This slinky machine plays with a slinky for you.
This instructable presents a video of the machine operating and also some general guidelines for building your own machine.
My basic rule of construction has always been, just use what you got.

Not a lot of science here except an interesting observation: the slinky provides a feedback circuit to the motor and so you get an uneven cycle of operation - the machine goes at two speeds depending on where the slinky is in it's cycle. Kind of fun to watch.

If you want to see a couple of really fine examples of some other folks well crafted slinky machines, look here:

http://technabob.com/blog/2010/08/11/slink-o-matic/

http://bellsouthpwp2.net/w/r/wrobinson/proj/wood/wood.html

Step 1: Frame of the Machine

The frame is just a short pine board mounted 90 degrees to a base pine board. Held together with a single corner bracket.

Step 2: Drive Motor

The drive motor is the motor/gearbox and one wheel from a toy truck. Only the left motor and wheel of the assembly are being used here. I actually reused this from a previous instructable project.

The motor is battery powered but I use a little adjustable power supply so that I can play with the speed of the machine.

The gearbox is zip tied to another plastic block which is attached to the wood base with wood screws.

Step 3: Drive Shaft

The drive shaft is a piece of hollow fishing pole. I attached it to the drive wheel with a 6 inch metal strip. As the wheel turns it simply pushes and pulls the pole shaft up and down.

The second photo shows probably the most complex part of the machine. It is simply a paper clamp which has a hole drilled through it to mount it on the wood frame. The paper clamp holds a 3 inch section of fishing pole that the drive shaft pole fits inside of.
I used two nuts to make the paper clamp stand out from the wood a bit.
I also used a couple more screws/bolts to keep the paper clamp from turning when the shaft is moving.

Step 4: Slinky Holder on the Drive Shaft

The slinky holder is a plastic peanut butter lid. The lid is great for holding the slinky as it has a lip that keeps the slinky in place.

Use magnets on the bottom of the lid to hold the slinky in place.

The lid is attached to the drive pole or shaft with a couple of bent metal strips. Use whatever is available to attach the shaft to the lid.

Step 5: Slinky Holder on the Other Side

The first picture shows another corner bracket attached to the wood with a wood screw. To this I attached another lid I found in my kitchen. I hotglued some magnets to the bottom of the lid to hold the slinky.

The last photo shows the backside of the machine.

And thats it. Plug in your batteries, put the slinky on the machine and enjoy!