Spintronics: Build mechanical circuits

Spintronics is a new game (ages 8 to adult) from the makers of Turing Tumble where players build mechanical circuits to solve puzzles. Players feel the pull of voltage and see the flow of current as they discover electronics in a tangible and deeply intuitive way, using the first physical equivalent of electronics ever built. It’s fun, fascinating, easy-to-learn, and irresistible to play.

Electronics is the foundation of modern technology, but it’s an especially difficult subject to understand. That's because it's so abstract - it can't be seen or felt - so we have to rely on advanced math to understand what’s happening, putting it out of reach for kids and most adults. That’s so unfortunate because there are few subjects as naturally compelling as electronics. Electronics is about bending raw energy: splitting it, storing it, multiplying it, reversing it, and shaping it to your will.

Spintronics lets you experience electronics in a relatable way. Instead of electrons flowing through wires, chains flow through circuit components like mechanical resistors, capacitors, inductors, transistors, and switches. Players build all sorts of crazy contraptions, and in the process, they discover important electronics concepts. Even many advanced concepts become obvious when you play with them in mechanical form. You'll never see electronics the same way again.

Kids and experts alike will discover the fun of electronics without any, well, electronics!

Spintronics comes in two parts: Act One and Act Two.

 Spintronics Act One includes:

Spintronics Act Two picks up where Act One leaves off. (Note that the parts from the Act One kit are required for Act Two.) It includes:

The Spintronics Power Pack is an expansion kit that gives you parts to charge your circuits with more power, along with a puzzle book including 10 additional puzzles.

 Spintronics Power Pack includes:

Players place spintronic components onto the magnetic base tiles and string chain between the parts to make circuits. There are eight different spintronic parts:

The spintronic battery powers your spintronic circuits. It pushes the chain with a constant force (voltage). Charge the battery by pulling the string. A built-in mechanical circuit breaker automatically shuts it off in the event of a short circuit.

The spintronic inductor builds momentum. It's heavy, so it takes a lot of energy to get it moving, but once it's going, it doesn't want to stop!

The spintronic capacitor stores energy like a spring. It also doubles as a spintronic voltmeter. The gauge on top indicates the voltage across it.

The spintronic junction allows the current to branch, just like an electrical junction of three wires. Each sprocket is one of the three paths for current.

The spintronic ammeter lets you hear the current. The more current, the higher the pitch. 

The spintronic transistor is a voltage-controlled resistor. The higher the voltage on the top sprocket, the lower the resistance of the bottom sprocket.

The spintronic switch opens and closes circuits. Push it once to open the circuit. Push it again to close it.

The spintronic resistor resists the flow of current.

With Spintronics, you can build the mechanical counterpart of practically any electronic circuit. The simplest circuit is a resistor connected to a battery:

Now let's add a second 500 Ω resistor in series with the first resistor. You can see the current is half what it was because the resistance is twice as high. Watch what happens when I stop one of the resistors with my fingers:

And now we'll use a junction to put the two resistors in parallel with each other. Watch what happens now when I stop a resistor with my fingers: 

You can also build more complicated circuits. For example, here's a "relaxation oscillator." Two spintronic transistors flip each other on and off in turn:

The puzzle books of Act One and Act Two weave progressively more challenging puzzles into a beautifully illustrated comic story in which you become Natalia, the daughter of master clockmakers from the 19th century. 

When Natalia's parents are forced to leave the clockmaking business and move to a small, dreary town, Natalia recreates her parents' old clockmaking shop in their dusty shed and spends every evening tinkering until the lamp runs low.

In a time before electricity powers the world, Natalia stumbles across an alternative technology that could revitalize the town - and change the world. Your job is to help her build increasingly sophisticated spintronic circuits to meet ever-more-challenging needs of the town.

The first challenge is shown below:

To solve the puzzle, you begin by building the starting setup just like the drawing: 

The objective tells us that we need to figure out how to make it run slower. Well this one's not too tough. We'll just put the 1000 ohm resistor in the circuit, too. Then two resistances will add together, making it run slower.

Success! It runs slower. The objective is complete and we can move on to the next puzzle.

Hold on a second...there's more than one way to solve this puzzle. Can you think of an alternative solution?

That works, too! Most puzzles have multiple solutions, just like there are multiple ways to build the same electronic circuit.

This puzzle was simple, but they get much more challenging as you progress. For example, in this intermediate puzzle from Act One, the goal is to build a circuit where the ammeter makes a high pitch noise when the button is pressed and a low pitch noise when it isn't. 

Don't worry if you can't solve this one, yet. Once you've worked through the preceding puzzles, it will make a lot more sense.

Even after making two puzzle books, I've only scratched the surface exploring what it can do. Spintronics has its limitations, but they won't stop you from creating all kinds of interesting and important circuits. If you take any electronic circuit, you can probably build the spintronic equivalent, though you will most likely need to change the part values.

Below are a couple more examples of spintronic circuits. The first is probably the most prevalent circuit in the world: the flip-flop. The voltmeter on the bottom-right shows the output.

Digital circuits like these aren't a challenge for spintronics, but analog circuits are the real test, where every little imperfection affects the circuit's function. Oscillators are particularly challenging as they require the resistance, capacitance, and inductance to all be just right. This is one of many oscillators you can build with spintronics.

There's nothing like having the physical spintronic components in front of you. It makes circuit building far more intuitive. But if you're already comfortable with electronics and want to give spintronic circuit building a test drive, you're welcome to try out our online spintronics simulator.

The Gigavolt pledge level includes Turing Tumble. Turing Tumble is our first product. In it, players discover how computers work as they build mechanical computers powered by marbles. If you pledge at the Gigavolt level, we will ship Turing Tumble two weeks after the Kickstarter, and the Spintronics kits will ship later, once they are produced.

When I set out to make a physical analog of electronics, I first had to choose between replacing electricity with a fluid (water or air) or somehow making a mechanical analog. I decided to use fluids first. That's because at junctions, the material flowing through a circuit has to split. Some of the current goes down one path and the rest goes down the other.

That's easy to do with a fluid, but how can you do it with a chain, or a belt, or with gears? At the time, I couldn't think of a way.

Between water and air, I chose to use air. Water could work, but the tubes carrying the water must be relatively large or they generate a lot of resistance. Water is also messy. I started by designing pneumatic transistors, capacitors, and resistors, and eventually built this little ring oscillator:

And after many, many tries, I even built a pneumatic inductor:

But there were serious problems with air circuits that I just couldn't get around. First, it's extremely difficult to make good seals in moving parts without adding an unacceptable amount of resistance. Second, when air is compressed and decompressed, it loses an awful lot of energy to heat, so air circuits are extremely inefficient. But most importantly, you can't see air (or water) running through tubes, so you still can't see the circuits running!

I stepped back and reconsidered a mechanical analog. But how can you make the equivalent of a junction with belts or chains or gears? How can a belt be made to flow like electricity?

Eventually the solution hit me: a differential gear arrangement. Differentials can be set up so that the speed of one gear equals the sum of the speeds of two other gears. Perfect! Even better, planetary gears (a type of differential) put all three gears parallel to each other. I made my first prototype (A). 

Hundreds of prototypes later, I arrived at the final prototype (J). Of all the spintronic parts, this was the most difficult to create. The main challenge was in making its resistance as low as possible, even while under load. Spintronics is analog circuitry, after all, and every imperfection changes the behavior of a circuit. I ended up using three bearings in each junction, and I had to create special planetary gear profiles to make the sprockets turn smoothly under a range of conditions.

At first, I used an Ultimaker 3 for all of my prototyping, but the gears needed a level of precision and surface smoothness that 3D printers can't achieve. Eventually, I got a PocketNC, a small 5-axis CNC mill, and used it to CNC mill the gears and several other parts. It worked perfectly.

The spintronic battery was another especially complicated part to design. The final version is made of 48 pieces.

I discovered quickly that a circuit breaker mechanism is essential. Without it, the battery destroys itself whenever there's a short circuit. I designed the circuit breaker like a seat belt mechanism - if it gets going too fast, a flyweight pushes a pawl into a ratchet gear, stopping it.

Resistors were tricky components to design, too, but for different reasons. A resistor needed to have constant friction, but no "stiction." Stiction is the initial, extra friction when you start moving something over a surface. For example, if you drag your finger along a surface, it takes a little extra force to get it going at first.

The solution was to create friction with a viscous liquid. When the resistor turns, it rotates a cylinder immersed in a viscous liquid. The shear creates friction without stiction. I needed a viscous, Newtonian fluid, and found that silicone oil works exceptionally well. It's also non-toxic. In fact, it's one of the main components of Silly Putty.

The other spintronic parts also went through many iterations. For example, here are some versions of the spintronic transistor,

the spintronic ammeter,

the spintronic capacitor/voltmeter,

the spintronic inductor,

and the spintronic switch.

You might have noticed that early versions of the parts have pulleys rather than sprockets. I originally used stretchy belts to connect parts together. But when I started building complicated circuits with them, I discovered two big problems:

1. A resistive pulley turns slower than the pulley driving it. The diagram below shows how a stretchy belt compresses on one side of two pulleys and stretches on the other. This causes the resistive pulley to turn at a slower rate than the pulley driving it.

2. Poor efficiency. When rubber stretches, it heats up. When it compresses, it cools down. That heat is lost to the surrounding air almost immediately. So when a section of the belt travels around the pulleys, it stretches on one side and heats up, but it loses the heat to the air, so it can't give all the energy back when it travels to the other side and compresses again. I measured a 15% loss of power at each belt. With such poor efficiency, 50% of the power was lost over only 4 connections.

I tried a wide variety of belt materials, but eventually stepped back and replaced belts with plastic chains. It was a big change, but it solved the problem.

In this section, we'll dive a little deeper into spintronic circuits and how they relate to electronic circuits. There is an awful lot that could go here, so I'll limit it to the basics. I'll add more as questions arise.

Spintronic circuits and circuit diagrams

We'll start by looking at how spintronic circuits relate to the circuit diagrams you're used to seeing. The key is to remember that all circuits, no matter how complicated, are just loops. Here's the basic spintronic circuit of a battery and a resistor (A), along with two equivalent circuit diagrams (B and C):

In spintronic circuits, the battery pushes chain into the circuit on one side (red paths) and the same amount of chain returns to the battery on the other side (green paths). In the picture above, the green paths would conventionally be called "ground." (But just like in electronics, the point you choose to call ground is arbitrary.)

That's pretty straightforward, but what about a little more complicated circuit? The circuit below has a junction that splits the current two ways. A1 shows the current leaving the spintronic battery and splitting along two paths at the junction (B1 and C1 show equivalent circuit diagrams.)

Before current can return to the battery, the two paths must join back together. In spintronic circuits, the paths rejoin at the same junction that split them.

Even in much more complicated circuits like this next one, it's always the same: the current leaves the battery, splits up and does a bunch of interesting things, and then rejoins before returning to the battery.

Where is ground?

Like electronics, it's wherever you want it to be. But the most practical place for it to be is anywhere there is zero force (i.e., voltage) on the chain.

Limitations of spintronics

In theory, you could build the spintronic equivalent of any electronic circuit, though in the current implementation of spintronics, there are some important limitations. Spoiler: spintronics won't replace the electronics that power your home anytime soon.

One major limitation comes from stray inductance and capacitance, which limit you from building high frequency circuits. But perhaps the biggest limitation is that there is a limited dynamic range. For example, while you can find electronic resistors with values from microohms (10^-6) to teraohms (10^12), spintronic resistors are currently only available in the range of 50 ohms to 5,000 ohms. 

Then, of course, there's the size of the components. Spintronic transistors are about half the size of the first vacuum tubes from the early 1900's, but about a billion times larger than the transistors in your computer.

Despite these limitations, you'll be surprised at how much you can do. You can take most circuits and build equivalent, working circuits in spintronic form.

Advantages of spintronics

Obviously the biggest advantage of spintronics is that it makes electronics tangible. There's nothing else like it. But there are actually some useful things that can be done with spintronics that aren't nearly as easy with electronics. For example, you can generate a negative voltage simply by placing a part on the outside of a chain loop. A positive voltage becomes negative voltage just like that!

It's also exceedingly easy to trade voltage for current or current for voltage, as a transformer does. Simply tie the top two sprockets of a junction together and it doubles or halves the voltage.

Spintronic transistors are also easier to use. Spintronic transistors behave like field-effect transistors (FETs) where the resistance of the source-drain depends on the voltage at the gate.

But the advantage of spintronic transistors is that the gate is isolated from the source-drain. So it's simply the voltage across the gate that controls the source-drain resistance. That makes it significantly easier to design and understand transistor circuits. Of course, if you want to emulate an electronic FET, you can always use a junction to tie the source to the gate.

Spintronic units

Finally, let's take a look some of the math behind spintronics. Spintronics introduces the mechanical equivalent to units of voltage, current, capacitance, etc. To distinguish between the electronic and spintronic units, we add the word "spin" out front. So "volts" become "spin volts," "amps" become "spin amps," "farads" become "spin farads." Also, the abbreviations of the units have a little spinning arrow over the top:

The derivation of these units comes from one key relationship that ties all of electronics to spintronics. The relationship is this: 

1 spin coulomb = 10 meters of chain

What does that mean? Well, the coulomb is a unit of charge equal to 6.2415090744×10^18 electrons. Therefore, in spintronics, we say that 6.2415090744×10^18 electrons is the same as 10 meters of chain.

You might wonder why I picked 10 m of chain to be equal to a coulomb of charge. Why not 100 m or 1000 m of chain? Because with 10 m of chain, the values of voltage, resistance, and current all fall in the same range as those normally encountered in low voltage electronics.

Note that on most of this Kickstarter page, the spintronic units aren't explicitly used. They're not used here to make things less confusing, but they are used throughout the puzzle book.

Why isn't there a spintronic diode?

It's unnecessary. In Act Two, you learn how to set up a transistor and a junction to act as a diode.

Shipping and taxes are not included in the reward price. Like many other Kickstarters, shipping and VAT/taxes (where applicable) are collected in the pledge manager after the completion of the Kickstarter. (What is a pledge manager?) Since shipping and taxes vary greatly by region, this allows us to be fair to all, allowing us to charge the true cost based on each backer’s specific order and location.

Shipping

To provide the lowest shipping prices and fastest delivery times, Spintronics will ship from the same warehouses that we use to fulfill Turing Tumble orders. Our seven partner warehouses are located in Los Angeles, CA & Chicago, IL (United States Backers), Roosendaal, The Netherlands (European Backers), Blackwood, The United Kingdom (United Kingdom Backers), Melbourne, Australia (Australia, New Zealand and Asia Backers), Toronto, Canada (Canadian Backers), and Fujian, China (Asia Backers).

Shipping prices are estimated for each country in the chart below:

*All pledges with the exception of Gigavolt and the Educator Starter Pack will be sent in one package. For backers of the Gigavolt reward level, Turing Tumble will be sent 2-3 weeks after the completion of the Kickstarter and Spintronics will be sent in Jan. 2022. The Educator Starter Pack will be sent in two separate packages.

Taxes

In compliance with local and country-specific laws, we charge VAT and applicable taxes depending on the state, province, and/or country to which your order is being shipped: