Motorized control of lighting canopy

Community General Discussions
1

I would like to put together a motorized system for raising and lowering a lighting canopy for a saltwater reef tank. I was wondering if a forum member or administrator could give me a hand. Hopefully I’m in the right place.

This is the subject item than needs to be raised and lowered above the tank.

http://i116.photobucket.com/albums/o34/bilk22/Reef%20Tank/Reef%20Tank/image-11.jpeg

It weights approximately 50lbs. It needs to travel 15" - 20" in each direction and be mounted from the ceiling above the tank. I am guessing a linear actuator can be used for this, but would a stepping motor be suitable as well? If so, what would the specs be for that motor?

I have seen on the sales portion of the site, there are stepping motors with internal gearboxes. I’m sure pulleys would also be needed as part of the components.

Is anyone out there willing to help me design a workable idea and walk me thru it, delineating what components are necessary and how to wire the motor to a controller?

2

We can’t really help with the specific design, but there are generally two possible I would recommend.

The first is the simplest, but costs more. I would recommend designing a cable and pulley system that supports the canopy from all four corners, and then use an a single actuator to pull on all cables to make the canopy move up and down.

The following linear actuator only has a stroke of 12 inches, however it does have twice the strength needed so you can use another pulley on it in a way that it doubles the range of the cables at the expense of also doubling the load.

This actuator comes with its own digital motor controller, so you only need to generate the appropriate pulse width to make the motor move to the position you desire. This gives very good position reliability and control, good speed (about 1 in per second), and since it is a linear actuator, it does not consume any significant current when idle.

The second is less expensive, but is more complex. You can use steppers motors like you suggested, such as this one:

However, even this one, which is our strongest, has only 666 oz-in of torque. If you attach to it a (for example) 3 in diameter winch, it will only have about 25 lbs of linear force on the cables. In this case, you will need to use another pulley to double length of cable that needs to be pulled in order to divide the load in half. With a pulley like this in place, the canopy will move at a pretty slow pace, about 4-5 inches per minute.

Another possibility is to use two stepper motors that each pull half the total weight, which would then make the canopy move 8-9 inches per minute. However this does add the complexity of needing to ensure that your steppers remain synchronized.

If you like either of these options, let us know and we can recommend the other electronic components you will need to complete the circuit. For example, how will you be controlling the position? Simple “raised position” and “lowered position” buttons, or do you want something that is adjustable?

We hope this helps,