Introduction: Slinky Machine
I've wanted to build an automatic slinky machine for years, but the custom width/length belt left me stumped--until now. You can make your own custom belt using cardboard and tape; it really works!
Supplies
Cardboard
1" wide Gorilla tape (any sticky, strong duct tape)
Glue
30" Velcro
Misc. 3mm screws
1/2" plywood--12" x 15"
Servo motor (without end stops)
Slinky
3d printed parts
(8) 1/2" wood screws
DC power supply variable (5 volt to 10 volt, 1/2 amp)
Step 1:
Let's start with the belt. Cut (22) 4" x 1" pieces of cardboard. Place them in a straight line, space between each piece, so that the total equals 30".
Step 2:
Add tape on one side, then the other. Create a "belt" by taping the inside together, then the outside. I used about 6" of tape to overlap the joined spot.
Step 3:
Print the 3d pieces. The cylinders take about 8 hours each, so this portion is not fast.
Attachments
Step 4:
For a metal gear drive motor, easy to attach via servo horn, I modified a "no stop" servo motor.
Start by removing the four screws in the bottom of the case.
Step 5:
Next, cut the two wires from the circuit board that go to the motor.
Step 6:
Cut the three wires from the circuit board to the potentiometer. Remove the circuit board.
Step 7:
Take the two wires from the motor and solder extender leads.
Step 8:
Push the solder connection joints into the cavity of the servo motor housing.
Step 9:
Screw the bottom cover back into place. Set this aside for the moment.
Step 10:
On one of the pulleys, apply tape to match the tape position on the belt you made earlier. This provides a bit more friction for the drive pulley (the 3d printed pulley is somewhat slippery).
Step 11:
Secure an axle to one end of the driven (no tape) pulley.
Step 12:
Add the other axle using 3mm screws.
Step 13:
Press snowmobile bearings in the bearing holders.
Step 14:
Press a bearing in the tall bearing holder.
Step 15:
Secure the motor to the motor bracket using 3mm screws.
Step 16:
Attach an axle to the drive pulley.
Step 17:
Secure the servo horn to the motor axle using 3mm screws.
Step 18:
Attach the servo motor to the motor axle using the servo screw (there is a hole in the axle so that a screwdriver will fit).
Step 19:
Attach the motor axle to the drive pulley using 3mm screws.
Step 20:
Paint the plywood (if desired) and attach the bearing and motor holders using wood screws. Be certain that the belt is reasonably tight (depress less than 1/2 " midway between pulleys).
Step 21:
Add velcro to the belt--it's just a bit too slippery for the slinky without the help.
Step 22:
Make two side supports. The lower piece of cardboard is about 2 1/2" x 3 1/2". The upright piece is 3 1/2" x 7". Glue together at a 90 degree angle--I used 1" x 2" wood scraps to firm up the angle.
Step 23:
Glue 4" x 13" cardboard (at an angle) to the upright cardboard supports. These side walls must not touch anything that moves.
Step 24:
In an ideal world, the pulley will rise 13 units for 33 units of horizontal length. I didn't get this correct, so my 1" Gorilla tape under the foot of the system makes this work.
Step 25:
I turn the motor on (about 8 volts in my example--around 200 mA) and set the slinky on the bottom of the belt. As the slinky moves toward the top, I lift the upper part of the slinky and pull it downward. Two or three tries and you'll get the hang of it.
Usually it will run a minute or so until it runs off the bottom or top (feedback and stable acrylic walls might enhance the run time).
Enjoy :)

Participated in the
Recycled Speed Challenge
12 Comments
2 years ago
I could watch this all day!
Question 2 years ago on Step 10
When you printed your pulleys did you use any supports?
Answer 2 years ago
Yes, I printed them standing upright (like a can) at 10% fill (PLA) using supports. I'm using a MakerBot Replicator 2--each pulley took about 8 hours.
Reply 2 years ago
Cool ta, mine are coming up as 9hrs due to the speed of my 1st layer, I have an ender 3 pro, so I've had to separate the big sides cutting the foot off to get them to fit as they are just too long!
Reply 2 years ago
You might enjoy looking at this old Kickstarter project, the "Never Ending Slinky Machine." https://www.kickstarter.com/projects/creatableslabs/project-nesm-never-ending-slinky-machine
It was fully funded, but never produced . . . that was my inspiration to try this.
Reply 2 years ago
Best of luck on your print job--I always get nervous when anything takes more than 3 or 4 hours. This is a sturdy mechanism, just takes a lot of time to print the pieces :)
2 years ago
If you have an ultrasonic distance sensor or a magnetic metal detector coil- you could set that up to run the motor faster when the slinky gets too far back and slower when it gets too far ahead, and make it run endlessly.
2 years ago
Great!
Maybe you can finally answer that question that has haunted us all!
What is the lifespan of a Slinky?
Reply 2 years ago
For some... less that 10 minutes. LOL
2 years ago on Step 25
That is hypnotizing. How long have let this run? I'm assuming you've seen Matthais Wandel's version of this (https://youtu.be/5UP_njBPpZ4). I think your's works better. Excellent work.
Reply 2 years ago
Three minutes is about the longest run I've seen so far . . . it was put together in a hurry using cardboard. I'm thinking it might run indefinitely if a few issues can be ironed out :)
2 years ago
That's genius!!