Build a Pneumatically Actuated Yeti in a Cage for a Halloween Haunted House




About: Eric J. Wilhelm is the founder of Instructables. He has a Ph.D. from MIT in Mechanical Engineering. Eric believes in making technology accessible through understanding, and strives to inspire others to lear...
This pneumatically actuated, caged Yeti was part of the 2005 Occidental Haunted House that was the brainchild of Dale Dougherty, editor of Make. A giant pneumatic cylinder makes the monkey puppet appear as though it's trying to break out of the cage. Hidden air lines give onlookers a burst of compressed air in the face as they try to peer into the cage.

Step 1: Build the Cage

I used wood held together with biscuits and glue. I could have used screws, but I sure do love using my biscuit joiner. My cage is 24 in. wide, 27 in. tall, and 35 in. deep.

Step 2: Make Bars

After drilling holes through the wood, I dropped in scrap dowels and rebar to make bars.

Step 3: Make Ceiling and Floor

Cut pieces of plywood to make a ceiling and floor for the cage.

Step 4: Paint the Cage Black

I spray painted the cage black.

Step 5: Install Pneumatic Cylinder and Switch

The pictures are bit out of order because I installed the pneumatics first to test the whole thing out and then removed them to paint.

The 6 inch throw, 3 inch diameter double-acting pneumatic cylinder was a backup from another project that acutally needed such a thing. The valve is a 4-way, 2-position lever-operated control valve (part #4493k34 from McMaster-Carr). Both items are kind of pricey, so since being purchased originally for a consulting project they have been reused in a number of other projects. Compressed air is generated by a portable compressor used to power the air flow on the Squid Labs laser cutter when we take it to conferences or events.

The 4-way, 2-position valve is pretty neat. When you switch the position, it vents one side of the cylinder and pressurizes the other.

Step 6: Install Puppet Mount

I put a 2x4 on a hinge and tied it with innertubes to the piston. The 2x4 went into the puppet like a hand.

Step 7: Hidden Air Lines

Just under the puppet, I drill two holes and fed airlines through the 2x4. I connected these airlines to vent port on the valve. In this configuration, there would be a burst of air as the cylinder extended or retracted. Since the airlines were on the 2x4, as it and puppet moved, the airlines would sweep out an arc and be sure to blow on people of all heights looking into the cage.

Step 8: Wire Up the Monkey

I used some thick but malable wire to hold the puppet's arms out.

Step 9: Cover With Black Cloth

Cover the cylinder, 2x4, and hinge with black cloth. I used another one of my favorite tools, an electric staple gun, to help out on this step.

Step 10: Turn the Lights Down, Scare Some Kids

Red LED eyes would be a good addition, but I ran out of time.

I know this is terrible, but I feel that my Halloween creations are only successful if a few of the kids come out crying. Two Jacob's Ladders, low lighting, this caged Yeti, and everything else in the Haunted House seemed to do just the trick.

Happy Halloween!



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    14 Discussions


    11 years ago on Introduction

    god thats funny. nice instructable, i love it great awesome funny except it was a monkey not a yeti. ;)


    11 years ago on Introduction

    I actually saw it working cause i live really close to occidental. It was pretty awesome. Was a bit noisy though


    11 years ago on Introduction

    Neat instructable, What would be really scary is if you put leds in the eyes and made it so it would roar really loud.


    12 years ago

    You can also give the puppet an internal skeleton (armature) to hold his arms out. what pressure are you running, ~20psi? with that cylinder diameter you could really make that monkey leap out. also, ebay is a great source for cheap pneumatics, I got a 10 circuit, individually regulated, double action solenoid actuated manifold for $50.00. way bigger than i'll ever need, but it's great for this kind of stuff.

    3 replies

    Reply 12 years ago

    I can't quite remember the pressure, but it was probably around 30 psi. The monkey did move pretty quick, but I was mostly concerned about compressed air at too high a pressure spraying out the front from the hidden airlnes. I aimed for startling, but not dangerous.


    Reply 12 years ago

    hehe :-P

    If I can dig up some pistons, I will definitely try to do this. But I don't know if I have them...
    (I know I have a compressor, so I should have pistons, right?)


    11 years ago

    you could even cover it completely up with cloth and replace the 'yeti' with something less expensive so the cage just jolts around a bit


    12 years ago

    Awesome! I skimmed the instructable, so maybe you can't do this, but I would replace the wire with fishing line, so you can't see it.

    1 reply

    Reply 12 years ago

    In low light you couldn't see the wire, so it wasn't a problem.