Electrically Heated Ice Cream Scoop

My favorite line (and the only one I know) from the Declaration of Independence is, "We hold these truths to be self-evident, that all men are created equal, that they are endowed, by their Creator, with certain unalienable rights, that among these are life, liberty, and the pursuit of happiness." I don't know what aliens have to do with it, but in making the Constitution the Framers were attempting to prevent the crisis that the great nation of the United States currently faces. "Which crisis?" you may ask. Well, the decline in wrist health that prevents millions from “pursuing the happiness” afforded to them by ice cream. According to the U.S. Department of Health and Human Services, one in four American adults report a diagnosis of arthritis, and the progressive aging of the population will only exacerbate this epidemic. Arthritis of the wrist or hand makes it painful and difficult to scoop ice cream, necessitating a new class of scooping tool to accommodate these individuals and make scooping easier. While I don’t have arthritis, I do have weak arms and a general proclivity towards muscular laziness, so I thought I could benefit from such a device as well. As I thought about it, I realized that a heated ice cream scoop could help lighten the burden on those with arthritis and the weak-armed alike. I also figured this project would be a good way to enhance my skills with Fusion 360 and would be a good exercise in my ability to build simple circuits. Since I had so much fun making it, I figured I would share it.

This project is not difficult and is geared towards beginners, but does require some basic electronics equipment. The components are somewhat cheap, but together can be expensive. I’ve provided links to some of the components I used or similar varieties, but there could be some cheaper alternatives online. One thing that does justify the cost, in my opinion, is that these components can all likely find uses in future projects.

Tools:

• Soldering iron and solder
• Hot glue gun
• 3D printer or access to a 3D printer/printing service (some public libraries have 3D printers open for general use, and you can order 3D prints from companies like PCBWay or JLCPCB, so don’t let this preclude you from building this!)
• Autodesk Fusion 360 :)
• Pliers or a dupont wire crimping tool
• Optional: Soldering helping hands, wire stripper, heat source for heat shrink (lighter, hair dryer, heat gun)

Components:

• 3.7v 18500 lithium ion battery
• A 3.7v battery protection circuit (BMS). You can find small 18650 BMSs that work with 18500s
• 2-pin male and female dupont connectors or some similar form of solderless connection
• A small wire gauge (I believe I used 30 AWG)
• 28 AWG or similar sized Nichrome or resistance wire
• A blue LED and suitable resistor (I used a 330 ohm resistor)
• On/off switch
• Female USB-C port

The goal is to have a scoop that slices through the most icy of ice creams with ease–basically the ice cream scoop equivalent of Excalibur. Heated ice cream scoops exist already, but many are hand-heated or not battery powered. Most, if not all, are not dishwasher safe, either, which is hopefully (eventually) something that this project will address. They all also heat the entire scoop so that the ice cream inside the scoop melts excessively. To counter this, only the edge of this scoop will be heated so that you can scoop the ice cream and leave it in the scoop for a while before it melts.

In regard to the actual design, the physical scoop will look like a normal ice cream scoop, except with a hidden heating element wire under the edge. The wire I used was Nichrome 80 wire, which, from the sources I’ve found, seems to be nontoxic. Regardless, since the wire is inside the scoop, it shouldn’t come in direct contact with food. Since batteries are most definitely not dishwasher safe (don’t test this please), to clean the scoop we’ll have to remove the battery/components compartment. The plan is to fit the battery and components in the lower part of the handle, so that we can remove the scoop and upper part of the handle and put it in the dishwasher (ice cream shouldn’t get as far down as the lower part, so you shouldn’t even need to clean this anyways).

I will use a 1600 mAh 18500 battery for this project, which should give the scoop around an hour and a half of battery life (based off of extremely rough and maybe flawed current calculations). Unless you work as a professional ice cream scooper, this should be sufficient, and even if you do work as a professional ice cream scooper, you can make extra battery compartments to switch out when one runs out. While you’re using one, you can charge the others (you can also just keep the scoop plugged in). Since USB-C is all the rage these days, this is how the scoop will be charged.

To transfer power between the handle segments, I’ll use two-pin dupont wire connectors, male in one segment, female in the other.

This instructable is geared towards beginners (I’m a beginner myself), so don’t worry if you don’t know anything about design or circuits. If you do have arthritis, though, some of the finer soldering may be difficult. Since the target audience is beginners, I detail my design process comprehensively below, so if this interests you, feel free to read it. If you don’t care and just want to build the scoop, skip the physics and design section (steps 2-8).

While understanding the physics behind this project isn’t necessary, it is pretty darn cool (or hot, I guess I should say). Also, next year I’ll be starting college as a physics major, so I figured I might as well share my passion. If you hate learning about awesome things, skip this section.

Now that everyone has been sufficiently guilted into reading this, I’ll start explaining (to the best of my ability, correct me if I’m wrong) how it all works. This project uses resistance wire which heats up when electrical current is run through it. At the (beyond) microscopic level, when you connect the circuit, the electric potential, or voltage, between two points of the conductor, or the resistance wire in this case, creates an electric field. This shoots electrons through the conductor, which collide with atoms. Since the electrons have kinetic energy (they’re moving), when they collide they transfer some of this energy into the atoms (they make the atoms move more). Since the temperature of the wire is just a measure of the average kinetic energy of its atoms, this makes the wires slightly hotter. Since a lot of these collisions are happening, the temperature increases rapidly until it’s hot enough to scoop through ice cream easily! 

The following equation shows what’s going on. It’s called Joule’s first law. Simply, it’s:

Q = I^2Rt

Q = Heat (Joules)

I = Current (Amperes)

R = Resistance (Oms Ω)

t = Time (seconds)

All this means is that heat increases when there’s more current, resistance, or time the current has been applied to the circuit. Since nichrome wire has a really high resistance, it is good at creating heat.

Hypothetically one could use the equation Q = mCΔT, where m is the mass, C is the specific heat capacity of the material, and ΔT is the change in the temperature in celsius, to calculate how much the wire would heat up. You would have to account for the change in resistance due to heat, though. If you calculate this, or if you discover that it’s not even possible to use this equation in this context, let me know in the comments.

Nichrome wire has a high melting point, so it can get red hot (not in this project, though, so don’t worry). When it heats up, it forms a layer of chromium oxide which protects the rest of the wire from further oxidation, making it an ideal heating element material. It’s used everywhere, from fireworks to e-cigarettes to aerospace applications.

At first glance, an ice cream scoop appears to be a difficult shape to design. Anything is possible with a good CAD software and some patience, though, so I wasn’t worried. I also knew that Fusion 360 has a rotation function that allows you to revolve sketch objects around an axis to create solid bodies. Since an ice cream scoop at its base elements is just a hemisphere attached to a circular handle, I thought this function would be perfect.

It’s also worth noting that it is always a good idea to adhere to the principle of parametric design, which Fusion 360 makes easy. Simply click on Solid → Modify → Change Parameters. These act as variables, or placeholders, for a value. Instead of typing in an unchangeable value as a dimension, you can input these and change them later if necessary. If you end up disliking the design once you print it, or if you discover that the components don’t fit, parameters make redesigning easy.

Since a good 3D design always starts with good 2D components–sketches–I started with designing the scoop sketch, drawing two ellipses centered on the origin with a central vertical axis (I opted for ellipses because I liked the look of an elliptical scoop rather than a simple hemisphere). The distance between these is the thickness of the ice cream scoop. Since the scoop must be sturdy, 2 millimeters is a good value for this. 

Now, by rotating the shape made by the space between the inner and outer ellipses 180°, you get an ice cream scoop shape. Since eventually we’ll thread a resistance wire through the scoop, we need a tunnel around the edge. To make this tunnel, I created two more ellipses within the space between the first two, and simply extruded the new inner shape a certain distance into the scoop itself. While this may have caused the wall in some places to become very thin, it ended up printing fine and is still structurally sound. Performing a two-sided extrusion can let you fill in the gap at the top.

I needed to get the heating wire into the scoop somehow, so I decided to make the scoop completely separate from the handle but able to join it once I got the wire in. Thus, I needed a section of the scoop to serve as a coupler with the handle. This meant I now had to design the handle before continuing with the scoop.

I wanted a tapered handle design, which ended up being easier than I originally thought it would be. I started by creating a line centered on the origin. This is the width the taper begins with. I then extended a line from the origin to the end of the handle. I then created another line centered on this line’s midpoint. This is the width the taper ends with. I connected the endpoints of the new line to the endpoints of the beginning line. This gave me a general handle shape, which I rounded off with a circle centered on the end of the handle length line. After revolving this, the handle looks pretty good. Make sure it forms a new body. It’s not hollow yet, but this can be easily remedied. When I designed it, I drew a secondary line from the end of the handle to the beginning offset a little from the edge. This allowed me to revolve the inner region to hollow out the handle. In retrospect, using Fusion 360’s shell feature would have been much easier. It can be found under Solid → Modify → Shell. Click the handle and set the wall thickness to your specified value. Two millimeters works well to create a sturdy handle with enough room for the components. If it’s not working, try tweaking some of the options. If it still doesn't work, you can manually draw another line to serve as an inner boundary, and just revolve the inner part to hollow out the handle. This is what I did, because I discovered the shell feature after completing this part of the design.

To make the coupler, create a line along the handle sketch at the desired length for the coupler. Don’t make it too long, because we still have to fit some components in the handle. Create points a millimeter from both edges on the beginning line and the new line you just created. Connect the points with lines. Revolve the inner space to create the scoop’s side of the coupler. Then revolve the inner space again to cut a section out of the handle that will allow the scoop to conjoin with the handle.

One difficulty is figuring out how to actually get the wire into the tunnel. We need an opening somewhere, and since the heating wire receives power from the battery in the handle, this opening must have access to the handle. I began by adding two squares the same size as the wire tunnel onto the original scoop sketch spaced apart a little. I then just extruded these downwards until they cut through the space inside the coupler. I filled in the space between these rectangles. Now comes the most difficult part. To make it easier to insert the wires, I filleted the upper and lower edges of these new downward wire tunnels. This made it somewhat rounded, although the filleted edges weren’t perfect. There is definitely a better way to do this operation, I’m just not skilled enough with Fusion 360 yet to figure it out. It requires some laparoscopic maneuvering to enter the wire tunnel, so instead I just sliced the scoop apart in a couple of places to gain access to the inside.

When I first printed my ice cream scoop and tried to put the heating wire through, I couldn’t fit it into the holes–the coupler just got in the way too much. So, I figured that it was necessary to cut a small section out of the scoop and coupler (last image). This would allow me to feed the wires through the scoop and the new section before putting the section in its place and threading the wires through the coupler and into the handle. This ended up working well, and to do this was relatively simple. I made a new sketch and drew a rectangle the same size as the area I wanted to cut out, using it as a splitting tool to cut the scoop. You can do this with the Split Body tool. The only problem is that this creates three bodies. To fix this, I used the Combine tool to conjoin the scoop and the other, unneeded body.

Now, finally, the scoop is done!

Which leaves us with the handle…the most difficult part. We need to add ports for various components (USB-C port, LEDs, button, dupont connectors) and make the handle modular.

Since we need to eventually put components in the handle, we must first split the handle horizontally for easy access to the inside. To do this, create a sketch at the very end of the handle. This will also be the sketch we use to make the USB-C port and the places to put the LEDs. Make a circle, with a diameter of the end taper width. Draw a horizontal line to use as a splitting tool. Split the handle, making sure to toggle the visibility of the scoop off so that you don’t accidently cut this as well.

While we’re on this sketch, we might as well design the USB-C and LED ports. Centering it on the centerpoint of the circle, draw a center rectangle with the following dimensions (wow, that was a lot of centers): a width of 9.4 millimeters, and a height of 3.4 millimeters. This should give you plenty of clearance in the case of an inaccurate printer. Mine is extremely inaccurate, so it may even give you too much allowance, which is why you should make these into parameters that can be edited later. Next, filet each corner of the rectangle with a radius of 1.25 millimeters. Make this a parameter as well. USB ports are always some of the hardest parts of a design to get right. It’s surprisingly difficult to find the right dimensions online, so these values mostly come from some handy digital calipers and trial and error. You can also draw another rectangle around the USB-C port to serve as a place to put the glue that will keep the port in place. Extrude the USB-C outline so that it cuts into the handle, and extrude the other rectangle (with the USB-C port cut out) in a join operation into the handle as well. I extruded mine 10 millimeters and it worked well. (One note: you can make extruded values negative to switch their directions). Don’t worry if a part sticks out of the handle, we’ll fix this later.

Next up are the LEDs. These are optional, but a good idea to have. If you choose to put them in, we need an LED to indicate that the scoop is on, and one to indicate the state of the battery when it’s charging. Most rechargeable battery boards don’t have a place to add either LED, so we’ll have to integrate them into the circuit we make. I couldn’t figure out how to add the latter LED without microcontrollers or other complex parts, so I dropped it from my circuit design. I still added it to the handle design, though, in case I wanted to add it in the future.

I have 3 millimeter LEDs and 5 millimeter LEDs. Either size will work, but the 3 millimeter ones will leave more space for wires and components. For this reason, I decided to go with the smaller size. On the same sketch containing the USB-C port, create a two-point circle. Place the first point on the midpoint of one of the shorter sides of the USB-C port (the midpoint may be difficult to find, as the shorter sides of the USB-C port are quite small, but you just have to zoom in a lot). Place the second point a certain distance away, taking care that the line you are making is straight. You want the diameter of the circle to allow for the size of the LED and its enclosure. A 7.5 millimeter enclosure worked for me, but this makes the wall of the enclosure 2 millimeters thick, which is excessive. The other 0.5 was to make sure the LED fit in its enclosure. 1 millimeter walls are enough, so if you’re using a 5 millimeter LED, 7.5 is still a good value. In the center of this circle, draw a circle with a 1 millimeter diameter. If your printer is very inaccurate, or if you’re printing the handle with its base on the build plate (which I’d recommend), you may want to increase this to 1.5 (printing the handle base-down can cause first layer squish, which could mess with the LED aperture’s diameter). Repeat this process on the other side, or use the Mirror function, if you want another LED. To mirror, you’ll need a line to reflect over, so draw a vertical line from the bottom of the circle to the top. This line will come in handy later, as well.

Extrude the LED aperture holes all the way into the handle. Extrude the enclosure a certain distance into the handle that will allow for the LEDs to fit inside the enclosure without falling out. 10 millimeters worked for me. Again, don’t worry if part of the enclosure sticks out beyond the wall of the handle, this will get fixed later. You can definitely leave the LED enclosures like this, but if you wish, you can do a double sided extrusion with the inner circle to make the front wall of the enclosure flat. Just make sure the distance between the outer handle wall and the inner LED enclosure wall isn’t too thin.

Good job making it this far, we’re close now. All we need is to design the button enclosure and the coupling mechanism between the parts of the handle. Let’s start with the button.

First, we must create a plane off of which we can draw the sketch for the button’s enclosure. Use the Plane Along Path tool in Solid → Construct, and select the vertical line we made earlier in the USB-C and LED sketch. Drag the arrow all the way to the top of the circle. This should create a plane on top of the handle. Create a sketch on this plane and make a construction line extending into the handle (there’s an option for a normal line or a construction line in the line editor popup, pick construction line). The beginning point of the line should start at the plane’s origin (there should be a point here that your cursor snaps to), and the endpoint will be the center of the button’s enclosure. I found that 23 millimeters was a good length.

Next, create a center rectangle on the line’s endpoint. The width of the button I used was 18 millimeters, and the length was 12 millimeters, so if you use the same switch make the dimensions of the rectangle accordingly. Making another center rectangle will help create the walls for the enclosure. You can make these walls as thick as you want, but I made mine 2 millimeters. 1 millimeter will work just fine, though, and may give more space for wires when we put the components in. Whatever thickness you choose, double it and add it to the width and length of the first center rectangle you made. Next add a space for the actual button. This can be a small square button, a large circular one, or whatever you want. This is because the actual part we’ll press will be printed and glued onto the switch button, as the switch’s button is too recessed to comfortably press once it is inside the handle.

The button has two tabs that you connect the wires to on both of its short sides. Because of this, we’ll have to create an additional two rectangles to allow for these (they come with the tabs folded out, but once you fold them in they still stick out a little). These rectangles don’t have to be too long, and make them as wide as the enclosure walls. Finally, make another rectangle on the long side not facing the USB port. Make this around 10 millimeters long and the width of the enclosure wall. This will help secure the positive battery terminal.

Extrude the space between the inner and outer rectangles, deselecting the two rectangles we made to allow for the button’s tabs and the rectangle for the battery terminal. 12 millimeters was a good value for me. Extrude the battery terminal rectangle an additional 6 or so millimeters, for a total 18 millimeters. Any more than this and it could eat up too much space for the wires once the components are in. Toggle the visibility of the lower handle off, and use the button cutout as a splitting tool to cut it out of the handle.

The final task we have is the handle coupler. We first need to split the handle in half. To do this, first create a new plane along the vertical line we created for the USB port sketch. Drag the arrow halfway down the line, or set the value for the plane to 0.5. This should create a plane that perfectly bisects the handle. Create a sketch on this plane, and draw a line from its origin along the length of the handle. The length of this line will be the length of the battery and components portion of the handle. 75 millimeters was originally a guess on my part, but ended up being perfect for the battery and all the components. Make a perpendicular line at the endpoint that extends beyond the boundaries of the handle. Next, use this as a splitting tool to cut the handle into two parts.

Create a sketch on the new face created by this split (the cross-section of the handle’s walls). Determine a good diameter for the coupler (I used 15 millimeters), and draw a circle with this same diameter centered on the center point of the handle cross section. We need a cutout to put the dupont wires, so make a center rectangle in the middle of the new circle. The dimensions I used were 5 (width) x 2 (height) millimeters.

Since the dupont connectors must line up when the two handle parts are joined, we can’t have the coupler be completely circular. The user could try to connect the coupler in the wrong orientation and potentially bend the male dupont pins. To avoid this, I added an additional rectangular piece to the top of the coupler. This makes it impossible to put the two handle pieces together incorrectly. To do this, place a point at the top of the circle. While you’re at it, place points on the bottom, left, and right sides of the circle. Next, draw a center rectangle at the top. The part that sticks out beyond the borders of the power coupler will be the “rotation lock,” so make sure this part is tall enough to stop the user from sliding the handle pieces together with a wrong orientation. I used a width of 5 and a height of 2. With these dimensions, the minimum height of the rotation lock above the main coupler body is 1 millimeter.

We also need a way to lock the two handle pieces together so that they don’t simply slide out. One way to do this is by making the battery side have small elevated rectangles that are slightly bigger than corresponding holes on the scoop side. This should create a tight, but removable union between the two handle parts. So, centered on the points you made on the bottom, left, and right, create center rectangles with widths of 2 millimeters and depths of 1 millimeter. These small values should allow the parts to mesh but still be sealed once the handles are connected.

You may have noticed at this point that, once we extrude the coupler, it will just be floating in the middle of the handle. You’re right, so first create another circle bigger than the cross section, which we’ll use to fill in some gaps.

Now it’s time to extrude the coupler. Let’s first start with the battery side. Select the larger circle you just made and everything inside it, except for the rectangle at the center of the sketch. Extrude it into the handle 2 millimeters or so. Don’t worry if the circle juts out beyond the handle’s walls. We’ll fix this eventually. Next, select every part of the coupler sketch you just made except for the smaller rectangles meant for locking the pieces together and the larger outer circle you made. Extrude your selections to whatever length you want the power coupler to be. I chose 20 millimeters. Now, select the smaller rectangles and extrude them, using the “two-sided” extrude option. For the first value, input the length along the power coupler that you want the rectangles to be. Keep in mind that these smaller rectangles will cause resistance when the user is sliding the handle pieces together, so if you put them closer to the beginning of the power coupler, there will be less total resistance. For the second value, input the first value minus whatever width you want the rectangles to be and finish the extrusion. I input this value as 2 millimeters. To make it easier to slide the parts together, filet the front and back edges of these rectangles.

Now, the component side of the handle should be completed. To finish the scoop side of the handle (and the last part of the design), use the same large circle (deselect the inner center rectangle again) from the previous sketch to fill in the first part of the handle. The length of this extrusion should be the length of the power coupler plus a little extra for a place to put the male dupont wires. In total, the extrusion I performed was 30 millimeters into the handle. Make sure this is a "join" extrusion. Next, select the power coupler circle and rotation lock and extrude it to cut into the newly filled in section. Make the length of this extrusion the same length as the power coupler. Now, all we have left is the holes for the additional locking rectangles! To make these, select the three locking rectangles and perform another two sides extrusion. Input the exact same values as before. To make these holes slightly smaller, perform extrusions or “press pulls” (Solid → Modify → Press Pull (Q)) to bring the edges of the holes a little closer in. Don’t be too liberal, though, because it could cause the locking rectangles not to fit at all.

Congrats! At this point you’re pretty much done with the design! You may notice, though, that all the operations we did caused the handle parts we split to join back together. This can be easily remedied by splitting again, or just dragging the split history marker to the end of the timeline (the little thing at the bottom of the screen). You are also probably wondering how to get rid of all the parts jutting out of the handle. I’m fairly sure you can just select these faces and delete them, but in case you can’t, do the following: edit the original handle sketch and draw a rectangle that is larger than the handle. You can then revolve the part of the rectangle that is outside of the handle boundaries to shear off the additional parts.

Now is also a good time to review the design and add clearance allowances according to the specifications of your printer. My printer is very bad, so I had to make these really large. 0.2-0.5 millimeters usually works, though, and it is a good idea to apply clearance allowances wherever there are parts that have to mesh together (including with the components). Add these wherever you see fit. Extruding works for most of them, but press pulling usually works for the more irregular faces. Making these clearance values parameters makes it easy to change them later if they don't work.

Now, finally, the design is done and the building begins!

P.S. One note. If you are ever stuck on any of these steps, Autodesk has a great Fusion 360 forum to troubleshoot problems with the community. Also, there are a ton of online tutorials, including some made by Autodesk. If you’re really stuck, you can also post a comment so that I can help guide you through. If any operation is not working for you, there are usually at least two ways to do something, so try doing something else.

P.P.S. Writing this, I’ve realized that there were easier ways I could have done some of these operations. I am currently in the process of making a smoother, simpler version of this design that may be easier to understand. In the future, I may update this instructable or post a new “version 2.0.”

The 3D printing for this project isn’t too much of a commitment, as it requires neither a lot of time nor a lot of material. I found that the handles prints look the best and perform the best printed with the open parts facing the build plate. For FDM printing, use tree supports, as they will be easiest to use. Print the scoop with the open side facing up and away from the build plate. Print the additional scoop part and the button in whatever orientation you want, but I printed the scoop part on its side.

My 3D printer is a slightly upgraded Ender 3, and just before I printed the final parts I ran out of PLA filament. I had to use PETG, which my printer could not handle for some reason, so please excuse the print quality of my project. I didn’t have time to fix my printer before I went out of town for an extended period of time. I do kind of like the final appearance of it, though, and post-processing can always fix the worst blemishes.

A note on food safety: 3D prints are NOT food safe. Do not try to use these 3D prints in their raw form to make this ice cream scoop if you plan to use it for food you will injest. There are processing methods and even printing methods that can create food safe and dishwasher safe 3D prints, but traditional methods will not. Review this article for a comprehensive review of 3D print food safety. The end goal of this project is to make molds and make the scoops out of some sort of durable, food safe, and dishwasher safe resin.

The circuit for this project is pretty simple, thankfully. A 1600 mAh 18500 3.7 volt rechargeable lithium-ion battery provides the power. It must be protected by a battery protection circuit (BMS (battery management system)), which prevents the battery from overcharging or over discharging (basically it prevents it from exploding, which is nice of it). The BMS is connected to a USB-C female port for charging. The output is connected to an on/off switch and an indicator LED to show the user if the scoop is hot or not. The on/off switch is connected to dupont connectors, which allows for connection to the resistance wire. The above diagram shows this (sorry electrical engineers, it’s not in the standard format. I thought this would be confusing for beginners).

The polarity of the dupont connectors doesn’t matter, so don’t worry about this. The circuit diagram for the scoop part of the handle is pretty simple, so I didn’t draw it up. Basically, connect the terminals of the heating wire to the dupont connectors. I never tried to put the heating wire directly in the dupont connector, but this would probably be fine. It would also eliminate the need for solder, which could create toxicity issues if it is washed in the dishwasher (I’m not sure but I would assume. If you’re going to risk it, definitely don’t use lead solder).

A note on heat shrink: Heat shrink is a sheath you can buy that shrinks around wires when exposed to heat. It’s useful for protecting bare wires and solder joints, and may be especially important for the battery terminals in this project. One consideration, however, is that it limits the wire flexibility, which is important for the project. For this reason, I didn’t use it on every joint, and instead relied on the incredible insulating power of hot glue.

Begin by soldering two wires to the positive and negative battery terminals. Using red and black wires helps with organization. I used red for positive and blue for negative, since I didn’t have black. In this case, the negative wire must be much longer than the positive wire, but make sure neither are too short or too long. When in doubt, measure your wires roughly by looping them around the enclosure in a rough approximation of their final positions. I used the spring piece as the negative terminal and the flat piece as the positive terminal. Next, solder the end of the wire attached to the positive terminal to B+ on the BMS, doing the same (but opposite) with the negative terminal’s wire.

Next, twist two short red wires together and solder them to P+. Connect one of them to the USB port’s V, and the other to one of the switch tabs. Next, twist two short black wires together and one long black wire (make it long enough to stretch across the entire battery compartment). Solder this to P-. Solder the two short wires to the USB port’s G and the negative LED pin. Leave the longer wire for now.

Next, twist one short red wire and one long red wire together (long enough to stretch across the whole compartment) and solder them to the other switch tab. Solder the shorter wire to the resistor. Then solder the other resistor pin to the positive pin of the LED. This should be the last of the soldering.

Crimp the two longer, unconnected wires into female dupont connectors. Be careful, though, this is hard at first. I had to practice 3 or so times before I could get it right, and I watched this video beforehand. Once you’re done, put these wires into a 2 pin female dupont enclosure. Repeat this for another two wires (if you don’t just put the resistance wire straight into the dupont connectors). This will be for the scoop side of the handle. If you didn’t use the raw resistance wire in the dupont connectors, solder or connect in some other, more food-safe manner, the ends of the dupont connector’s wires to the ends of the resistance wire.

*I used a hot glue gun for all this, which worked well.*

Grab the side of the handle with the button enclosure on it. First glue the negative battery terminal to the side closest to the handle coupler. Glue the positive terminal to the part that juts out from the button enclosure. Take care not to tangle any wires, and don’t use too much glue. This could cause there not to be enough space for the battery (it’s a tight fit). At this point, you can test if the battery fits, making sure that you don’t reverse the polarity of the battery by accident by placing it in the wrong orientation. At this point, check that the led works as well. If it does, it’s likely the project is a success! If it doesn’t, don’t despair. Failure is a part of any engineering project, and it’s what leads to growth. Edison failed 1,000 times before creating the lightbulb, so if you fail once you’re still a better engineer than him (I think this project is a great comparison to that, if not harder, right? ;).

If it fits, you can move on to gluing the other components in place. Fit the switch in and glue it down, doing the same with the LED and the USB port. If you didn’t put heat shrink on the LED pins, make sure they are short-circuiting (touching) before you glue them. If they are, just manually move them apart and put glue in between.

Next, fit the battery in. You may need to rearrange the wires attached to the battery terminals. There should be a little space in between the battery and the edge to fit the BMS in. Stuff it in that space, or any space available, and glue it to the side of the handle, not the battery. Finally, loop the dupont wires around the battery and into the space we made for them, making sure that the holes are flush against the outside of the handle coupler.

Now, try to fit the top part of the handle over all the components. If it doesn’t fit, check for wires sticking out around the edges, or rearrange the inner wires so that they are compact and away from the edges. When they are sufficiently contained, put a little glue around the entire edge and on the USB port and the dupont connectors (not too much glue on these last two, though. I made this mistake, and there was a big glue gap between the handle sides in my finished project). Press the halves together and hold it for about a minute. 

Glue the button print to the actual switch, being careful that you don’t accidentally glue it to the side of the handle, rendering it un-pressable. Test the strength of the glue seal, and move on to the lower handle.

Glue the male dupont connectors into the provided space like with the other side of the handle. Liberally apply glue to the scoop coupler and slide it into the handle. Make sure it is firmly connected. Next, put glue around the edges of the lower handle prints and press them together for a minute or so.

Test that the duponts connect well and that the scoop heats up when the button is pressed. If it does…

You’re done! Congratulations! You now have a working heated ice cream scoop. I hoped you learned a lot and enjoyed the build, now happy scooping!

Notes on the scoop's performance: Sadly, I did not get the chance to test the scoop on real ice cream before I left on a family trip. That being said, when you turn the scoop on, the edge gets quite hot, maybe even too hot. Considering that other heated scoops claim to cut through ice cream well with a fraction of the temperature that this scoop reaches, I expect that the scoop shreds through even the most frozen ice cream easily. Truly a victory for the arthritis victim and the weak-armed alike! If you find that the scoop does get too hot, you could try a larger resistance wire gauge, or you could also try adding resistors of different values to reduce the current that passes through the scoop. I haven't tried this, so I don't know if it works, but I assume it would.

This one's self-explanatory...