DIY Ecotech Radion LED Hanging Sytem
Follow along as I detail the design and contruction of an electronic light lift that will accompany my newly aquired Ecotech Radion LED lighting system. As with most projects here, this one will not likely save me any money, but it will be fun to design and construct.
Metal Halide Hanging System
The back story: When I contstructed my 75 gallon in-wall aquarium, I chose not to provide access panels on the front side. Due to the lack of access panels, stocking, feeding and maintenance can only be accompolished from the rear (fishroom) side of the aquarium. During their extended tunure over the aquarium, the Sunlight Supply ReefOptix III (no longer manufactured) metal halide pendants were situated just inches above the water, making maintenance and feeding a chore. To allow for more working space the pendants were bolted to a 3/4" square aluminum tube hung from a 4:1 block and tackle pulley system. The original design called for a motor driven pulley, but as is with many projects around here, it was never completed. When required, the lights were raised or lowered by hand as one would raise or lower a flag.
EcoTech Hanging System
While the Radion fixtures do have an acclimation feature and do, by design, sit higher above the water, they will still be in the way for some normal aquarium maintenance activities. My initial thought was to use the extremely well designed Ecotech Premium Hanging Kit and Rails. The included "Grip Lock" (brand name) adjuster that comes with the kit allows for height adjustments as needed. The downside is that this solution is better suited to initial adjustments for permantent height installations. Dynamic height adjustments would require me to adjust both sides of the light bar independently and would also require leaving extra slack on the hanging cables. The delimma brings me full circle to the initial metal halide hanging problem and project...
Block and Tackle Calculations
A block and tackle is used to gain mechanical advantage to lift a load. In general a 2:1 pulley system cuts the required force needed to lift a load in half at the expense of having to pull twice the rope for every inch the load is moved. In other words, to lift a 100 pound load 10 inches the working end of the rope would require 50 pounds of force and need to be pulled 20 inches. THe same logic can be applied to any ratio of pulley blocks. Certain configurations have been given common names (by the maritime and rigging trades) over the years. See the images below for a better understanding.
The ratios also work in reverse. If the block and tackle system is reversed, a small amount of movement can be used to move a load a large distance, as long as enough force is applied. In this case, the goal is to move a strong actuator a small distance to get the LED light bar to move a reletivley long distnace.
While I have not weighed the EcoTech Radion fixtures, they feel to be roughly 3 pounds each. The single 4' long light rail will support 3 or 4 fixtures with a maximum weight not likely to exceede ~16 pounds. If we add in a huge fudge factor for friction, pulleys and other hardware, the entire lifted mass will be far less than 50 pounds. A linear actuator capable of lifting 400 pounds could be used with a 4:1 block and tackle where each inch of movement in the linear track actuator would move the LED ligt rail 4 inches. While the actuator would only see 50 pounds of actual mass, it would require 200 pounds of force (1:4) to move the load.
As it turns out, Firgelli Automations sells a 10" linear track actuator that has a load capacity of 200 pounds and moves at 1" per second when fully loaded and 2.5" per second with no load. If this actuator is connected to the LED light rail via a 1:2 block and tackle pulley system, then for every inch it travels, the LED light rail will travel 2 inches. As mentioned, the entire force required to move the light LED light rail will be far less than 50 pounds and therefore, worse case, the linear track actuator will see a load of less than 100 pounds. The estimated speed of the actuator will be around 2" per second, translating to a LED light rail movment speed of 4" per second with a maximum travel of 20". Not too fast, not too slow, and the perfect tracel distance between the ceiling and top of the tank.
Linear Track Actuator
The foundation for the new hanging system is a linear track actuator that will be connected to a block and tackle system. At some point (for ease and repeatability) the actuator will be attached to a small microcontroller that can control and repeat height adjustments by the press of a button. However, for the sake of simplicity and quickly moving to a "finished" project, the intial control will be done from the wired 3 position momentary switch that sjipped with the linear actuator kit. Most affordable linear track actuators have simple maximum and minimum travel limit switches that are not adjustable. This will be taken into consideration when the linear actuator's total travel lenght is chosen.