Coffin Lid Slider Halloween Prop

This is a project for Halloween that has gotten very good comments from the trick or treat visitors.
It consists of a wooden coffin with a lid that slowly slides to the side while lifting a skeleton up a few inches.  Smoke pours out and a creepy laugh sounds out.  Then after a few seconds the lid slides back and the skeleton lowers back, resetting for the next trigger.  Below is a video of how this is supposed to work.  http://youtu.be/ha0Bh_MUB3M

And here is the full yard showing the coffin in action.

http://youtu.be/0TV9UUx-iSs  The coffin is at about 5:20 time code.

NEW!!!!!
I have added some modifications to the design.  The lid turned out to be a little fragile and I didn't like the way the Skeleton was attached to the coffin.  So see the added steps at the bottom.

Step 1: Material List

Supplies needed.
1. 2-½ inch 4 x 8 plywood sheet
2. 2 1½ x 1 ½ stock
3. Gear motor (I got mine from Granger a while ago when they offered the 6rpm’s at a good price)
4. Fog machine (small one)
5. Aluminum or steal flat stock
6. Two limit switches
7. Fishing wire
8. Light weight skeleton
9. Prop1 Controller board from EFX-TEK
10. RC-4 with 3 Solid state Relays from EFX-TEK
11. Cowlacious CAP200 and sound chip
12. Speakers
13. Power strip
14. Plastic milk jug
15. Screws and ¼-20 bolts
16. 3/8 steel rod.  Only need about 2 inches.

Step 2:

First you need to construct the box.  I glued and screwed the box together without a top, using the dimensions shown below.

Step 3:

Then I took the 1 ½ x 1 ½ and cut dadoes in the edges on two sides. The dado is ½ by ¾.  I also cut one edge at 45 degrees. This is what you should end up with as a cross section.

Step 4:

Now you need to cut and miter four pieces to size to fit around the inside of the top opening.  Then screw these pieces in place.  DO NOT Glue.  This will be part of your removable top.

Step 5:

Then cut a piece of plywood to fit into the dado on top.  Glue this into place.  When dry keep everything together and fire up your table saw.  WITH HELP I used my table saw to cut up 9 ½ inches to create a 3 ½ inch top.  Please don’t try this without a second or third helper.  I accept no responsibility if you don’t head this suggestion. 
You should now have something that looks like this.

Step 6:

I painted mine to resemble stone using the Stone texture paint you get at Home Depot.  It comes in a few different colors but I like the gray color the best. 
Now after it has dried you need to add the reinforcements and the block for the swivel pin.
All braces and blocks are the 1 ½ x 1 ½ stock.

Step 7:

For the motor and assemble you need to play around with the geometry.  Below is loosely what I did.  Each bolt has a large fender washer in between the Aluminum arms to provide a sliding surfaced.  Tighten the bolt and lock nut to a point where you just have a little friction.  You may want to put a little grease on the pivot point.

Step 8:

This is what you should end up with.

Step 9:

Finally you need to connect the electronics.  I used the Prop 1, RC-4 from EFX-TEK.  You can get the code here
http://www.efx-tek.com/php/smf/index.php?topic=1231.0
The sound is board is from Cowlacious Designs and you can see it all hooked up here.

Step 10:

For the raising and lowering of the Skeleton I just used a bit of fishing line attached to the head, coffin side and lid.  The movement of the lid would raise and lower it.

Step 11:

Here is the bottom fog machine and speaker area.  I replaced the original fog reservoir with a gallon milk carton.  I fill it to the top and you can see the fluid level in the picture.  Turns out that it only used less than a half gallon of fluid.  Speakers were glued to the bottom of the coffin side

Step 12:

This is the inside with the top off.  I am able to get to everything inside and make any adjustments.  The skeleton was from the skeleton store.  This was the lighter plastic version for $49.

Step 13:

Here are some more view showing the PIR sensor, details of the top and how it is attached. 

Step 14:

And here are some view showing the piviot pin.

Step 15:

So after a few seasons of opening and closing I found that the lid was starting to come apart a little.  So I decided  to update the lid and strengthen it.  I also was not completely happy with the way the skeleton tracked as it raised up.  I purchased from Home Depot some 2" x 2" x 8' fir stringers.  I then cut these to fit around the inside of the lid.  Mitering the corners.  I then glued them in with Gorilla Glue making sure to get them flush with the bottom of the lid.  I also screwed them in to the sides every 10" to make sure the sides strait and secure.  I also strengthen the joints with "L" and "T" brackets.

You can also see in one of the pictures the motor arm is now attached to the 2" x 2" and not the sides.

For the skeleton I cut a 1" X 1" aluminum angle into two pieces.  The longer one is attached to the back side of the skeleton along the spine and the shorter one (about 4") is attached to the bottom of the coffin.  I then drilled a 1/4" hole into the ends of the two aluminum angles and inserted a bolt to act as the pivot point. 

Finally I added a small spring attaching it to the free end of the aluminum angle and the bottom of the coffin.  This spring keeps the Skeleton moving in a straighter fashion.

I then changed the fishing line to having multiple loops attached to two screws acting as a spring for the main fishing line that lifts the head.

Step 16:

Here are the videos of the modifications with the top removed so you can see the workings.  And even after the modifications it still has the sliding, scraping, groaning sound of the lid opening.