Every year our church, The River Church Community in San Jose CA does a big Maker Camp ( http://www.rivermakercamp.org -- if you're around San Jose sign up your kids!!). I wanted a huge interactive display when kids walked in. So we made "Mt. Make" into a massive 12 foot high, 40 foot long marble run.
It's fun to be at a church that allows a lot of creativity and celebrates both science & God. If you want to see the kind of cool artistic maker stuff we do, check out this live art performance!
First of all, here are all the supplies you'll need:
- 4x pieces of 3.5in x 1/8in x 8ft clear polycarbonate (DO NOT use acrylic)
- 2x pieces of 1in x 0.5in x 8ft polycarbonate (DO NOT use acrylic)
- Note that if you don't have access to acrylic, you can also do this with plywood, but then it's obviously not clear.
- 10x 3/8" acrylic cubes (Available here) + Sewing needle & thread
- Acrylic Cement ( Available here)
Acrylic Cement bottle applicator ( Available here)
250 RPM 12V motor, Available here on Amazon .
- Note that you could also use a 120RPM version if you want to go steeper or slower, available here .
- 10meter 3D printer timing belt + matching 20 teeth timing pulley wheel with lock screw, Available here on Amazon .
- 5mm to 6mm shaft coupler with set screws, Available here on Amazon .
- 100mm x 5mm shaft, Available here on Amazon.
- A bunch of tubes & tracks for your marble to run! Get creative!!
- You can get 1" ID x 1.25" OD flexible rubber tubing at your hardware store. Here's the stuff I used, but it's way better to get locally so you can get it cut to length.
- You can use all kinds of stuff -- like pipe insulation, PVC pipe, anything that a marble will roll in!
Step 1: Make the Conveyor Belt Track
The first step is to make the clear plastic unit that will hold the conveyor belt and the marble as it rises up along the belt. Our goal is to make a 1" wide by 14 ft long track that will carry a marble 10-12 feet high.
I used clear plastic, but you don't have to -- I think you could use wood or any other kind of material. We're basically just making a long skinny 3 sided box. It should be 1" wide, and it needs to be at least an inch or two high. I made mine 3" high to make it stiffer. In my original configuration, it went 12 feet high without any supports. So I made the base of the box 1/2" thick polycarbonate, and the sides 3" tall, 1/8" thick (thicker would have been better, but made it too expensive).
Important note: You need the base to be 6" shorter than the sides on both ends of the track! This will allow us to place the conveyor belt pullies on the ends.
I bought 8 ft long sections of the sides & base of the box. But I only wanted it to be 14" long. So I cut 2 feet off one set of sections. I put the joint on the sides in a different place than the joint on the base of the box. You don't want all three joints to align, otherwise it would be likely to crack at that point.
Working with acrylic cement is pretty tricky. It has a very low viscosity and uses surface tension to pull into the joints of the pieces. If it goes where it shouldn't, it makes a permanent mark. I suggest watching this video to learn the applicator tricks so you don't make a big mess of the glue:
Here's another video that is helpful to learn how to put together the conveyor belt holder.
Step 2: Add the Conveyor Belt
The conveyor belt I used is 10m long, 32 feet. My track is 14ft long, but the belt has to run on the top & bottom, so I needed a total of around 28ft of belt. The belt comes with timing pulleys with a set screw. The timing pullies accept a 5mm shaft. You'll only need two timing pullies and two shafts.
I drilled a hole in the plexiglass just a little bit bigger than the 5mm shaft. The shaft hole is 1" from the end of the base of the track, and 1/2" above the bottom of the track. You'll need to put shaft holes one both ends of the track.
Next you need to install the pullies. It's a pain to get them in there and get the shaft through, but if you mess with it you'll get it.
The next step is the hardest. You will need to install the conveyor belt. It's hard -- you'll need a few people helping you. Wrap it around the track and the pullies. Stretch it tight, and then cut it to length. Be careful here, if you mess up on the cutting you can't go back!
You will need the conveyor belt stretched tight, but not too tight. If it's too tight, then the pullies won't be able to turn. If it's not tight enough then the pullies won't grab on the belt teeth. So you have to play around to get it just right. I found that if there's a couple inches of play in the conveyor belt near the middle of the track then it's about the right tightness.
Next comes the connecting of the two ends of the conveyor belt. This is the hardest step. There's a proper way to do it that's hard and requires special jig pieces. So I did a lot of experimenting and found a method using a stapler.
If you use a full staple that runs parallel to the conveyor belt, it'll break when it goes around the pullies. So instead, you can use a staple going perpindicular to the belt. Make the two ends of the belt overlap by about 1/2". You then aim one side of the staple right in the center of the belt. The other side of the staple will be hanging out off of the belt. Then you take a pair of snippers or pliers and you snip off half of the staple, leaving part of a staple hanging off to the side of the belt. Then you take a pair of needle noise pliers and bend the remaining part of the staple around that it locks onto the other side of the belt. You do that several times until you get a strong connection. It works great!
Step 3: Add the Acrylic Cubes That Carry the Marbles
I just 3/8" acrylic cubes to carry the marble. They work great, even at the steep grade. The marble rarely rolls off.
At first I just hot glued the acrylic cubes to the conveyor belt. But after an hour or so of running, the cube would fall off.
A better method is drill a hole in the acrylic cube. Then you can run a thin sewing needle and 4 pieces of thread the hole. You can puncture the conveyor belt with the needle and tie a bunch of knots in the string such that the cubes are firmly attached to the belt. You will want to put a cube every few feet, with perhaps up to 10 cubes. If you put on too many cubes then it'll get too heavy for the motor.
Step 4: Attach the Motor
I used a 250 RPM 12V motor. You could use something else, but I found 250RPM is just about perfect. I used a 12V laboratory power supply. You could also use a 12V wall wart or even batteries (as long as they were heft batteries). The motor uses about 0.5Amps when running, but needs a couple amps to startup.
The shaft for the motor I purchased was 6mm, so I used a shafter converter to go from 6mm to 5mm. I mounted the motor on a wood piece and wired it up! Remember you can switch the wires if the motor turns out to run in the wrong direction.
Step 5: Make the Marble Run!!
You now should have a conveyor belt that will deliver your marble to a height of 10-12 feet. Now comes the fun part! Make a marble run out of whatever you can find!
At the top of the run you can do a few different things to catch the marble. At the huge marble run I built at our church, I had the marble fall off into a 12 long wooden trough. In my home marble run, I had the marble fall off into a funnel. I cut the bottom of the funnel off, and then just taped it to the flexible tubing that ran throughout my kitchen, and back down to the start of the run.
I used all kinds of stuff -- a 12 foot wooden trough that I built, tubes, an acrylic S-turn trough, pipe insulators. But the best stuff is RVPN vinyl flexible tubing, 1" ID and 1.25" OD. I found it listed online here , but you can find it at any hardware store. Note that there are some types of clear tubing that are less & more flexible. You definitely need the more flexible version. Less flexible versions will bind at corners and the marble will get stuck.
When I first designed my marble runs, I built them with large downhill sections followed by short uphill sections. It looks good to have swooping downhills followed by uphills. But I found that eventually, a marble would get stuck in the uphill section, and then it was a pain to get it free. So I learned that you should NEVER have an uphill section. Here's a good test -- you should be able to stop a marble anywhere in the run, and then set it free and it should be able to roll to the end. If you use that rule, you'll never have a stuck marble.
I used a variety of methods to hang the run. At my house, I attached it to a pull-down staircase and a light fixture. At church, I hung everything with invisible fishing wire and "Command" brand adhesive hooks from the ceiling. The fishing wire made it look awesome -- it looked as if the marble run were floating in mid-air. But I found that the fishing wire stretched out overnight, and so every morning I had to come in and make small adjustments so that the marbles wouldn't get stuck.
This was a super fun project! It's so fun to be creative, and it's mesmerizing to watch the marble running. Kids at our maker camp just sat and watched it go!