Sunday, October 23, 2011

Pneumatic Toe Pincher Coffin, Part 2

On to the pneumatics. First I needed to find a quiet (and affordable) compressor to hide in the garage that won't make a racket. I settled on the GMC Syclone 6310.

I decided the best place for the pneumatic cylinder was at the foot so that it is not easily seen. The 72.5" long coffin will still have some room at the foot even after the 5'6" skeleton is placed inside.

I want the coffin to open automatically when someone approaches. I figured the easiest way to do this was to use a cheap Motion-Sensing Flood Security Light- without any light bulbs installed. Instead, a light socket outlet would be screwed into one of the sockets and an ungrounded extension cord run to the coffin. To keep things simple, as many of the components in the coffin should use 120VAC directly.

Working from the size of the bottom panel, 11-3/4" x 11", I had to find a pneumatic cylinder that would fit in the foot of the coffin. McMaster-Carr has the best selection of pneumatic components. I purchased the following items:

QtyMC Part #DescriptionEach
16534K18Quick Disconnect Hose Coupling 1/8" NPT female x 1/4" Industrial Plug$1.84
15644K91Assemble-Your-Own Retracting Air Hose, Red, 1/8" NPT, 25'$12.68
65644K51Easy To Install 1/8" NPT Male brass fittings$4.11
14414K32Air Filter$7.38
16692K16In Flow Control Valve, 1/8" NPTF to 1/8" NPTF$20.22
17889K22Directional Control 3-Port SS Solenoid Valve, 1/8 NPT Female, 200 PSI, 120 VAC$113.86
16498K5371-1/16" bore cylinder, 5" stroke, 1/8" NPT$36.54
19066K12Exhaust Flow Control Valve, Male Thread to Push-to-Connect Tube, 1/8" NPT For 1/4" OD$23.27
18457T31Push-to-Connect Muffler Plastic, 1/4" Stem OD, 52 SCFM$7.38
16498K72Pivot-mount cylinder bracket set$3.05
16498K43Rod clevis with pin$3.88

I could not find any 1/8" NPT rubber flexible air hose and ended up ordering some rigid retracting air hose. McMaster-Carr sells this along with brass fittings as part of their "Build Your Own Air Hose" solution. I cut the rigid hose into shorter lengths and attached the fittings to make three separate hoses.

To make sure everything works correctly, I "breadboarded" the components on the workbench to test them out.
I recommend using pipe joint compound on the threaded connectors before screwing them into the components to prevent air leaks. A squirt bottle filled with soapy water can be used after the system is pressurized to locate leaks.

The 1/8" NPT to "Industrial" Quick-Disconnect adapter allowed me to use standard air hose QD connectors - treating the system like any other air powered tool for use with the compressor. Home Depot did not have any black air hose so I found one made by Goodyearhere in the U.S.A.

One end of the 50' black air hose connects to the compressor. I set the regulator to 90 PSI. The other end of the hose connects to the quick-disconnect connector which goes to the air filter. The air filter removes any dust or debris from the air supply so it does not get into the components. The filter connects to an inline flow control which allows you to adjust the rate at which the coffin door opens. The flow control connects to the normally closed port on the valve. The cylinder connects to the port that is switched between the normally closed and the normally open ports. A 90-degree flow control is screwed into the normally open port on the valve. This flow control allows you to adjust the rate at which the coffin door closes. An exhaust muffler is plugged into the flow control to keep the noise of escaping air to a minimum.

Since the stroke of the cylinder is 5", the rod end will need to be attached approximately 3.5" up the lid from the edge.

An X10 RC6500 Key Chain Remote Starter Kitallows manual override of the coffin while the motion sensor light is tripped. This particular unit retains its on/off state even when unplugged. Leaving the unit "on" lets the motion sensor control the coffin. Since the motion sensor may be tripped prematurely, or may stay on too long, the remote control provides a means to manually close and open the coffin if multiple groups of kids are walking past the motion sensor.

Continue to: Pneumatic Toe Pincher Coffin, Part 3

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