Intro: Electric Height Adjustable Desk
I wanted a height adjustable desk so I could stand while using my computer (but also sit when I wanted to), but I didn't want to spend a fortune on it and was also in need of a good project. So here's what I came up with. It's an electric desk that moves up and down at the flick of a switch. The height difference between sitting and standing is 18" and it takes about 20s from top to bottom position. All electronics are contained inside the desk, with only an AC plug coming out the back. The frosted glass, which was taken from a desk I had previously, worked out really nicely with the pine for a cool, modern look.
- Premium Pine (from Home Depot, about $150)
- Desk top (mine taken from a glass computer desk from staples)
- 2 x Linear Actuators (http://www.progressiveautomations.com/actuator-lin... $135 ea)
- 12V power supply (Amazon, $25)
- Voltage Regulator (Amazon. $15) - I'll explain this later
- 2 x DPST relays, 1 DPDT switch (Radioshack, $10)
- Various Hardware (~$30)
Thanks a lot to this guy for his inspiration! ->jwilcott's desk. I took some of his ideas and expanded on it.
Step 1: Design
This might be the most time consuming part of the process, but it should make everything easier in the end. I tried using SketchUp to design this, but learning that was a lot trickier than I had hoped... To the paper!
Sketch what you want it to look like. The actuator I chose presented a bunch of interesting design problems. I would actually recommend using something a little smaller, so you don't need quite so large legs and a big hole in the side of your desk for the motor (even though it looks kinda cool). The 200 lb rated load each might be a little overkill for a desk.
- I initially designed the outer and inner leg pieces to have a small tolerance between them (to facilitate sliding). Turns out you don't need that. If you have nice and straight wood, you can design without tolerances and then just sand down the parts if you need to. Of course make sure to make accomodations and tolerances for moving parts though. You don't want anything inside getting jammed or interfering.
- Make sure to consider screw placement. As I found out, screw placement can be a little annoying later if you haven't thought about it at the start. Screws start interfering with each other.
- When designing, try to use common plank sizes if possible (1x3's, 1x4's, 1x6's, etc). That will reduce your cutting time.
Step 2: Gather Your Materials
This was actually done of the course of several weekends (took about 4 weekends total). But here's a photo to make it look like I had everything together before I started.
Step 3: Cut and Assemble the Legs
I made each leg independently because the leg inserts and outer stands would be inevitably slightly off. It was important that each insert matched its outer stand perfectly. How the build process worked for each leg was:
1. Cut and assemble the leg insert (inner moving part). Clamps will be your friend.
2. Put actuator inside the leg insert and attached it, making sure that the actuator is spaced in the center of the leg (using bolts, nylon spacers, and washers).
3. Cut and assemble the leg stand (outer stationary part). My design required that I cut a 2-1/2" hole for the motor. Assemble this around the leg insert, making sure the two pieces aren't too tight and things can slide. Sanding may be necessary.
This is the process I used, but I ultimately ended up taking things apart a few times in order to put in the center support brace.
Step 4: Attach Table Top Supports and Try It Out
The desk top I used, which was taken from a glass desk I bought from staples, had four aluminum pegs attached to the bottom. This worked out great because I just drilled four 1" holes with a hole saw and the pegs fit nicely into the supports.
This is where it became apparent that the two actuators had different speeds. One was faster than the other... That's a problem because it means the desk will be on a slant while it's moving. There are several different ways I could address this, but I decided to take the easy route and put a voltage regulator on the fast motor, to limit its speed to that of the slower motor. I'll discuss this later.
Step 5: Build and Assemble the Center Support/Electronics Box
I wanted the center support brace to house all the electronics and controls, so I mounted the switch, power supply, and voltage regulator inside. The relays and wires are floating around in there as well. Lots of soldering required...
The speed matching works pretty well with this circuit, but it's not perfect. It is a little uneven on the way down. Fortunately, the down motion doesn't matter as much as the lifting motion because I always bring it to the bottom when I'm lowering the desk. Lifting is perfect though. Some ideas for a future desk:
- position control with an ultrasound sensor/arduino
- multiple settable height positions (memory)
Step 6: Button It Up and Enjoy
Attach the feet and button up the center support/electronics box and you're good to go. Enjoy your transformer desk!
Let me know if you have any questions or other ideas. I'd love to hear any ideas for making it simpler/cheaper/better/cooler. I considered lots of different possibilities before designing this. Some thoughts I had were making it mechanical, pneumatic, or hydraulic, but electric linear actuators seemed to be the simplest and best approach. Plus I'm not all that mechanically inclined.
Thanks again to jwilcott for inspiring the design.