Motorized Marble Run

This project will allow you to create a fun motorized marble run with easy-to-find materials! Learn a little bit about gear ratios, magnetism, gravity, and electricity while also enjoying the exciting process of making something new!

Materials:

• 5.5" x 6" plywood square
• 4 small furniture pads
• 16.25" x 1/8" diameter (Ø) metal rod
• 3000 rpm DC motor with small gear attachment
• 4 plastic gears
• 1 medium size (Ø1", 40 teeth) with small attachment (Ø0.33", 8 teeth)
• 2 large size (Ø2", 64 teeth) with medium attachment (Ø0.67", 20 teeth)
• 1 large size (Ø2", 64 teeth)
• 1" bar magnet
• 15 large paper clips
• 3" x 3" cardboard square
• 2 x AA battery case
• 2 AA batteries
• Simple switch (SPST)
• 3" or 4" of wire
• Metal marble (Ø0.5")

NOTE: These are the materials that I used because they were easily at my disposal. If you have trouble finding one or more of these materials in a certain size or dimension, don't worry. You can easily substitute other sized objects in for most of these materials. However, keep in mind that a substitution will likely influence other materials that you will need as well. Before purchasing any materials, I would recommend reading through this entire Instructable so that you have a broad overview of the project and understand how one material substitution may affect other materials.

Tools:

• Drill
• Hot glue gun
• Soldering iron
• Superglue (optional)
• Pliers

First, cut out a 5.5" x 6" piece of plywood if you have not already. Then, drill three 5/32" holes through the plywood at the locations designated above.

Flip the piece of plywood over and add a small furniture pad to each of the four corners. Flip the plywood back over and set it aside for a moment.

Now cut off two segments of lengths 3.75" and 2.75" from the 1/8" diameter metal rod. Take the plywood and place it in the orientation shown in the picture above on the left. Put the 3.75" rod in the left hole and the 2.75" rod in the right hole. Hot glue them in place. Leave the center hole empty for now. When finished with this step, your project should look like the picture above on the right.

If you are using modified materials, read the next two paragraphs before moving on:

Using a motor with a different speed will cause you to have to choose different sized gears (or include more or less gears) in order to produce a gear ratio capable of slowing the final output gear to around 5-10 rpm. Use the gear ratio formulae above to calculate the necessary number of teeth in each gear of your gear train. Also note that individual gear ratios can be multiplied if they are set up in a compound gear train. For example, in my gear train, I had a 3000 rpm motor rotating an 8-tooth gear which meshed with the next 40-tooth gear. This 40-tooth gear was connected to an 8-tooth gear which meshed with a 64-tooth gear. This 64-tooth gear was connected to a 20-tooth gear which meshed with another 64-tooth gear. This 64-tooth gear was connected to a 20-tooth gear which meshed with a final 64-tooth gear. The following calculations show how 3000 rpm was reduced to 5-10 rpm with this compound gear train:

3000 rpm × 8/40 × 8/64 × 20/64 × 20/64 = 7.32 rpm

Experiment with different gear ratio combinations based on your available supply and then move on to the rest of this step when you are ready. Also keep in mind that changing the number or size of gears will affect the size and structure of the gear train scaffolding.

Begin by assembling the four gears and cutting the remaining metal rod into 0.65", 0.75", 0.85", 1", 1.25", 2.5", and 2.75" pieces. Assemble the metal rod pieces into a gear train scaffold as shown above. Connect the pieces using a soldering iron and some solder, a hot glue gun, super glue, or other adhesive method. Which method works best will depend on what specific material or type of metal you are working with. When I built mine, it worked pretty well to solder the pieces together and then coat the joints in hot glue. Where exactly you connect each segment will completely depend on what type and size of gears you are using. I recommend placing the gears that you are using on their corresponding segments while you are connecting them in order to give the scaffold the correct structure and ensure that all of the gears will be able to run smoothly. Feel free to use the measurements in the picture above, but remember that these numbers are estimates that will not necessarily apply to your project. Just focus on the overall structure and use the gears that you have to shape it.

Once you have fully assembled the gear train scaffold, hot glue it into the center hole of the base from Step 1. When finished with this step, your project should look like the picture above on the bottom right. It is a good idea to put the gears on at this point so that you know that they fit correctly and run smoothly together. Make sure that you are able to place the motor with its gear attachment somewhere on the base so that it is able to turn the bottom gear. If it doesn't quite work, move the gear train scaffold up or down a little bit until the motor can connect to the gear assembly.

Finally, hot glue the 1" bar magnet to the bottom of the red gear on the end of the gear train so that it leaves about 0.75" between the end of the magnet and the wood base.

Gather 9 paper clips as well as the 3" x 3" cardboard square and have your hot glue gun, pliers and soldering iron (or superglue) at the ready for this step. You will also most likely need some small wire cutters or scissors to cut the paper clips.

First, take 6 of the paper clips and straighten them out with pliers as seen in the first picture above. Then, clip off the excess part of the paper clips and use pliers to bend the curved end downwards at a 90 degree angle as seen in the second picture. Your metal marble should be able to roll all the way through each of these paper clips without hindrance.

With the remaining 3 paper clips, cut them so that they look like the third picture. Then, put a slight 45 degree bend in each of them, as seen in the fourth picture.

Finally, make a small cardboard holder for the marble to rest in when it reaches the end of the track. There are no specifications for how this should be done, and it may even be best to wait until you finish building the paper clip track so that you know how large the cardboard holder should be and where it should be placed. Just make sure that the right side of the cardboard holder doesn't have a wall so that the marble can be pulled out by the magnet.

You now have all of the materials that you need to start assembling the marble track. Follow the pictures in the second and third pictures above to help clear up the following process:

First, take 1 of the first 6 paper clips and make a sharp 180 degree bend with a third of it (see the top paper clip in the second photo above). Bend this third of the paper clip above the rest of it. Take another of the first 6 paper clips and attach it to the end of the first one without bending it at all (I soldered the paper clips together, but a small amount of superglue should also work). Take 2 more of these paper clips and bend them at a slight 45 degree angle. Attach each of these to the growing chain of paper clips. Use the last 2 of these paper clips to guide the end of the chain to cardboard holder at the end of the track. As you are constructing the track you will have to make sure that it is always going slightly downwards so that the marble does not get stuck at any point.

When the paper clip track is completed, hot glue it to the metal rods and attach the end of it to the cardboard holder. If you have not done so already, hot glue the cardboard holder to the base as well and make sure that it is located just in front of the red gear. When you place the marble in the cardboard holder and spin the red gear around, it should be able to pick up the marble. Also, make sure that the magnet on the gear can drop off the marble at the top of the track when you spin it all the way around.

Finally, add the remaining 3 paper clips to the track to be used as rails. Solder these paper clips to the 3 major turning points in the track to make sure that the marble does not fall off at those points (see the pictures above for guidance). Set the marble at the top of the track and make sure that it can successfully make it all the way down the track without falling off. The force of gravity will enable it to make it all the way to the bottom.

Now that the marble run is done, the last step is to motorize it! Gather your DC motor, battery case, batteries, switch, and wire.

In order for electricity to travel from a battery and perform work in a motor or other device, it needs to travel through a complete loop. In this step, we will be using wire to allow electricity to flow in a simple circuit.

First, take the motor and hot glue it to the wood base so that the gear attachment meshes with the smallest gear of the gear train. You should also be able to hot glue part of the gear train scaffolding to the motor for some additional support.

Next, hot glue the 2 x AA battery case right next to the motor. Then, hot glue the switch onto the wood base so that it hangs off a little bit and is accessible.

Put the 2 AA batteries into the battery case. Take the two leads of the case and put each one on a different lead of the motor to test that it is working correctly. If the final gear is not turning in the correct direction, switch the polarity of the motor by changing which battery lead is connected to which motor terminal. Once you have determined the correct polarity, solder the black (negative) lead to the corresponding motor terminal. Then, cut the red (positive) lead of the battery case so that it is just long enough to reach one terminal of the switch. Solder the red battery lead to one terminal of the switch. Finally, take about 3" or 4" of extra wire and use it to connect the other switch terminal to the other motor terminal. When you flip the switch back and forth, the motor should turn on and off.

You have now successfully created a motorized marble run and learned about a variety of simple physics concepts, including gear ratios, magnetism, gravity, and electricity! I hope that you enjoyed making this project and that you will be able to proudly display it on your desk or bookshelf!