Tag Archives: math

Evil Mad Scientist Valentines: 2015 edition

Lo Res Valentines valentines

For each of the last two years, we’ve released sets of “Download and Print” cards for Valentine’s day. The 2013 set had six equation-heavy cards, and the 2014 set was a set of six symbol-heavy cards.  This year, we’re releasing six new cards, bringing the collection up to a total of 18 cards. This year’s new cards feature love, hearts, and arrows (but no bows or cupids):

My love for you is real

For when your love is complex, but not whatsoever imaginary.

I love you more every day

For that moment when you want to express that not only is the first derivative of your love positive, but so is the second.

Our love is off the charts

(Just in case there was a danger of none of these being sufficiently cheesy.)

You make me glow

Not sure how we missed this one in last year’s set of symbols.  Alternate caption: “You light up my life.”

Solve for i

And what better way to say “I love you,” than with the gift of a math problem?

2015 Evil Mad Scientist Valentines
Lo Res Valentines

You can download the full set here, which includes all 18 designs from the three years (a 765 kB .PDF document).

As usual, print them out on (or otherwise affix to) card stock, and [some steps omitted] enjoy the resulting lifelong romance.

Play with your food: How to Make Sconic Sections

Sconic Sections

The conic sections are the four classic geometric curves that can occur at the intersection between a cone and a plane: the circleellipseparabola, and hyperbola.

The scone is a classic single-serving quick bread that is often served with breakfast or tea.

And, at the intersection of the two, we present something entirely new, delightfully educational, and remarkably tasty: Sconic Sections.

Sconic Sections: Circle Sconic Sections: Ellipse
Sconic Sections: Parabola Sconic Sections: Hyperbola

In what follows, we’ll show you how to bake cone-shaped scones, to slice them into plane geometric curves, and to highlight those curves by selective application of toppings.  We’ll also discuss some of the methods that didn’t work so well, as we refined our methods for making these.

Onwards, towards parabolic preserves and hyperbolic Nutella!

Continue reading Play with your food: How to Make Sconic Sections

Introduction to Analog Mechanical Computers

Courtesy of the United States Navy comes this incredible introduction to analog mechanical computers.

The context for this is that massive, mechanical computers were used aboard US Navy ships ranging from destroyers to battleships, from about 1944-1969, as part of the “Fire Control” system.  This type of computer would take up to 25 continuously changing input variables in order to calculate the proper bearing and elevation for heavy caliber guns aboard the ship.  This calculation— to ensure that a projectile will land at the place where the target is going to be —is marvelously complex, taking into account variables such as wind speed and direction, relative velocity of the ship and target, and parallax between the different guns on the ship.  What’s truly remarkable is that it was all done with mechanical  mechanisms such as gear differentials, cams, and mechanical integrators.

This two-part training film, from 1953, introduces the basic mechanisms that made these computers work:

The video embedded above (41:53 total length) contains both films, one after the other.  (And, the YouTube link is here.)

Basic Mechanisms in Fire Control Computers, Part 1 discusses shafts, gears, cams, and differentials. Note that the first couple of minutes are not so much about the mechanisms, but more of an explanation— to the servicemen —of why they needed to learn about them.

Basic Mechanisms in Fire Control Computers, Part 2 discusses component solvers, integrators, and multipliers


If you enjoy these training films, you may also want to read through the little book entitled Ordnance Pamphlet 1140: Basic Fire Control Mechanisms, available here in PDF format, which covers much of the same ground.


Pi Blanket


Happy Pi Day, everyone!

To celebrate, our friend Samantha brought in her knitted Pi blanket to share. After the first hexagon with the letter π embroidered on it, the first 127 digits of Pi are shown using the resistor color code to represent the value of the digit. Samantha is donating this quilt to the Project Linus, an organization that gives blankets to children who are seriously ill, traumatized, or otherwise in need.

For those in the San Francisco area, the Exploratorium is celebrating the 25th Anniversary of Pi Day from 1 pm to 3 pm in front of their soon-to-open new location at Pier 15.

Download and Print: Evil Mad Scientist Valentines

EMS Valentines 1

If you’re anything like us, you’ve at some point come across supposedly-nerdy valentines and thought to yourself, “A real geek would have used an equation to express that sentiment.”  And if so, have we have got just the thing for you!

EMS Valentines 3

Here’s our collection of six little valentine cards, each of which adds a little authenticity and class to the not entirely uncommon “geek” valentine genre.

Suppose that you want to communicate to your valentine just how hot you think they are. Sure, you could go with a picture of a thermometer— or a Sriracha bottle —but isn’t the thermodynamic definition of temperature itself in a whole category of its own?

EMS Valentines 5

And what better way to say “I love you,” than with the gift of trigonometric identities?


Lo Res Valentines

You can download the original file here (260 kB .PDF document).

Print it out on (or otherwise affix to) card stock, and [some steps omitted] enjoy the resulting lifelong romance.

Update: The 2014 and 2015 valentines have been released!

Digi-Comp II: First Edition


We’re pleased to finally announce availability of our brand new, long-awaited kit, the Digi-Comp II: First Edition. It’s a modern, fully-operational recreation of the original Digi-Comp II— the classic 1960′s educational computer kit —CNC routed from hardwood plywood.

The Digi-Comp II is a binary digital mechanical computer, capable of conducting basic operations like adding, multiplying, subtracting, dividing, counting, and so forth.  These operations are all conducted by the action of balls rolling down a slope, directed by mechanical switches and flip flops, and all powered by gravity.

We’ve been working on project for over two years now, and so we’ve written before, in some detail, about how the Digi-Comp II works, and what kinds of things you can do with it. We’ve written about our larger than life version of the Digi-Comp II, which uses 8 Balls.  We showed off that version at the 2011 and 2012 Bay Area Maker Faires and made a demonstration video to show how it works.   We have also written about our smaller wooden prototypes that we displayed at the 2011 Maker Faire New York.



Our new version, the “First Edition,” is a descendent of the latter.  As compared to the “2011” model, it has a huge number of refinements— including an improved ball feeder that both fits 30 balls at a time (so you don’t need to refill during most calculations) and is jam resistant, a more compact and reliable start lever, better labeling, better flip-flop design, and internal baffles that slow the balls down, to prevent them from flying out of the machine.



Many of these improvements were made possible by slightly reducing the size of the balls that we use.  Whereas the “2011” model used ½” ball bearings, the First Edition uses standard 11 mm pachinko balls, which are easily available, shiny, and rust resistant.  The fact that they are slightly smaller has allowed us to shrink some of the main circuitry, to allow for that larger ball feeder, to use thinner flip flops, and to fit the full machine into the same 10×24″ envelope that we had aimed for, which is considerably more compact than the 14×28.5″ size of the original.



One of the nice things about keeping the size under 24 inches long is that we can fit the entire top deck of the Digi-Comp II into our 12×24″ laser engraver— so that we can directly laser engrave markings onto the playfield.  And while it’s nice to be able to write out DIGI-COMP II in huge letters, the more important application is actually adding the individual markings by the flip-flops and registers:


You may notice that the laser marks are very sharp on the “mesas” of the playfield, and less sharp but more bold down below.   This is an intentional effect, created by laser engraving the playfield in a single pass, with the laser focussed just below the level of the “mesas.”  On previous versions, we’ve either lasered the two parts independently, fully in focus at each depth, or focussed the laser halfway between the top and bottom— which leaves the engraving to look uniform, but less sharp, at each depth.   But this method seems to create exactly what we want:  sharp up top where it’s easier to read, and bold down below where it’s harder to see.



The playfield itself is made of 1/2″ thick maple-faced veneer-core all-hardwood plywood.  This is a rock-solid material that is about as far from “hardware store” plywood as you can imagine.  We use a CNC router to cut the pivot and limit holes for the flip flops and to carve the channels— roughly 3/8″ deep —where the balls can roll.  The CNC router is precise enough that when we cut the channels for the balls, we evenly split one of the veneer layers, ending up with a clean inner surface.  The Digi-Comp II also has a lower deck, below the playfield, that supports the clear-register and complement functions.  The lower deck is carved in the same way, but does not have any laser engraving.



The lower deck is attached below the upper deck by six screws that come down from the top to meet six wing nuts below.  Between the two layers are 3/16″ spacers that keep the decks uniformly separated.  It turns out that it’s actually important to use six screws; our earlier prototypes tended to jam up when the spacing between the two layers wasn’t controlled well enough.

One of the other improvements is that the “First Edition” kit has a very sturdy stand, as shown above.  The laser-cut stand on the “2011” model was flimsy, and the simple dowels on the original 1960’s kit were not much better.   The new stand is a glued assembly made of two rigid legs and a crossbeam, made of the same remarkably-hard plywood as the rest of the machine.  It can be attached to or detached from the playfield with the two fat thumbscrews.  It holds the playfield at an even 30° from horizontal, such that the top sits about 12 ½ inches above your desk top— a particularly good angle for viewing the playfield.  The stand is actually reversible, so that you turn it the other way and raise the playfield only about 20° from horizontal, giving the option of a slower speed of operation.  If you want to go faster instead, you can overclock the Digi-Comp II by putting a book below the stand to increase the angle.


The new ball release mechanism has been fine-tuned and greatly simplified.  We recently showed off a little video demonstrating how this part of the machine works.  The start lever— now nicely labeled —is made of laser-cut poplar, has a brass rivet as its bearing and a glued-in pachinko ball as a counterweight.  When pulled down by a human or a rolling ball, it pushes a stainless steel rod that moves the ball release at the top of the machine to release the next ball.



Finally, it’s worth noting that this is called the “Digi-Comp II: First Edition” for a reason: We are planning others.

The original 1960’s Digi-Comp II kit was made of thin vacuum-formed plastic (what we more often refer to as “coffee drink lid material”), supported by a sheet of masonite and fitted with injection-molded flip-flops and switches.  Our CNC-cut wooden versions are much more substantial, but also cost a lot more to make, both in terms of raw materials and fabrication time.  We’ve been slowly working towards what we hope will be a happy medium: a Digi-Comp II made of (more substantial) vacuum-formed plastic, reasonably sturdy, and at a more modest cost.  We still plan to release a version like that, hopefully within the next year.  This has been a long journey for us— making wonderful machines mostly because they are wonderful machines —and we’re very happy to release our first one into the world.


The Digi-Comp II: First Edition is now available to order at the Evil Mad Scientist Shop.

Evil Mad Scientist Laboratories: Year 4

Pi Pie Trivet

Pi (squared) trivet - 9

Happy Pi Day! Pi day was just made official. In honor of National Pi Day, we present a pi trivet, perfect for cooling your Apple pie (or pi pie) on.

Pi (squared) trivet - 6

Besides just the letter pi, The number pi up to the first thousand digits after the decimal are laser engraved into half-inch thick cork. The overall size of the trivet is about seven inches, square.

Pi (squared) trivet - 2

This cork is actually gasket material from McMaster-Carr, which has a wonderfully smooth and even surface. Compared to many of the other cork materials that we have seen– like that used for many cheap trivets– this has very little pitting and the surface shows fine detail very well.