After using the pulley rig I designed here: http://www.thingiverse.com/thing:566 for a few weeks I realized that the rubber band was clinging & slipping quite a bit. I tried a few different things as a pulley belt, but nothing worked to my satisfaction. So I redesigned it to use a set of gears instead, which totally eliminated the slippage and greatly improved the accuracy.

One thing to remember though is that while pulleys move wheels in the same direction, with gears the dimmer will turn in the opposite direction of the servo, so be sure to adjust any code you may have written accordingly.

What you need:

Material (Rough sizes, you could probably compact the parts some)
7" x 11" 16th inch acrylic x1
4" x 8" 8th inch acrylic x1



Fasteners
1/4" #0 machine screw x2
3/4 #6-32 bolts x5
3/8" #6-32 bolts x4

6-32 nuts x 4

1" #4-40 bolts x4

4-40 nuts x4

Other Hardware:
NEMA compliant Rotary Dimmer Switch x1
NEMA compliant Outlet x1
Power cord x1
3 gang junction box x1

Electronics
HS-322HD Servo x/ small wheel horn x1
(Oh, and an arduino and wall wart for good measure)



Inside the 3 gang box wire up your outlet and dimmer switch to your electric plug , match the colors, it's fairly simple.

Cut your pieces. Face plates from 1/16th inch acrylic, pulley bits from 1/8th.


Attach the servo to the underside of the top faceplate layer. Make it tight, but not so tight that you can't adjust its position.


Fasten the two faceplate layers to your junction box, the bottom layer has larger holes to give all the hardware's raised parts clearance. In the smaller holes use the 3/4" #6 bolts (NEMA standard)


Laminate the smaller gear making sure the half circles all line up. Fasten with 2 of the 3/8" #6 nuts and bolts.

Compared to the big pulley in the original version of this project, the big gear is easy to put together. Laminate the two layers together with the heads of the bots on the bottom side (to ensure clearance of the servo horn) and then fasten the whole rig to the servo horn.

Put the small gear on the dimmer and the large gear on the servo. Adjust the servo side to side as necessary. Remove the large gear and fasten the servo down the rest of the way. Adjust both the dimmer and the servo to 50% (90 degrees on the servo ~a half rotation on the dimmer) and reattach the large gear and fasten down the servo horn.

And voile! You have a geared dimmer box, perfect for automated dimmer control, complete with a really satisfying sound.


For the code to run it on, check out the Arduino playground's servo tutorials. The HS-322HD has a full 180 range and the 2:1 ratio of the gears enables that to fully rotate the dimmer switch.