The claw took me about a day to build, and cost me nothing to build. However, since it is relatively unlikely that you will have the required pneumatic parts ready, so it will probably cost you a bit more.
Step 1: Materials
- Pneumatic cylinder- make sure it has a large diameter, something over 2 inches is probably best. stroke length around 4 inches, and pressure handling of 110psi to be safe. check ebay. mine is a bimba stainless steel 2in diameter, 4 in stroke length.
- Plywood - i used 1/2 inch, 4ply for the gripper parts, and some thicker, 10ply? dense hardwood plywood i had laying around. the thicker stuff is mechanically indestructible. got the thinner stuff for a different project at lowes.
- 4 way poppet valve - i got mine for free, mine is a bosh rexroth type 840. check ebay. they are made specifically to extend and retract pneumatic cylinders.
-pneumatic tubing. size depends on your valve.
-pneumatic fittings: three hose barbs, depending on your tubing size. one coupling, one pneumatic quick connect.
-electrical switch and some wire.
- random (thick (3/8)) nuts, bolts and wood screws.
- 13.74g of common sense
Step 2: Designing the Frame
you can have frames with varying degrees of leverage, two moving claw pieces, linked mechanically or pneumatically. whatever design you choose, try to keep it simple, and prototype it in cardboard first.
Sketch your design on paper, from at least the top and the side view, that will give you a feeling for how you will stack your plywood to make it thicker. Keep in mind the dimensions of your cylinder, and its stroke length.
Unless you want to do a whole lot of math and trust your theory, i recommend making your design in cardboard first. this will give you a very good idea for the dimensions, tolerances, and any interferences between parts. use pencils for pivot points and to represent bolts. put your actual cylinder into your cardboard assembly, and try extending it and retracting it to see how your claw will function.
Once you have that, move on to the next part.
Step 3: The Woodwork
This Was the most tedious part of the whole assembly process...
1. trace onto the plywood around your cardboard templates you made earlier.
2. use a jigsaw to cut out the shapes. I cut out 3x part 1, 2x part 2, 2x part 3. the idea is that layering the plywood gives the thickness of the claw.
3. Sand or file to deburr the wood and get rid of all the irregularities between the individual pieces. (make the parts you stack the same, at least in crucial areas.
4. screw the parts to be layered together. For added strength laminate with wood glue.
Step 4: Assembly
This will be the most frustrating part of the build. you will have to repeatedly screw in and unscrew bolts, and figure out that things don't fit and modify them.
In my case, i bolted the lower arm to the body, and then the upper arm to the cylinder, then that assembly onto the lower arm and body.
add washers and spacers where needed to make everything nice and paralell.
Step 5: Pneumatics
The pneumatics will require some experimentation.
make sure to use thread sealer tape. it will make your life easier and it's cheap.
1. screw together the quick connect/hose barb assembly as shown in pic 1
2. connect tubing to the valve. finding out what connects to what is the hardest part to find out. 4way valves usually have two connections the cylinder, one for each end, one pressure in, and one exhaust port.
3.connect your tubing to hose barbs you screw into the cylinder.
done. wasn't that easy?
Step 6: Finishing Touches and Electrical
We're almost done now... now for the easy part.
We need a 12v signal to activate the solenoid valve, so you could either use 8 aa or aaa batteries, or a power supply. i chose a power supply because i had made one for a different project that was perfect for this purpose.
just connect the Powersupply in series with the switch and the valve. polarity does not matter in this case.
i made a little mounting plate for the switch out of a block of wood, which doubles as a rear spacer, so that i can tighten down the nuts on the cylinder mount/pivot.
Now go hook your claw up to your air compressor. start with your regulator set to a very low pressure, something like 30 psi. stand back, and wear safety goggles and ear protection in case something goes wrong or explodes. if all goes well, contijnue increasing the pressure until you reach maximum operating pressure. if all goes well, take off your ear protection and listen closely for leaks.
hook up your power supply and press the button. your claw should come to life!
Never put your or anyone's fingers or other appendages into the claw.
Now go and have some fun scaring your friends and crushing all those annoying things you don't need anymore.
Step 7: Troubleshooting
My claw isn't moving!
-check your electrical system for shorts and continuity. check your solenoid continuity (resistance). check your switch's functionality.
-check your pneumatic valve connections, and if they are correct. experiment with these.
My claw moves really slowly!
-check your pneumatic system for kinks or other resistance or leaks
-if your tubing is Really small, consider using bigger tubing.
-check how much air your compressor can put out. some cannot put out enough to power the claw continuously.
-check how tight your pivot bolts are. if they are too tight, they will produce too much friction to let the claw function correctly.
My claw is really weak!
-check for leaks
-increase the air pressure
-increase the leverage of your claw. this would require a complete redesign of the wood components.
Questions? comments? complaints?