Hi! If you like this Instructable, please vote for me in the Halloween decoration contest! I really appreciate it!

Also, check out my other Halloween Instructables:

Scary animated hangman:https://www.instructables.com/id/Animated-Hangman-...

Ultimate Fog Chiller: https://www.instructables.com/id/The-Ultimate-DIY...

I Love Halloween! It is a big deal in our little town and people really go all out. We've been slowly adding to our yard display over the last few years. I try to add a little something new each year. My latest creation is a pneumatic zombie ground breaker. He's busting out of his grave to eat your brains and swallow your soul.

This was my first time working with pneumatics. I think they are a perfect fit for a zombie, as the movement is very fast and creates a wonderful jerky motion.

Our friend can push himself up from the right side, left side, or both sides at once. Using the controller, I recorded a sequence of movement and audio to be triggered by a motion sensor when a small child gets within range.

I bought the controller, pneumatic cylinders and solenoids from Fright Props and I highly recommend them. They have detailed instructions for all their products that make getting up to speed super easy.

Supplies

A stick of 2x4 wood
Some pvc pipe for the zombie neck
A foam mannequin head(https://www.amazon.com/gp/product/B00KCSZOVU)
A scary mask and some old clothes (I got an old shirt, tie, and jacket from goodwill)
6 hinges
miscellaneous bolts and screws
2 cylinders startup kits(solenoids)(https://www.frightprops.com/cylinder-hook-up-starter-kit-double-acting.html)
2 pneumatic cylinders with mounting hardware(https://www.frightprops.com/1-1-16-inch-bore-double-acting-universal-mount-cylinder.html)
1 manifold for distributing the compressed air(https://www.frightprops.com/aluminum-block-manifold-with-fittings-for-1-4-airline-4-ports.html)
1 controller to run the show(I used the PicabooPlus: https://www.frightprops.com/picoboo-plus.html)
some pneumatic tubing and quick connect fittings
a speaker
a motion controller to trigger the zombie(https://www.frightprops.com/prop-controller-motion-trigger-black.html)

Additionally, you will need a source of compressed air.

Step 1: Build the "Bones" and Attach the Hinges and Cylinders

In the first picture you can see the five 2x4 pieces with the dimensions marked. The shoulder joints are cut at 30 degrees.

After you cut the pieces, you can go ahead and attach the hinges. Note that at the upper arm hinge there is only a single bolt used. This allows the joint to rotate as needed. Use two nuts tightened hard against each other on these so the shoulder can rotate freely, but the bolt won't come loose (see pic).

I used bolts for the shoulder hinge connections as well. There is a lot of force from the pistons at this area and you don't want your zombie to tear itself apart. For the "elbow" joint, I used the wood screws that came with the hinges.

Next, you can attach the two pneumatic cylinders. What I did was set the piston so that when fully extended, there is still a slight bend at the elbow. This looks more natural and will be the maximum extension possible.

For a base, I just used a piece of plywood I had lying around. The distance between hinges was about 27"(refer to pics).

At this point the basic frame is done! In the video you can see the three basic movements (left side up, right side up, both sides up).

Step 2: FAILURE 1: Experimenting With a Rotating Head

I thought it would be cool to have the zombie head rotate. I figured the easiest way would be to harness the motion from the pistons. You can see what I came up with in the pictures. Essentially, the pvc neck is supported by 2 skateboard bearings. This allows it to rotate freely, but keeps it from falling through the hole.

I then ran bungees from the pvc to the arms to create tension. This holds the neck looking forward when everything is at rest. When one shoulder is raised, it increases the bungee tension from the opposite side and reduces the tension from the raised shoulder side. This causes the neck to rotate.

Although it worked fine, after messing with this for a couple hours, I decided that the complexity outweighed the added risk of something breaking and I discarded it. It's something I might revisit if I were to do this again and had more time.

Step 3: FAILURE 2: the "Always Upright Head" Experiment

Next I decided try having the neck always being pulled vertical. This would keep the head upright even when the shoulder are tilted. To do this, I enlarged the hole in the wood the pvc neck goes through into a slot, running towards the shoulders(you can see this in the first picture). I put a bolt through the wood and pvc, creating a pivot point. I then attached a bungee to the bottom of the neck and anchored it on the plywood base. When the shoulder is raised on one side, the bungee keeps the pvc pipe vertical.

Or so I thought. Once I hooked up the pneumatics, there was just way too much bouncing for my liking. It looked too comical and not super scary at all. I discarded this idea at this point, but a way to get around this might be to have a narrower pvc or dowel connected to the base that slides inside the neck to keep it vertical.

Step 4: Putting It All Together and Scaring the Children

At this point, everything can be hooked up and we can dress up our friend.

I won't go into deep detail on wiring but I created a simple diagram and you can see from the photo how I mounted everything to the base. Basically, you have the air running from the compressor->manifold->solenoids->cylinders. The speaker, strobe light, motion sensor and solenoids are wired to the controller. Fright Props has some excellent and detailed instructions for all their products, which cover hooking everything up and programming a run sequence into the controller.

I mounted the foam head onto a piece of PVC, using some hot glue. I added a bit of mesh screen for the chest area to create some form for the shirt.

*NOTE* I recommend starting with a low amount of pressure when testing and increasing from there until you are satisfied with the speed. The cylinders are very powerful and you don't want to rip everything apart.

You will probably want to either weight or stake down the groundbreaker to keep it from shaking across your lawn. I ran a considerable length of air hose so I could keep the compressor in the back yard, since it is rather noisy.

I've attached two videos of the device "in the wild", one during the day, and one at night with the lights and fog going. In the second one you can also see the animated hangman in action.

Anyway, that's it! Please let me know if you have any questions. I tried to include a lot of pictures, but if there is something you want to see that is missing, let me know.