Build Mini Conveyor Belt As Slinky Machine

This little project uses a yellow geared motor to power a 1 foot long conveyor belt made from pvc pipe, 1 by 4 pine wood, and artist canvas (for the belt). I went through a couple of versions before it began to work, making simple and obvious mistakes. The yellow motor, at 48:1 geared motor, probably about 140 size, has about 1 kilogram of torque which is just enough to get this working. But, the slinky will not "walk" indefinitely on the belt - my longest run has been 91 (207 latest) slinks or steps. Still, great fun to build and play with and to try to figure out how to make it better. The video shows the machine reverse engineered and I have included some pictures here for clarification and some problem resolutions.

Update May 8: just did 207 slinks or steps. To do this I decided to sew the belt rather than use staples and so it doesn't catch on the conveyor belt bed now and does a pretty consistent rotation on the rollers. I did notice too that while watching the slinky machine, the motor would change speed a little so next step is to try PWM motor controller to see if I can get consistent motor speed. Amazing the little yellow geared motor works so well!

You need two rollers, one to which the motor is attached and one at the other end of the frame so that the belt can loop around. I made mine from 32mm diameter pvc pipe. My rollers are 8cm wide, for a belt 6.5 cm wide which is the same width of my slinky, 6.5 cms. In hindsight, I should have made the belt a little wider but it does work at this width.

Into the ends of one of the pvc sections I epoxied a plywood circle. Then drilled a hole into each one and ran a 3mm threaded shaft through the center and secured it with two lock nuts. This roller is the idler roller that will be mounted at the bottom of the frame.

The second roller is the power roller and has to be built a little differently as it is attached directly to the geared motor. In one end I epoxied a plywood circle and drilled a center hole. Into the other I epoxied the plywood circle about 2cm down into the tube. I then cut out the center section of a wheel that mounts on the geared motor and epoxied it to the plywood circle. This now allows the roller to be attached directly to the geared motor just like a wheel would.

Motor mount: I used a 2cm by 2cm piece of angle aluminum to mount the motor by drilling one hole so that the motor can be secured to the aluminum by one bolt. Then I drilled a couple of mounting holes in the aluminum and mounted it to the wooden frame.

The next step will show how to construct the roller shaft bearing holders.

The roller shaft bearings are just a short piece of plywood that hold 1cm outside bearings with a 3mm center hole for the 3cm shaft. I glued the bearings into the wood with superglue. Then I mount the holder to the frame with a wood screw through a metal washer. These need to be allowed to rotate some to control the tracking of the belt.

The belt is probably the most problematic thing in a conveyor belt. I have seen some made from rubber inner tube, felt cloth and rubber sheets. I saw another project using canvas material and I am an artist so I just cut a straight 6.5 cm wide piece out of one of my unfinished paintings and it works quite well.

To mount it on the wheels I just stapled it using to staples from a stapler. It does not seem to adversely affect the operation of the belt when the motor is pulling it but it probably should be sewn to prevent the staples from slowing the belt when it goes around the rollers. (UPDATE: stapling does affect the operation of the belt - it leaves little seams that hang on the belt frame. I sewed the seams together and it works much, much better.)

Now one of the things I learned is that you need to add some material of some kind to the power roller at least to grab the belt as without it the belt will slip and the slinky will quit walking. I used electrical tape. Build up a little mound of it near the center of the roller as this will help keep the belt in place. Also I put some on the idler roller but probably not really necessary. Ideally some tight fitting inner tube as the friction material would be ideal to keep belt slippage to a minimum and I will probably do this on my next version.

The frame is just a couple of odd shaped pieces of plywood mounted on a two piece (it could just be a single piece) of 1 x 4 pine. This would be a great application for a 3D printer. The frame will hold the conveyor belt at the proper angle which is approximately 20 degrees from horizontal. It can be adjusted by adjusting the frame screws or just putting a small piece of wood under the front or fear of the frame to change the angle.

The conveyor belt needs some side rails to keep the Slinky from falling off the side of the belt and it needs a back plate or back rail to keep the Slinky from falling of the top end. I believe the back plate also serves to help flip the Slinky over. The back plate is just kind of hotglued in there until I can make a more permanent fixture. You have to experiment with the angle a bit until it is working right. There is no need for a front plate or rail as the Slinky should not get far enough down the belt to encounter it. And if the Slinky does get that far then there is a problem and the belt should be speeded up or the angle of the frame decreased slightly to slow the Slinky's walking pace down a bit.

I have an adjustable power supply with a potentiometer built into it. It is rated at from 6 to 12 volts and I measured the working voltage at 7.3 volts that would get the Slinky walking. It will be different for everyone no doubt.

If you do not have this adjustable power supply available then cheap PWM dc motor controllers are available that take from 6 to 36 volts input and output whatever you want as they also have a potentiometer. But you must have some way to control the voltage which controls the speed of the motor.

On my machine, the angle of the frame is about 20 degrees from horizontal but you may have to play with that a bit. The range of degrees with this little motor is going to be very small where it will operate correctly. You must adjust the motor speed to the angle.

This little motor is at the very bottom of the scale when it comes to useful torque for this project in being able to pull the weight of the Slinky and the friction of the belt. It really needs to have a much larger geared motor. I have a 550 sized motor that outputs 10kg of torque or about 10 times that of the yellow motor. At some point I plan to utilize that motor. But I wanted to see if it was possible to use the yellow geared motor successfully.

The longest number of slinks that I counted consecutively was 91 (207 now)so that is my record so far.

I don't know why I can't get longer runs but I suspect that #1, the motor is not pulling with a consistent RPM. #2 is that possibly over time, the belt stretches a bit and this causes it to slip. So perhaps a better belt material is called for.

A Kickstarter project, the Never Ending Slinky Machine (Project NESM) , failed to make it into production but it seems theirs works consistently. I am not sure if theirs stops working at some point or not. They don't show any really long runs. Not sure why they halted production. They definitely use a larger geared motor. But my contention is that if the Slinky never stops walking, where is the fun in that. It is kind of fun to see if the next walk of the slinky will be a new record. I think I would have wanted their project to be open source (they brag about how they kept their measurements secret like KFC) and made it solely a kit for others to put together. They actually charged more for the kit version.

TODO:

1. make idler roller using bearings to tighten the belt and prevent slippage. Done.

2. sew the belt ends together instead of using staples as they probably slow the belt down when they go around the rollers. Done - works much better - got new record of 207 slinks.

3. try big geared motor using pulleys and belt. Probably won't do this now as the yellow motor seems to be powerful enough to get some long runs (walks, slinks, whatevers).

4. Will try using PWM motor controller to smooth out motor rpm.

Anyway, this is a fun project that I am sure I will work on in the future, especially with a more powerful motor to see if I can get more consistently longer runs (but not perfect ones).