# 3D Printed Heat Engine

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## Introduction: 3D Printed Heat Engine

In this Instructable, we will be combining the powers of 3D printing and rubber bands to create an unusual engine used to demonstrate important concepts of thermodynamics.

An engine is a machine used to transform one kind of energy into another to produce work. In this project, we will be using thermodynamics to convert thermal energy into mechanical energy. This conversion will cause our wheel to begin a continuous rotation and, therefore, achieve the properties of an engine.

Normally when a material gets hotter, its molecules cause the material to expand. Rubber is different due to the structure of its polymers. When rubber is exposed to heat, it ends up shrinking in size. This interesting fact will help us harness the mechanical properties of rubber in order to create a working engine.

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## Step 1: How Does the Engine Work

We know that heat causes our rubber bands to contract while cold temperatures result in expansion. If a localized heat source is applied to a section of bands on our wheel, this change in temperature will result in the contraction of the rubber bands. The contracting will subsequently cause the ring to become lopsided. The lopsided ring will become unbalanced and the heavy side, which is opposite to the heat source, will be pulled down to the bottom. After the rotation has occurred, the coldest (and longest) rubber bands should find themselves in close proximity to the heat source. This process is continuously repeated causing a slow rotation.

## Step 2: Materials

• Four quarter sections for the outer ring (3D print)
• One centerpiece (3D print)
• One base piece (3D print)
• Two arms (3D print)
• 20 identical rubber bands
• 30 1/2" hooks
• One center shaft with a 2.8mm diameter
• Two pieces of 0.38" lamp pipe cut to roughly 7.5"
• A localized heat source: I used a heat gun but a heat lamp or other similar source would also work well.

Tools:

• A saw to cut the lamp pipe to size
• An old soldering iron to 'weld' the quarter sections together

## Step 3: Building the Base

First, we will assemble the base. Cut the pipe into two pieces of identical length. The exact length isn't important as long as it is longer than the radius of the outer circle (I chose a length of 7.7"). Lamp pipe is convenient because it comes pre-threaded allowing me to directly screw the pipe into the baseplate. As an alternative, a regular rod of similar diameter can be used with some glue to achieve a similar effect. Once I gently screwed the pipe into the base to prevent stripping, I then attached the arm pieces. The arm pieces will hold the wheel in a localized area while limiting friction. Finally, although it is completely optional, I adhered a piece of felt to the bottom. Once the base is assembled, I adjusted the arms by slightly unscrewing the rods to ensure they were perfectly level.

## Step 4: Making the Outer Ring

The outer ring is printed in four identical pieces. Although there are many ways to fuse 3D printed parts together I prefer to 'weld'. Using an old soldering iron and some extra filament I melted the pieces together creating a solid bond. During the assembly process, it is important to ensure that a perfect circle is being formed. To assist in the process, I printed a graphic to scale that I could use to check for accuracy. Just like metal welding, I found that it was helpful to first tack weld my pieces together before making a final completion pass.

Once again, any sturdy attachment method would work for this step as long as the weight around the ring is equally distributed and it can withstand the force applied by the rubber bands.

## Step 5: Attach Hooks

Once you have an inner and outer ring, the hooks can be attached to the prefabricated holes. During this process, be gentle to avoid stripping the plastic. If the holes do become stripped, superglue should be enough to hold the hook in place. As long as the weight is evenly distributed, the direction of the hooks is not important.

Some people might prefer installing the hooks before fusing the outer ring together. In doing so, any stripped pieces can be reprinted.

## Step 6: Attaching the Rubber Bands

Attach the rubber bands onto the hooks one at a time in a star pattern (like lug nuts on a tire). Following the image above, every inner hook should receive two rubber bands from individual hooks on the outer rim. Once all the bands are installed, check to be sure the inside ring is close to the center. If it appears to be off-center by a large amount, check to ensure the rubber bands are uniform.

## Step 7: Final Assembly

Install the shaft and balance the contraption on the arms of the base. Although I have found rubberbands have different levels of elasticity, check that the wheel isn't too off-balance.

## Step 8: What to Do

Being careful not to melt the rubber or plastic, apply a localized heat source close to the base of the wheel. It might take some time for bands to begin contracting or expanding. Once the thermodynamic process occurs, the wheel will start turning. It is important to note that a very slow rotation will be achieved.

Before building notes (Buyer beware)

• If you are interested in building one, I would recommend it, but a lot of patience is required for a good result.
• This engine cannot be used to efficiently harness energy.
• This process will result in a very slow cyclic rotation similar to a Ferris wheel.
• This is a neat science trick but needs perfect conditions to perform well.
• Nevertheless, it is an interesting concept to be able to visualize.

## Step 9: Files

• Graphic

### Attachments

First Prize in the
Rubber Band Speed Challenge

2 111
5 1.3K
15 6.0K

## 24 Discussions

Nice. Do you have a video?

Very fascinating idea.. - Thank you.. - I had to remodel it because of the very limited print area of my 3d-printer.. - I liked the idea of build-in dovetail connection.. - And had the idea of a build-in "hook-system". - Modelled in TinkerCad... - What do you think?

Great Idea for the hooks! I look forward to hearing how the project 'turns' out!

It might be helpful to dovetail the ends of the circle pieces. Something like this.

Yes, you are right. Dovetailing would make the whole process a lot easier. Recently I have been very interested in 'welding' parts together so that's what came to mind when I designed the wheel. If I make a version two I will be looking to make it entirely printed with no extra tools required.

Clever idea! For version 2.0, print the hooks in the ring and hub when you 3D print it. Also, print dovetail joints to connect the ring sections using the rubber band force to hold them together (like compressing a stone arch, but with 3D printed interlocking rocks). No solder/welding required.

Great Ideas! It would be cool to use the rubber band's own tension to hold the whole outer rim together. I might have to look into doing something like that. You could almost turn it into a very interesting puzzle.

excellent, I like this. Why not printing hook in 3D and directly attached to the wheel?

I originally planned on printing my hooks but I decided that the metal hooks might better for prototyping and were a little more durable. I ended up liking the pop of color so I kept them for my final product.

Did you find a good source for rubber bands? Or buy a big package and spend lots of time sorting to find 20 that were identical?

I made one with a bicycle rim a couple of years ago. It's difficult to get setup, balanced, and adjusted. But perhaps at this smaller scale this is less of an issue.

I ended up purchasing mine from target they had an assorted ‘jar’ for about \$3. There are a few different sizes so you will have to sort through to find the ones you need. The one advantage is that the different sizes will give you a chance to experiment with heat and elasticity combos to find the one that works best for you.
I would say that 3d printing helps decrease the number of balance issue you might encounter

search for "#64 rubber bands" these are a great size used frequently by the folks who fly model airplanes.

This brings back memories! I made a version of this (mumblety-mumble) years ago for a 7th grade Science Fair project using a large film reel spinning on bearings made from some sheet teflon scraps my Dad cadged from the machine shop at the company he worked for...which was pretty high-tech stuff at the time.

We've come a long, looooong way since then :-)

Good job. I built something like that 50 years ago. It was twice as big and made with wood. Half was blocked with foil and the heat source was a heat lamp. It was slower than one revolution per day...

Very cool! I like the idea of using foil to block the heat. Although this wheel goes a little faster when working properly it definitely isn't going to win a speed award any time soon.

Thank you!

Neat implementation. I've balanced bicycle wheels; I can envision it will turn very slowly (as stated).

Since I welded my frame together, I added a very minimal amount of weight to the rim which thankfully limited my balance issues (although the varying rubberbands caused some difficulties). If there is a large discrepancy in the weight, adding drops of hot glue to the outside of the wheel might be an easy way to add small amounts of weight.