Electronics Explained With Mechanical Devices

Steve showing a circuit built with spintronics blocks

It can be surprisingly hard to find decent analogies when you’re teaching electronics basics. The water flow analogy, for instance, is decent for explaining Ohm’s law, but it breaks down pretty soon thereafter.

Hydraulics aren’t as easy to set up when you want an educational toykit for your child to play with, which leaves them firmly in the thought experiment area. [Steve Mould] shows us a different take – the experimentation kit called Spintronics, which goes the mechanical way, using chains, gears, springs and to simulate the flow of current and the effect of potential differences.

Through different mechanical linkages between gears and internal constructs, you can implement batteries, capacitors, diodes, inductors, resistors, switches, transistors, and the like. The mechanical analogy is surprisingly complete. [Steve] starts by going through the ways those building blocks are turned into mechanical-gear-based elements. He then builds one circuit after another in quick succession, demonstrating just how well it maps to the day-to-day electronic concepts. Some of the examples are oscillators, high-pass filters, and amplifiers. [Steve] even manages to build a full-bridge rectifier!

In the end, he also builds a flip-flop and an XOR gate – just in case you were wondering whether you could theoretically build a computer out of these. Such a mechanical approach makes for a surprisingly complete and endearing analogy when teaching electronics, and an open-source 3D printable take on the concept would be a joy to witness.

Looking for something you could gift to a young aspiring mind? You don’t have to go store-bought – there are some impressive hackers who build educational gadgets, for you to learn from.

16 thoughts on “Electronics Explained With Mechanical Devices

      1. Not OP but I had the same idea, looked up the schematic, realized I’d have to figure out how to make a functional spintronic comparator, pondered the idea of “fighting transitors” where each input is used as a bias voltage for the other and the stronger one wins, then gave up. I’m sure it’s possible (someone already designed a full adder, but it needs so many parts it can only be “built” in an online simulator), but I’m definitely not steampunk-brain enough for the task of making a spintronic 555.

        One step I did look into, though, was a way to have a constant energy source instead of the pull-cord battery… The chains in the sets are exactly the same tooth spacing as chains for Lego gears (in fact they used actual Lego chains in the pre-kickstarter prototypes), but the chains are just a tiny bit too horizontally narrow compared to a Lego gear, so there’s a massive amount of friction if you wanted to drive it with, say, a Technic motor. You could work backward and try to have a Technic motor driving a Lego chain with a Lego gear, that is then attached to a spintronic junction and go from there… but I couldn’t find where my Lego chain links got off to.

        1. Perhaps two transistors fighting might work, if the middle ground was made to float with an inductor or capacitor. Then you’d have some momentum to actuate an output transistor. Perhaps in a latching pair, having the other direction latch another pair, each pair unlatching the other, perhaps by adding capacitance.
          No doubt there’s a less Rube Goldberg way of doing it. Perhaps going back to the bare silicon and looking for an analogy might be a better approach.

        2. I was experimenting with this after seeing the video and messing with the simulator. I was trying to make a basic op-amp so I could try to build some basic analog computing devices. I thought it would be cool to visually see the operation of a basic differentiator or integrator.

          I was trying to do the same sort of dueling transistors layout based on a schematic of a simple op-amp to make my mechanical op-amp (in the simulator)

          I kept hitting issues like the direction of chain motion, the weirdness of the junctions, and just trying to get the 2 transistor outputs to properly combine. After a few hours, I gave up with the idea that I might revisit it when I had more time.

          Writing this comment got me thinking about the issues again and one thing I think I need to explore is using multiple junctions and a resistor to combine the outputs properly.

  1. can someone link to a breakdown of the alleged breakdown of the water analogy? i have seen qualitatively-correct capacitors, resistors, transistors, inductances and even Hall-effect sensors depicted in a water analogy – what is the deficit (apart from the possibly leaky realisation) of such analogies?

    1. I don’t think there is a breakdown, except for electric and magnetic fields (parallel pipes don’t influence each other…). But, that same breakdown exists in the mechanical analog too. I prefer the hydraulic analog personally, but you can flip between a whole lot of domains (heat, pneumatic, can even model financial systems with the hydraulic analogy) It is all just stored energy and rates of change. For a practical high-level understanding the analogies are OK, but obviously they’re not great when considering doping semiconductors or something really low level, which is fine, since at that point I’d expect the person to have a firm grasp of electrical theory.

    2. I think the reason of chains and gears instead of water is, essentially “screw up and water gets everything, well, wet”. Using mineral oils or something similar has it’s downsides if something leaks, too.

    3. It generally breaks down when you get to RF because it’s the fields that are important. There are a pair of Veratasium videos that may help.

      The primary issue is that water in a pipe is contained to the pipe. The pressure and flow only affects the fluid within the pipe and the pipe itself. But EM fields travel through free space and are what carry the energy. A capacitor is one place this difference is important. The classical capacitor does not electrically connect its two leads. Instead, there is a dielectric that electrically insulates the two sides of the capacitor. It’s the electric field across the dielectric that carries the energy.

      An obvious place this shows up is in RF systems. In the Veritassium videos, what he is effectively showing is the impulse response of an antenna and his second video shows a simulation that I think demonstrates this.
      But there are also implications in things like semiconductors where the engineers need to know where the electric fields are for the devices to work as intended.

      Perhaps the most important thing is that the math for the different types of systems diverges. Ohm’s law is useful at a basic level, but once you start trying to apply it to anything other than steady-state DC systems, it tends to break down. Engineers had to invent measures like volt-amps and wrestle with apparent power (and imaginary power) when AC systems were invented. And things go off the rails even more during the invention of radio.
      I think it’s important to remember how long we only had a basic understanding of electricity and then how rapidly that changed.

      These spintronics devices suffer from similar analogy problems but may help people who need a more interactive learning style, have aphantasia, or are just more hands-on type of learners where even the water analogy is still too abstract to be a point of entry.

      1. I think you’re being a little forgetful of when you didn’t know all that you do now about electronics. While the analogy isn’t perfect (nor do the makers of Spintronics claim it to be) it does serve as a gateway to the basic principles of how simple electronic elements interact on a practical level. One need not be aphantasic to struggle initially with any new topic, or to benefit from concrete, manipulable examples. To say only those with no ability to mentally picture hitherto unknown (to them) concepts could benefit is perhaps a little condescending.

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