Projector Lift

Background

My solution was to build a motorized projector lift. I was inspired by designs at SVSLifts, and their prices. I nearly had a heart attack when one of their kind salespeople answered my questions about their pricing (it's in the mid-4-digit range). I decided to build my own.

The basic design uses two "scissor" arms that connect a stationary platform mounted at the ceiling with a mobile platform mounted at the bottom of the arms. The mobile platform is actually suspended by 3/16" vinyl coated cable from a motorized drum mounted on the top platform. By turning the motor on, the drum collects or pays out (depending on the direction of the motor) cable and raises or lowers the platform. The scissor arms guide and stabilize the platform.

Mechanical

Here's a basic cross-section of the lift in the closed position. The projector is actually mounted underneath a platform that is mounted to the bottom platform, thereby emulating a ceiling mount.

All the metal parts used are aluminum stock bought at Home Depot. I had the parts for the scissor arms professionally milled so they fit correctly. All the remaining metal parts I milled myself using a bandsaw, drill press, and various hand tools. All the wood parts are 3/4" birch plywood, milled by myself.

You can see some screenshots of the plans for the aluminum arms here and here.

Since the scissor arms move in relation to each other, it's important to allow them to move smoothly and silently; I have no desire to hear the screech of metal as the projector moves into position. To accomplish this I used a a series of nylon washers and spacers so that no two metal pieces are in direct contact with each other.

The first motor I used for the lift was an old garage door motor I reclaimed after installing a new one for my mother-in-law. I think it was about 1/3HP. It had a 7 tooth sprocket driven by a worm gear. I left the motor and worm drive mounted to the original housing and trimmed off all the electronics. I made the aluminum diagonal braces from flat stock. The whole thing was mounted on a movable platform for the purpose of tensioning the chain. While this whole arrangement worked well, I replaced the motor later.

While looking on eBay for motor parts for the screen part of this project, I came across a good deal for a different motor. The new motor had one major advantage; it took up less vertical space which would allow me to mount the lift closer to the ceiling. It also had a lot more power and was built much more ruggedly. Since it's a parallel shaft gear motor, It needs a brake, which it came with. I had to add a sprocket, but a quick stop at Graingers took care of that. Since the sprockets Graingers carries take a larger chain than the garage door opener, I also picked up a new chain and a matching sprocket for the cable drum. The motor is shown unmounted, but it mounts to a slip plate just like the old motor.

The cable drum is an assembly I designed and built from 1 1/2" PVC pipe, 1/4" threaded rod, and oak (i.e., wood) hubs. The drum contains 3 oak hubs which hold 2 threaded rods that run the length of the drum in parallel. These rods stiffen the PVC pipe while there is also shorter threaded rods passing through the additional holes in the oak hubs, threaded into the steel axle.

The drum rotates on a solid 1/2" steel rod (the axle) which passes through a homemade pillow block bearing attached to the platform on each end. A sprocket is also mounted to the axle rod using a set screw. On one end of the axle I've attached a rotary quadrature encoder with a custom plexiglass mount. The encoder feeds the custom electronics (see below) with the drum's rotational position. The picture shows the old sprocket and motor and doesn't show the sensor or its plexiglass mount.

The sensor shaft is only 1/4" and is attached to the axle with a steel shaft coupler, also from Graingers.

Since the axle is 1/2" and the sensor is 1/4", I had to mill the end of the axle down to size using a homemade jig and an angle grinder. The jig is made of scrap plywood and 2x4, my 1/2" Milwaukee drill, and some clamps. The assembled drum is mounted in the drill chuck and the drill is turned on using a piece of velcro around the trigger. I uses the angle grinder on the end of the spinning axle sticking out on the right.

Here's the finished work. I also used the grinder to make a flat on the axle so the shaft coupler would have something to hold against. It worked surprisingly well.

This is what the sensor and its plexiglass mount look like when mounted to the axle and platform.

Here's the lift mounted to my garage/workshop ceiling. It's in the "up" position. While hard to see, the projector will mount under the piece of plywood above the bottom platform (it's inside the arms). That piece of plywood acts as the "ceiling" as far as the projector is concerned.

Another picture in the up position.

Here's what the lift looks like in the down position. It can actually extend 8' down, but my garage ceiling isn't that high.

Another "down" picture.

This is a shot of a late add-on to correct a problem I was hoping wouldn't be one. The cable is supposed to wrap nicely on the drum as the lift is raised but it has a tendency to spread out and ends up winding off the ends of the drum before the lift is fully raised. This device tensions the cable and keeps it winding more tightly. The round bearings/guides are actually patio door wheels made of solid brass that I picked up at Home Depot.

This is the top platform and motor mount slip plate after disassembly and 3 coats of clear gloss polyurathane. The black stripes are pieces of anti-slip stair tape made by 3M. It's like sandpaper with adhesive. The motor mount is upside down for the picture, but will be turned over so the tape meets the tape on the platform. This ensures the mount doesn't actually slip after it's tightened down with bolts after the chain has been tensioned.

These are some of the aluminum parts after painting. I first cleaned each piece with Comet Aluminum cleaner, then primed, then painted with flat black enamal. The result is a very nice, durable finish.

Here's the part of the lift the projector actually mounts to (almost). This is the top view. The 3 bolts sticking up pass through t-nuts on the other side and are tipped with rubbery caps. They apply pressure to a 1/4" plexiglass panel that is attached to the projector and allow it to be turned, tilted, and locked in position. The fourth bolt holds the plexiglass to the wood with a spring to provide tension.

Here's the plexiglass panel still with it's paper on. When the paper is removed, it will be clear. The "U" shaped cutouts allow for the cable as it passes on its way to the eye-bolts on the lower platform (not pictured).

Electrical

The lift and projector will share a 20 amp circuit with the screen, and have a 500VA APC UPS to provide clean power for the projector.

Enclosure

Installation

This is the new motor mounted on the lift platform. You can also see the position sensor wire in the lower right. After final installation, the motor mount will need to be adjusted to tension the chain.

The top of the frame is mounted to the ceiling with 6 lag bolts. You can see the aluminum brackets that will hold the UPS. You can also see where the old ceiling fan was mounted. That box will be removed and the hole will be reused for the 2" flexible conduit that will house the video and signal cables. There will a wire chase that matches the enclosure between the hole and the front of the enclosure.

The side panels and bottom frame have been mounted.

The bottom trim frame and main lift platform have been mounted. The picture also shows the change in daylight since the previous picture. Ther top of the 10' scaffold is also visible.

This is another angle of the same setup of the previous picture.

All the main lift components have been installed and the bottom enclosure face has been mounted. The bottom platform is suspended by a rope, barely visible in this picture.

Here's a picture of the wiring inside the enclosure. It's hard to see in this light but the UPS is mounted at the top, the motor controller on the left, and the power outlet just to the right of that. There are bundles of wire tied wires running between the controller and the motor, and all the sensor wires are clamped down with nylon wire holders.

The lift has been wired and is able to move up and down. This is the fully closed position. I wired the electronics and power 3 times before I was happy with how it looked.

Here, all the enclosure sides are installed as well as the wire chase. Inside the chase, the video cable, serial cable, and power cable are routed between the enclosure and the existing hole in the ceiling. You can also see the new track lighting and ceiling fans.

Here's the projector mounted in its new home. You can plainly see the corner guide blocks on the platform which align the platform and guide it into the upper enclosure when the lift is closed.

Here's another picture taken in front of the projector. You can see the video cable of the left side. It's housed in 1/2" flexible tubing that is wire tied up the right hand side of the lift arms. Power is wire tired down the left side of the lift arms.

Here's the lift in the normal operating position. It can lower another foot for maintenence, if necessary, but I can easily reach the projector in this position when standing on a ladder.

This part of the Home Theater Project is done! The lift works exactly as I intended and is able to accuratly position the projector with a high degree of repeatability. It takes about 25 seconds to fully retract or extend the lift. It's a little more noisy than I would prefer, but it doesn't operate while watching movies, of course. All in all, I'm very happy.