The Stepped Drum Mechanism. 12 Days of Curtsmas 3

12 Days of Curtsmas Chapter 3: The Stepped Drum Mechanism
The basic arithmetic in the Curta is performed by the Stepped Drum, also called the Leibniz Wheel or Leibniz Drum.
This is a Curta Type I, built in 1952. Stay tuned for episodes every other day, December 3 - 25. Thanks as always to the person who gave me the Curta.
Chapter 11 (December 23) will be a mailbag episode! So please ask questions, etc.
End song inspired by "Hotter than a Molotov" by The Coup. • The Coup: Hotter Than ...
Jingle bells sound from www.freesoundsl..., CC-BY-4.0
Curta parts 3D-model from www.thingivers...
CC-BY
Stephen Freeborn's Archimedes F Junior video
• Archimedes F "Junior" ...
Robert Baruch Monroe model K video
• Disassembling a 1920s ...

[@getjaketospace]

I hope day 12 is just 10 minutes of Curta pictures being layered on top of each other

[@chriswalford4161]

That’s almost pornographic

[@chriswalford4161]

Parallel universes, huh? So it IS a quantum device. Knew it!

[@randomcuber230]

?

[@stephenfreeborn]

Thank Chris. It’s so odd to hear your own name on someone else’s video. Now the pressure’s on to say more good things.

[@ChrisStaecker]

everybody should click on this gentleman

[@zaquery8]

Who knew popping the doink could be so illuminating!

[@ColtonRMagby]

That mechanism is simple, yet very effective. That's genius.

[@thatskyfox]

This is so satisfying to watch. Clever design, clear explanation and best voice commentary XD

[@ElectroNeutrino]

Don't forget to pop the doink.

[@jwrm22]

After the 2nd day, I'd expect there wouldn't be much to talk about. Making me quite a bit more excited for the 12th video :)

[@Ravlen1]

Thanks a lot Chris, this is exactly the kind of thing I was wondering about when you asked if we had any questions (I wanted to learn about which mechanisms in the Curta are innovative)🎉

[@jdmr4815]

There needs to be a "Pop the doink" t-shirt.

[@antiphlex]

You've certainly popped my doink with this video, Chris. Thank you.

[@MichaelGriffin_]

These are becoming the thing I look forward to

[@davecgriffith]

New year's resolution: work "pop the doink" smoothly into a conversation.

[@trogdorian1]

Happy to say once i figured it out i yelled THATS GENIUS. excellent visual aids!

[@johnsrabe]

That’s why they called him Curt der Krank! Thanks again!

[@LarsTheOctopus]

I wanted to add that subtraction is slightly trickier than that since the stepped drum has to behave differently depending on which digit is actually engaged. Subtracting a number is akin to adding the complement to 9 of every digit, plus one for the last digit, and to discard the overflow. eg. 40 - 12 → 40 + (87 + 1) → 40 + 88 → 128, discard the 1 → 28 The way it is done is via an additional gear on the very last digit (the unit one), which means in subtraction mode every gear grabs as many cog as its 9 complement. The last digit encroaches on the cogs of the line above thanks to its two interlocked gears, so it always grabs one more cog than the others, effectively doing the +1 part. It all is very cleverly done, as this does not impact addition mode, Curt actually recounted that none of the engineers at his father’s company believed it would work until he proved them wrong with a built prototype!

[@PlaywithJunk]

... you just pop the doinc.... I love it!! 🙂

[@LuisRodriguez-vh6fg]

Curta saves my life.

[@Agnes.Nutter]

Yoooo that’s so clever! Can’t wait to learn what other secrets this puppy has in store! :D

[@jamiekawabata7101]

Awesome! I didn't know that about the doink!

[@Beldraen]

Every part doing exactly what it needs. Tour de force in brutal simplicity. I love the Curta design.

[@StephenRansom47]

😅 POPPIN’ The DOINK! … now that is a T-Shirt. Roll the Presses- no doink required. 😉

[@friiq0]

I’ve known about the Curta for so long, but I’ve never seen a video explaining how it works! These animations make it so clear and simple, too. I appreciate the Curta even more now. Great job!

[@pyglik2296]

It's amazing how all of that funcionality fits inside such a small device.

[@HOUHA99]

You're so good at this.

[@Sibicle]

hit this man with that signal boost.

[@getjaketospace]

Curta

[@mpuppet1975]

My new album, "Pop the Doink" drops Tuesday.

[@mpuppet1975]

Mathcore

[@pafnutiytheartist]

Pop the doink!

[@TomCarlson]

Excellent explanation! That flash of understanding, doink, is the best part of learning.

[@mkpleco]

It's Day three, and now I really want this. My home is full of old tech that still works. Including myself.🙄

[@Klaevin]

you know a design is good when you can't imagine how people did things before. Like, I'm now wondering how stepped drum mechanisms work on devices that aren't Curtas

[@Minihood31770]

So now I'm wondering how it carries the 10s, in addition and subtraction. I'll have to wait till tomorrow!

[@Salsmachev]

maybe it's something on the number wheels themselves? I know that's how a lot of simple adding machines do it.

[@RandomBurfness]

But how does this mechanism handle carrying? :O

[@tissuepaper9962]

We'll talk about that later...heh!

[@Pallethands]

Once you pop the doink, you can craink

[@PatrickPease]

I love you sir

[@lafemmedevastation]

huh.. i came here thinking this was gonna be some sort of unique step sequencer drum synthesizer. now that I think about it, the design probably could be applied in such a way if some clever creative had the chops to build such a thing🤔 they better not forget a *solid* MIDI implementation tho😹

[@Vaaaaadim]

2:27 You're telling me the Curta is set up to have one of the gears phase through one of the displays?

[@zalibecquerel3463]

Yo! Pop the Doink!

[@thinkbolt]

The DOINK

[@AJAllchin]

Just pop the doink!

[@febobartoli]

I’ve always loved the Curta design! How often do you get to use your Curta, and does it ever need maintenance or lubrication like a watch or other similar mechanical device?

[@kaisalmon1646]

Pop the doink

[@Lilac757]

For the algorithm.

[@MattMcIrvin]

Does the bit right at the bottom have something to do with the extra +1 you have to do to subtract with complements?

[@LarsTheOctopus]

If you look at the laid out pattern at 3:30 you will notice that in addition mode, top to bottom, the number of steps goes from 1 to 9, while in subtraction mode it goes from 10 to 1. The topmost row is actually only used by the unit digit to do the +1 part. This specific digit is actually tied to two interlocked gearwheels, catching two contiguous rows of cogs. If you add 8, for example, the bottom gear will catch 8 cogs on its row, while the top one will only catch 7 - the row above. If you switch to subtraction mode, the bottom gear will catch an amount of cogs equal to 9’s complement to 8, 1. The top gear will catch the row above, i.e. 2. - in this case, it’s the top gear that is driving, since it catches more cogs. Every other digit uses a single gear that adds its 9’s complement, the unit one does its +1 thing, and there is a separate mechanism elsewhere in the machine to carry.

[@MattMcIrvin]

@@LarsTheOctopus So my guess was exactly upside down!

[@txikitofandango]

If you don't make a t-shirt that says POP THE DOINK then you must not really like making money

[@xremming]

You’re not helping my want of buying a Curta.

[@Salsmachev]

A friendly reminder that you should never pop your doink in public