as well as all of the wiring for the
LED is easy and already complete. The
LED will be controllable with a
DMX controller. Now comes the tricky part for us. We would like to be able to control the swaying movements with the same
DMX controller.
As of now we have 2 ideas for the swaying mechanism.
Idea 1: Linear actuator. If we use a liner actuator we will mount a hinge onto its carriage. By controlling the actuator back and forth at a rate just ahead of the frequency of the pendulum we will be able to naturally
swing it back and forth gradually building up momentum or slowing it down. We want it to be in sync with the lighting, so it would have to be able to accept
DMX signal.
Idea 2: Stepper motor. With the stepper motor only we would mount a 3' (1m) arm onto the motor shaft. On the end of the arm we would attach a hinge. By controlling the stepper motor back and forth at a rate just ahead of the frequency of the pendulum we will be able to naturally
swing it back and forth gradually building up momentum or slowing it down. We want it to be in sync with the lighting, so it would have to be able to accept
DMX signal. The stepper motor in this instance would need more torque than the linear actuator motor because it will have more leverage against its position. However, we are not sure how to go about identifying how much
power our motor needs.
The pendulum will probably weigh no more than 10 lbs. If we go with a linear actuator it does not need much strength. We have calculated that the frequency at 25 ft. (7.5m) of the pendulum will take approximately 5 seconds to complete its journey from starting
point back to starting
point, therefore we will need a linear actuator to be fast enough to travel its stroke length in 2.5 seconds. We assume that we will need 6-12 inches of stroke length to provide the pendulum sway we are looking for. So we are looking at an approximate speed of 5in./sec. (127mm/sec.)
With both options we will want to be able to control the speed and frequency with our choreographed
DMX program. This is a one time use so at this
point we are looking for a
system that is very affordable. We found individual
DMX relay boards that communicate between
DMX controller and motor, but they are like $300 each and we need one for each pendulum, and that doesn't even include hardware cost. We are looking for a complete solution for the mechanism and
relay that costs hopefully less than $750 maybe more like $500 for both pendulums.