Mini-Me

A few years ago I thought I had hit the pinnacle of my career as a writer when a kid came up to me just before a book tour talk and showed me a picture of his cat, which he had named Theo after me. What could possibly top that?

Well, I just found out! Behold, here is Liam, a third-grader, dressed up as me, complete with painted on beard! For a school project he was supposed top pick a favorite author, write a biography, and dress up as his chosen person. He chose me! How cool is that! Sadly two important details of his portrayal are now out of date: I don't have a beard anymore (new girlfriend) and I don't have any hair on top either (old age?).

Thank you Liam for making my day.

I Made a Clock!

I made a clock today and I'm so happy it actually works! It runs upwards of 20 minutes before you have to rewind it, and is currently running at about 58 seconds per minute. Baby steps, ok, baby steps.

The image above is the CAD file showing the frame (back and front), gear train, dial faces, and the all-important escapement (on the left).  We haven't done any proper photography of it yet, but watch this video to see how it works, fastened to a shelf in my laser cutting bunker:

As you can see, this is a very spread-out clock. The gear chain is laid out in a line: second-hand on the left, minute-hand in the middle, and hour-hand on the right, with each hand having its own dial face. I did that so you can see the gear chain that reduces the speed by factors of 60 and 12 respectively between the second, minute, and hour hands. Analog clocks with hands, even ones that run on a battery, are all about this gear chain. In a normal clock they fold it in on itself so that all three hands end up in the same place, on a single dial face. That's great for being a useful, compact clock, but terrible for seeing how the gears work. 

A crucial part of every purely mechanical clock is the escapement. This is the part of the clock that translates the swinging motion of the pendulum into rotation at a precisely measured rate, and at the same time imparts tiny bits of energy to the pendulum on each tick, in order to keep it swinging.

There have been many designs of escapement over the 700-odd years since the first "verge" escapements were developed in the late 1200s. My clock uses a version of the "anchor" escapement, the second type to come into common use (in 1657). There are newer, better designs, but they are less tolerant of mechanical imprecision. Clocks, and escapements in particular, are dependent on very high precision machining, so much so that it's fair to say that the entire field of precision metal working advanced for several centuries mainly to make better clocks. While I love my laser cutter and consider it to be a very precise tool, by the standards of clock making it is horribly crude. Good clock parts have errors measured in thousandths or ten-thousandths of a millimeter, so my laser cutter's tenth of a millimeter precision is pretty bad. 

But, it's good enough to make this fully functional escapement, and that's what matters to me. (These, by the way, are the escapements that didn't work.) It took about a dozen tries before I got the dimensions just right so it would reliably advance, and also send enough energy to the pendulum. 

Another crucial thing about a good clock is how friction-free it is made. The less friction, the longer it can run before it needs to be rewound (either by re-coiling a main spring, or by lifting up weights whose slow dropping provides energy). To achieve low friction, all kinds of tricks are used, including extra-fancy oil and even "jewel" bearings made, typically, of sapphire. I have one "anniversary" clock that runs for an entire year without being rewound!

By contrast, my laser cut acrylic clock runs for about 20 minutes before the weight (shown here) hits the floor. The weight is a hollow acrylic octagon, and if I make this available as a kit I will suggest that people fill it with whatever heavy things they have handy, like pennies for example. I filled it with #6 hex nuts, because I have a lot of them. The weight falls fairly fast because it's connected at a point in the gear chain fairly close to the escapement, where the gears are turning relatively fast. If I connect it later on, where it would turn much more slowly and thus last much longer, there is too much friction and too much gear reduction, causing too little energy to reach the pendulum, causing the clock to stop.

The pendulum bob, shown here, is the same design as the weight. Here's an interesting fact I learned in trying to decide how long the pendulum needed to be for it to tick at the correct rate. (The period of a pendulum is directly proportional to its length.) It turns out that a pendulum with a period of two seconds (which will tick once every second, since the escapement advances once every half-cycle of the pendulum) has a length very close to one meter. Why? Because that was the original idea for how a meter should be defined: one meter was proposed to be the length of a pendulum with a half-period of one second.

This did not end up being used as the definition, at least not officially. Instead they went with "a meter is 1/10,000,000 of the distance from the earth's equator to the pole", which is a completely ridiculous basis for a unit of length. It's always bothered me how utterly arbitrary and useless this definition is, especially since that distance was not actually known with any great precision at the time. It's always sounded to me like a post-hoc justification for a length they'd already settled on for some other reason. (Like, for example, that it's about the same length as the English Yard, but that couldn't be it because the French hate the English.)

Now it all makes sense: it was a post-hoc justification. The length of a one-second pendulum is a much better basis for a unit. It's something that could be reproduced by anyone, anywhere who is able to determine time accurately (which you can do from the sun, for example). But no, they went with the silly equator-to-pole distance. I'm assuming politics was involved. (Since no one could actually use the equator-to-pole distance, they had to make a "prototype" meter, a platinum-iridium bar kept in Paris for many years until the definition was updated to be in terms of wavelengths of a certain frequency of light, and then later in terms of the distance traveled by light in a specified time.)

Well anyway, at this point I have one copy of this clock, and I'm going to make a second one that will put together with gloves on, in order to photograph it for my book. I might also make it into a kit for sale at mechanicalgifs.com, if it seems like something people would like. Comment if you want to lobby for it being available....

I Made a New Engine!

I'm was at the G4G conference last week and working on my (6-minute) talk caused me to think again about the motivation behind making steam engine models. 

Nearly all model steam engines (and some full-size ones) use a beautiful set of harmonic motions to create the self-sustaining, alternating application of steam pressure to first one side and then the other of a piston, which drives a flywheel, which in turn drives a valve that causes the alternating steam pressure.

This model shows the fundamental fact that the two harmonic motions, that of the piston and that of the valve, are 90 degrees out of phase. When the piston comes to rest, the valve is moving fastest to switch the steam over to the other side.

This is a beautifully simple mechanism, and it's the smoothest possible way of running an engine: everything is in harmonic motion, meaning the least possible change in acceleration at every point in the cycle.

But, it requires two connection points to the flywheel, which seems like something that could be subject to further simplification. If you could make a mechanical differentiator to take the derivative of the sine wave motion of the piston, you could use that to synthesize the cosine motion of the valve. But that's not possible in any pure way, because you would necessarily require infinite leverage or something to that effect. (Because the valve needs to be moving at maximum speed when the piston is stationary: how do you derive motion from lack of motion?)

But it turns out there is a simple and commonly-used (on real steam engines and some models) way to achieve a sort of approximation to the cosine wave. And the curve you get is actually better than a cosine, in that it makes the valve move faster exactly when needed, and remain completely stationary when it doesn't need to move. The motion is not smooth, but it serves the engine better. Notice that this design has only one takeoff, yet the motion of the valve is still maximized at the point where the piston comes to rest (actually just before).

The trick is to use the very top/bottom of the sine wave, magnify it (with mechanical leverage), and then min/max it (with a sliding toggle) to create hysteresis. Mathematically, the motion of the toggle is approximately 5 * max(0, sin(x) - 0.8), with appropriate switching of the sign for the negative lobe of the sine wave. This plot shows the piston (green) and valve (orange) positions as a function of time through one complete cycle.

If you add a cosine wave to the plot (actually -cos(x)), you can see how the jerky, toggle-based curve is a mechanical approximation of a cosine, but squared off. What you actually want from the point of view of steam flow, is a square wave: the valve should switch instantly from one side to the other, exactly at the extremes of motion of the piston.

The whole elegance of having two pure harmonic motions is really not ideal at all from this point of view, which is why such mechanisms are not used on large engines.

There is another "mathematical" way of looking at the difference between engines that have separate sine and cosine connections to the flywheel, vs. a single sine wave connection. The combination of a sine and cosine wave define a direction of time, as it were. With time (x-axis) moving forwards to the right, the sine wave leads the cosine wave. If you reverse time, the cosine leads the sine. Therefore, this engine can only run in one direction (unless you interchange where the steam is coming in with the exhaust).

But a single sine wave does not change if you reverse time: it is symmetrical to time reversal, as they say in physics. That means, necessarily, that the single-connection engine above must be able to run in either direction without changing anything in the mechanism. Another way of looking at it is to say that the entire mechanism to the right of the flywheel has no way of knowing which direction the flywheel is turning. The harmonic, sine wave motion will be identical regardless of the direction of rotation, therefore it must work either way. So what determines which direction it actually goes? It's all down to which side the valve was flipped to when the engine is started up. The hysteresis of the valve creates the direction-of-time difference.

That's actually a thing in real engines: I saw a model steam engine with this type of valve just a few days before making this design. The guy showed me how you flip a lever before starting the engine, and it was clear that this lever was not redirecting steam. At the time I didn't understand how this could work, which caused me to worry about it until I finished this model, and now it all makes sense.

Literally hundreds of patents were issued over a span of centuries, focused on improved methods of controlling the timing of steam engine valves. For example, you might want to optimize for maximum work per unit of water used to create steam, instead of optimizing for maximum power from a given size of piston,. If so, you design the valves to admit a small amount of high-pressure steam at the start of the cycle, then close off quickly, allowing the steam to expand within the cylinder. The pressure drops off as the cylinder moves over, but you don't use any more steam. In practice this is said to get you about 2/3 of the work for 1/3 of the water, compared to applying full steam pressure for the whole stroke.

Towards the end, before the steam engine was replaced completely by internal combustion and turbine engines, the valves were mostly "poppet" style valves, driven by cams. The timing could be changed at will to optimize for torque or efficiency.

Theodore

P.S. I love my laser cutter! As I said, I came up with this design while working on a talk. That was Monday evening, and my flight out to the conference was Wednesday early morning. Around 11PM that night I decided it was nuts to try to actually make the engine in time to take to the conference, so I started working on the CAD files. By around 1AM Tuesday morning I had a design ready (based on my Folded Steam Engine, lengthened a bit and with the valve connection replaced with the new design). Around 10AM Tuesday morning I went to the shop and laser cut the new design. It took four or five re-cuttings of the piston and toggle lever to fine-tune the dimensions so the valve moves the correct distance (taking into account the reality of the laser cut width and the slop in the screw pivot joint, which are a bit hard to predict in the drawing).

Once the design was good, I made six copies, put a couple of them together, then Nick and I photographed a time lapse of the new design. All that took maybe 2-3 hours.

I really do not know of any tool that works so fast and so perfectly to churn out beautiful-looking mechanical parts. I really wish 3D printers could come anywhere near this level of speed, economy, and beauty of results. While waiting for that, I will continue to live in my 2D laser cutter world.

Mechanical GIFs Models Now Available Open Source on Thingiverse

I've finally gotten around to my original intention of publishing the plans (layered DXF files) for all the laser-cut acrylic parts of all the models featured at mechanicalgifs.com.

You can find them at my Thingiverse collection. I have no idea if anyone will actually try to make them from the plans. I'm pretty sure that, unless you already have all the different parts and types of acrylic on hand, it would be cheaper to buy my kit of the same thing. But on the other hand, it might be more fun to make your own parts? If you're the sort of person who would make this sort of thing from Thingiverse plans, I'd be interested in opinions.

I call it the Bagger 2000

I promise that some day I will write about something other than making kits, but for now that's what I'm all about. Today I'm pleased as punch about my new semi-automatic small parts bagging tool, which I call the Bagger 2000 (because it holds and fills 20 bags at a time, and because 2000 is a hundred times better than 20 as a model number).

The issue is this: we need to fill hundreds of 2" x 4" poly bags with lots of little nuts, bolts, and small plastic parts. Each bag gets a dozen or more different parts, and sometimes a dozen or more of one particular part.

We had been doing this using a batch of 20 pill counters (small trays with a trough on the side, designed for counting out pills in a pharmacy). This works, but it is tedious, and the sides of the trays are very low, meaning there is a constant danger of a part getting knocked out before it's emptied into the bag.

What I wanted was some kind of system where I could drop parts directly into the bags using a funnel, or something like that. But it would have to be 20 funnels, one for each bag in the batch, and I couldn't think of a good idea for how to hold the bag onto the end of the funnel, how to hold up the funnels, and so on. Until I realized that I own a laser cutter and have been practicing my inventing skills.

Here is the result: the Bagger 2000!

Being made entirely of clear acrylic, this object is actually quite difficult to decipher from a photo, so here's a short video that gives a better idea of its three-dimensional structure. There are 20 individual rectangular funnels: at the bottom of each, the acrylic sides have been bent around to form little upwards-pointing hooks.

To use the device, you flip it upside down and load it with 20 poly bags. The acrylic clips grip the zip closure on the poly bags. Flip it back right-side-up and you have twenty bags hanging underneath 20 funnels.

You can drop items directly into the bags. Here I've added the screwdriver and wrench included with most of the kits:

But dropping things straight into the bag is not ideal, because (a) it's very hard to recover if you accidentally drop in too many, and (b) it's hard to double-check that you got the right number, for items where there are multiples. (E.g., did I just drop in 3 or 4 of those tiny screws?)

What's needed is a staging area where items can be laid out in plain sight, before being dropped down into the bag. My big breakthrough on this project was realizing that the semi-automatic parts counter (described in an earlier blog post) was perfect for this job. The funnel array has exactly the same dimensions and spacing as the parts dropper, so when the dropper is placed on top of the funnels, they line up perfectly.

Here is a video showing how an assortment of different lengths of screws (manually counted and placed on the parts dropper) can be inspected before being dropped:

Here's a side view showing how the parts are guided down into the bag.

Basically this is the exact equivalent of a German "inspection toilet", which includes a special staging area to hold your you-know-what before it gets flushed down to the big poly bag at the end of the pipe. (They do this because they think it's important to inspect your you-know-what for any signs of health or diet problems every single time. Yes, this is for real, though becoming less popular over time, as I understand it.)

Where the Bagger 2000 really shines is when it's combined with the parts counting feature of the parts dropper. Here the parts counter, positioned on top of the Bagger, is being loaded with 16 hex nuts for each bag. You just wipe a pile of nuts over the counting plate.

Then, after double-checking that all the holes in the template are filled, you simply pull back the gate and presto-magic, all the nuts are dropped perfectly into their respective bags. 320 nuts (16 times 20) counted and put in bags in about a minute!

When the bags are finished, you just pick them like ripe fruit from the underside of the Bagger:

This machine has at least doubled the speed of filling the average kit bag, and I think it will also contribute to a lower error rate.

I'm just about ready to start wondering how other people solve similar problems. My approach to learning about a new area is often to try to do it myself first, without looking too closely at how other people do it. Then, when I feel like I have a really good handle on what the issues are and where the difficult problems are to be found (i.e. what have I not been able to figure out myself), then I'll do some research. Usually I find out that there are much better solutions, but I feel it's worth doing the messing-around phase first, because that's the only way I can properly appreciate how clever the better solutions are.

Production Update: Making a hundred of something

I'm at the stage now of needing to make about a hundred copies of several of my mechanical gifs kits. There's a balance between spending time making the kits, and spending time making tools to make the making of kits faster. How much automation is right depends on the scale of operation.

We have settled on a system of making 20 copies of each kit at a time, mainly because that's how much table space we've got readily available. (This shows 20 Combination Lock kits nearly ready to be placed in their retail boxes.)

A couple days ago my photographer Nick suggested a simple device to semi-automate one of the problem steps: counting out a dozen or so small items. (For example, twelve #6 hex nuts for each Combination Lock kit, or 42 nuts for the nightmare Transaxle kit.) After some prototypes and design improvements, I've ended up with a device that lets me count and place twenty copies of a given number of items, quite efficiently, and with hopefully a very low error rate.

 

The first step is setting up 20 pill counting trays and adding the small parts (nuts, bolts, etc, anything that will fit in a 2" x 4" plastic bag). They are always laid out in a 4 x 5 grid, for consistency.

 

 

The parts counter is also arranged in a 4x5 grid, so it not only counts each individual group of parts, it also confirms that all 20 trays have gotten their dose of parts. A custom template slid in the top determines how many of what shape of object will be counted out. Here it's seen loaded with six springs in each of the 20 positions, for the Pin-Tumbler Lock kit.

Below we see it in action counting out seven #2 nuts, also for the Pin-Tumbler Lock kit. This is literally Koatie's first time using the new device: we both got much faster at it after a few passes!

Nuts are particularly well-suited for this kind of device, because they fall automatically into the holes in the template. We can fill it just by wiping a bunch of nuts over the top and then pouring off the excess. But the template seems to work well even for things that have to be placed one-by-one into the slots. For example, these pins for the Pin-Tumbler Lock don't fall into place, but it still faster and more reliable to manually place them into the slots, and then dump them out automatically.

If you're curious, here's the first step in the second stage of the assembly process: the larger acrylic pieces. Those are laid out on squares of bubble wrap, after being laser-cut. Here's a 32" x 48" sheet of about half the parts for 68 copies of the Pin-Tumbler Lock:

Well, I hope you're not bored with my endless details about manufacturing. It's a learning process, that's for sure.

Now Available, a New Dimension in MechanicalGIFs: The Third

Today I am officially announcing a new set of six fully three-dimensional, transparently obvious acrylic models, all available at mechanicalgifs.com. As before, they are highly simplified and stylized models of mechanical devices (just not quite as simplified as the earlier, flatter ones I've had available since late last year).

I think my favorite of the new batch is the combination lock, which goes nicely with the older pin-tumbler lock model. The little gif here only shows it from the front, but watch the video below and you'll see that it's a complete, 3D mechanism. The three "tumblers" have notches and pins whose relative locations determine the combination that, when entered, will cause all the notches to line up directly underneath the "fence", allowing it to fall into place and open the lock.

(This is a model of a fancy style of safe lock, which uses a clever cam mechanism to allow the code dial to also act to withdraw the bolt, opening the lock.)

There was a gif posted recently on the mechanical_gifs subreddit (link to Reddit post) which illustrates basically the same thing. It's neat, and got to the front page of Reddit with tens of thousands of upvotes. But I think mine is better....both because it's transparent, so you can see the pins that link the tumblers together (which are not visible in the Reddit gif), and because it's a real physical objects you can hold in your hand

That's the whole point of this exercise. These models combine the explanatory power of a simplified, schematic animation with the visceral, hands-on learning only possible with a physical object. 

I've really tried to make these models as affordable as possible by designing an efficient production system and setting the price as low as I can (consistent with not losing money once they sell in reasonable volume).

They could be cheaper if they were being sold in very large quantities and were made in China from injection-molded polystyrene (and maybe some day they will be). But for now they are made in Illinois from precision laser-cut acrylic, which is just a lot nicer, and a lot more realistic for getting started. It would costs many tens of thousands of dollars to get them into production with molded parts, but we can make them 20 at a time here for what I think is a pretty reasonable price. The only startup cost (not counting cost-of-goods-sold like acrylic, nuts and bolts, etc) was the large laser cutter and a whole, whole lot of storage bins to hold the different parts. (The Combination Lock alone, for example, has 117 parts of 51 different types!)

The pinnacle of industrial development for any country, historically, was reaching the point where they were able to manufacture entire cars. (Recently the bar has been raised to being able to launch those cars into space.) So I decided that I too should be able to manufacture an entire car. Thus was born the mechanical gif Radial Engine Car model.

It's a lot more expensive than any of the other models (it incorporates four other models into a single unit, and adds additional chassis parts). But, if I do say so myself, it's seriously cool.

Nick insisted on shooting a drone video of the car in action (though we were actually just holding the drone up by hand since the fool thing is only a foot long and goes about two miles per hour):

Yes, we used a drone, but only because Nick insisted. We didn't actually turn it on. (Not as stupid as it sounds: a drone like this is an excellent steady-cam, because its gimbal mechanism remains active even when the propellers are off.)

The car looks kind of goofy with its hugely-out-of-proportion mechanical parts—and literally no driver's seat. Why? Because who cares about people, this is about machines. The parts are sized in proportion to their mechanical significance, just as the hands (and lips?) of this "cortical homunculus" are sized in proportion to how much brain power is dedicated to each part.

Both are distorted to show what matters, while minimizing the decoration and dead weight that dominates the practical, real-world versions.

Well, I hope y'all appreciate the effort that went into designing (and actually making!) these kits, and that you'll consider getting one for yourself or that mechanically curious kid you know (12 or older for legal reasons).

But you know what I'd really like? For someone to post a few of them to the mechanical_gifs subreddit.... Every time I try to post something on Reddit it gets buried, but maybe one of you will have better luck? I think they are super-relevant to that particular subreddit. In fact, they are so relevant that the fixed sidebar at r/mechanical_gifs actually contains a gif animation of a steam engine that is almost identical in design to my Two-Eccentrics Steam Engine. Which is surprising since (a) I didn't know that before I designed mine, and (b) I didn't think any real steam engine would actually be designed that way. But there is it, just waiting for someone who isn't me to point out that it's available in physical form right now.

V2 Mechanical Gif Car

I like this stage of a project.

It's the point where something that seemed like crazy pipe dream is sitting on the kitchen table.

Over the past few months I've designed four separate mechanisms: a radial engine (currently for sale at mechanicalgifs.com), a transmission, a differential, and a steering mechanism. Each of these is a nice, self-contained model of similar complexity to all the models I currently sell. 

But then I thought it would be cool to put them all together into...drum roll...a whole car. I spent several weeks thinking this was a dumb idea. It was just beyond my present capacity for designing 3-dimensional models, and surely it wouldn't really work, and I can't be wasting that kind of time right now. But....if I could do it...wouldn't that be so cool?

About a week ago I posted about the first draft of this idea, which combined engine, steering, and differential in a rather clunky and inelegant way. Now I've finished V2 of what is turning into a most pleasing device. I re-designed my transmission model to make it fit into the scale and shape of the car (and to work around various logistical issues that come about when you try to link together multiple mechanical stages without using any universal joints or shaft passers)

Here's a video overview of the car in action:

The differential and steering are the same as before. You can see more videos of them in my earlier blog post, but here's a new angle on the rack-and-pinion steering mechanism. (The tires, by the way, are red Tygon micro fuel line slit down its length. I'm not sure I like them, but they do give the wheels at least a bit of traction.)

I'm particularly pleased with the transmission. (OK, the current version is a bit sticky, but I know why and I can easily fix it in the next iteration.) Here is a top view showing how it shifts from low gear to neutral to high gear, and then back down again.

And here is a view from the back, through the differential. I like the pale blue acrylic used for the big gears, because it's dark enough to really stand out when viewing the gear on edge, but from the side you can see very clearly through it.

I did my best to use colors and shapes to expose and bring clarity to the dual-clutch mechanism that lies at the heart of this kind of transmission. Notice that all the gears are always fully engaged with each other and in constant motion: when you shift badly and "grind the gears" you are not actually grinding any gears. 

Instead the shifting is accomplished by moving a clutch plate that locks alternately one or the other output gear to the output shaft. The lower gears spin freely on the output shaft: only the center spinning disk is on a square shaft that rotationally locks it to the output shaft.

When shifted all the way to the left or right, green teeth on the central disk engage with pink teeth on the output gears to lock one or the other of those gears to the output shaft. The "grinding" is grinding of these clutch plate teeth: it happens when they are not spinning at close to the same speed when they are pushed into each other. 

(This is a two-speed transmission for simplicity. In 3, 4, or 5-speed transmissions they simply have more gears of different sizes, and more clutch plates. Reverse gear is done with an extra gear off to the side that reverses the direction of rotation before transferring the motion to the output gears.)

You can sort of "drive" the car across a table, either by turning the engine:

Or by pushing it along, driving the engine from the wheels. (You can do this with a real manual-transmission car too: it's one way of starting a stalled car with a dead battery, but only works if you have a hill or a bunch of people to push, and some luck.)

Aside from the addition of a transmission, the biggest difference between this version and the previous one is that, instead of an awkward plate across the whole top of the car, I've got a pair of side rails, which even shift into different planes on both sides of the transmission to account for the different widths of the differential vs. the steering block. This took a long time to figure out, but of course it's nothing compared to the complexity of designing a real car—let alone something insanely complicated like an airplane.

I remember reading that there was a team of a dozen engineers who worked for several years on the design of one door for a new passenger jet. This is complicated stuff. And while we all marvel at the software on a modern iPhone, take one apart and the mechanical complexity alone will make you question whether's it's even realistic to think that human beings designed it.

But the way these seemingly impossible things are done is always the same—in layers. You break down the task into smaller and smaller units, define interfaces between them, and then work out the details one step at a time. To build this car, I first had to design an engine, a steering mechanism, a transmission, and a differential. Each of those is a problem that can be solved on its own. (And each contains sub-problems, like designing a gear, or a square frame to hold four gears, etc.)

When it comes time to integrate the separate sub-systems, there is the exciting possibility of merging and integrating parts that were designed separately. This meta level of design is often the way in which more refined, evolved products differ from first-generation models (in the real world as well as in my world of pretend cars).

For example, the first generation of my differential and transmission each had two "bearings" (holes in acrylic plates) that the drive shaft went through. That's necessary, because without two bearing, the shaft won't stay where it belongs. So the first version of the car (on the left) had a total of four walls supporting what had become a single drive shaft running from the transmission to the differential. This is not only overkill, it also made for a very sticky shaft.

An intermediate stage (not shown) had only three bearing points, and for the final version I realized that I could actually get it back down to just two bearings by completely blending the transmission and differential (right view):

I have a suspicion that is is basically what's called a transaxle, used in front wheel drive cars, but I don't actually know much about automotive engineering so I'm just guessing here. EDIT: I have since been informed that this is in fact exactly a transaxle, and it's used in both front and real wheel drive cars. The Wikipedia article on transaxles has a nice picture of one that looks exactly like mine, except made of metal and more complicated.. You can see the same gears, clutch plates, fork for pushing the clutch plate, and differential housing. (At least I assume it's a differential housing, and the article claims it is, though it looks rather small to me.) Here is a cutaway drawing of a transaxle also pretty much just like mine.

Another real-world example of this sort of integration is in the transition from chassis-based cars to unibody cars. The first cars all had a strong steel frame, or chassis, that the mechanical components were fastened to. When the whole chassis is finished with the guts connected, then the body panels are bolted on as a sort of decoration. (Trucks and serious off-road cars are still built this way.)

In a unibody car there is no separate chassis, and instead the mechanical components are integrated and supported by the body itself. This is much harder to design, but it allows for greater flexibility in the shape of the car, makes it lighter, and cheaper.

It's fun re-living these stages of the industrial revolution, and the mechanical evolution of the modern world, in miniature form sitting next to my magical laser cutter.

Beginnings of a Whole Car

As reported in earlier blog posts, I've recently started selling "Mechanical Gifs", highly stylized acrylic models of simple mechanisms designed to illustrate how the things work—the same way an animated gif would, but in physical form.

The models currently for sale are one mechanism at a time: A lock, an engine, etc. But I've got a lot of other designs in my back pocket waiting to come to life (and to the store). Here is a preview of the inspiration I had a few days ago to combine several models I have been working on into a complete working car. (Well, more like the skeleton of the most fundamental working parts of an imaginary radial-engine car.)

Here's what it looks like if you push it across a table. The mechanism is smooth enough that the whole drivetrain turns even though there is almost no friction between the smooth acrylic tires and the smooth varnished table top.

Here is a video showing how the radial engine (a slightly modified copy of the one for sale at mechanicalgifs.com) connects to the differential (an unfinished design not currently available). Yes, there is no transmission and no universal/CV joints. Simplicity is key here! This is essence of car, not reality of car.

Here is more of how the differential works. (I didn't have anyone to hold my phone, so I can' show you how it works when the driveshaft is turning and you hold one wheel. Which is the whole point of a differential.)

Here's a close-up of the rack-and-pinion steering mechanism in action (top and bottom views):

The differential and steering mechanisms are not final designs, but neither are they first-generation. Both of them have been through 4 or 5 cycles of design, laser-cut, build, improve. For example, notice the little wings on the sides of the green rack gear in the steering mechanism? They extend as far as the ends of the joints connecting the rack to the tie rods. Without those wings, the rack tries to twist out of parallel when it's turned all the way to one side or another. Of course I didn't realize it would do that before I built one without wings.

I have several ideas already how to improve this design. For example, I'm going to replace the flat table-top connecting all the parts with two vertical rails running down the sides of the model. This will save plastic and make the whole thing much stronger and stiffer.

I'm also pretty sure I'm going to add a 2-speed transmission before finalizing the kit. (I have a design for a transmission, and it sort of works, but it's definitely not ready for prime time yet.) I don't think I will add any kind of suspension or universal joints: these parts do not feel to me as fundamental as the engine, transmission, differential, and steering.

My goal in all of these mechanical gifs is to simplify down to the most essential aspects of the design, to focus attention on the principal motions. In this case I wanted to find the essence of an old-school internal combustion car (electric cars are a whole other can of worms).

Of course you can't have a car without an engine, so that's definitely in. Without a steering mechanism you can only go in a straight line, so that also seems pretty fundamental. And if you have only one engine, then you must have a differential, or you will tear up the tires and axles as soon as you try to go around a corner. 

The transmission you could live without, but all real cars have one, because internal combustion engines are only efficient in a fairly narrow range of rotational speed. You have to have gears to let the speed of the wheels vary over a wide range, while keeping the speed of the engine in a narrow range. (Electric motors don't have this problem, and they are small, so you can just put a separate motor on each wheel and get rid of both the transmission and the differential.)

The other nice thing about a transmission will be that it shifts the axis of the drive train, so I can move the axis upwards, allowing the engine to be in a more natural , higher position while the differential remains lower down.

Stay tuned, maybe in a week or two I'll have the transmission installed.... (Sorry, not much chance of this being for sale before x-mas.)

P.S. Brakes? We don't need no stinking brakes. Onward!