[MOC] Mechanical Calculator

[2GodBDGlory]

I've been enjoying exploring various Technic mechanisms recently, rather than my usual car models, and thought it would be fun to try a mechanical calculator. I know some work has been done in this area by others, but for one reason or another, I tended to skip over reading about such models, so I'm not quite sure what is out there, or whether anything similar to this design exists.

My design was meant to simulate a digital calculator, with buttons for various numbers, and a dial readout.

Overview:

In the end, there were twenty-one controls and three output dials. The first two controls were a simple on/off switch, and a lever to reverse the motor for run/reset capability.

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The third control is a +/- selector, to determine whether the calculator will add or subtract the two numbers.

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Finally, the last eighteen controls are the numbers, with the numbers one through nine repeated twice for the two input numbers.

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The dials included two small ones to display what the current input numbers are, and one large one to show the final answer of the calculations.

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Explanation:

This explanation is probably not very clear, so you may want to just watch the included video!

The calculator had a PF M-motor to drive it, powered from a rechargeable battery and an electrical switch. When running, it would default to not doing anything, and would merely run a number of 16T gears. There were two long axles with a transmission driving ring at one end, and a series of nine parts extending, at the closest approximations to 36 degrees I could get with Lego parts. Essentially, these parts were meant to be equally distributed around 360 degrees, with one gap where a tenth one could be put to complete the pattern.

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Above each of these nine protrusions, there were spring-loaded buttons, which when pressed did two things. 

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First, they engaged the transmission driving ring so that the M-motor rotated that axle, and second, the button moved an axle into a position to stop the axle by bumping into a protrusion (The M-motor would continue trying to rotate the axle, but had a 24T clutch gear to prevent damage to the mechanism). Depending on which button was pressed, the axle would be rotated a different amount. If #1 was pressed, the axle would hardly rotate at all, while if #9 were pressed, the axle would be free to rotate all the way to a fixed stop, or about 324 degrees. The amount each axle rotated was fed to the dials for the input numbers, which read the same number as the button that was pushed.

From here, the amount of rotation from each axle moved into an adder mechanism, using a differential.

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When in adding mode, the two axles drove the opposite sides of the differential in the same direction, causing the differential's output to be greater than it otherwise would have been. When in subtracting mode, the second input number's direction was reversed through a simple, low-backlash gearbox, causing the differential to effectively subtract the two numbers (or, as is perhaps more mathematically accurate, add a negative number).

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Gearbox locked

Forward

Reverse

 

The differential's output, after some strategic gearing, ran the dial with all twenty-eight possible outcomes.

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In the end, the calculator was accurate to about +/- one number, due to backlash in the gearing. Other downsides were its inability to accept more complicated inputs, or to perform more complicated operations, but I think it is satisfactory for a first attempt.

You can see my images at: https://bricksafe.com/pages/2GodBDGlory/mechanical-calculator

 

[Scoar Sonander]

Two things I can say: you need some 3D printed parts, some custom stickers and someone in charge of marketing. You'll be the next (insert inventor of calculator here)! 

But honestly, great work, something my tiny peanut brain could never have comprehended. But with the numbers, aren't you missing a zero? 

 

[2GodBDGlory]

Thanks!

You're right that there aren't any zero buttons, but this is because the calculator assumes it is in zero unless something happens to change it. So basically, if I had a zero button, it would end up doing nothing whatsoever (unless I divided the 360 degrees into 11 equal parts, instead of 10, and added a N\A output as well.

Also, in the original post, I neglected to mention the procedure for resetting the calculator. In order to do so, the motor had to be reversed, and then the two #9 buttons had to be pressed, engaging both axles and letting them rotate backwards until they hit the fixed stop, at zero.

[P McCatty]

This is good. REALLY good. Totally blown away.

[caiman0637]

Wait- this actually works? That's likely the most impressive thing I've ever seen. 

[2GodBDGlory]

13 minutes ago, caiman0637 said:

Wait- this actually works? That's likely the most impressive thing I've ever seen. 

Thanks! This is by no means the first or best Technic calculator, though. This model of Nico71's, for example, looks quite impressive. I plan on building it soon to see how a master of Technic clockwork went about this idea!

https://www.nico71.fr/mechanical-calculator-2/

[piterx]

Thats crazy o.o

[m00se]

Very nice. You might want to check out binary of quaterny (base 4) solutions as that might work better than 10 axle positions.

[DrJB]

Beautiful ... simply beautiful. Are we witnessing Lego Renaissance?

This reminds me of the mechanical registers in use 40+ years ago in some department stores. The cashiers needed some special training as the operation was not too trivial (at least on some models). Think of it as the mechanical equivalent of the RPN logic still used on some HP calculators (if anyone still uses those).

https://www.si.edu/object/national-cash-register-class-51:nmah_694236

Lastly, Thank you for NOT doing yet another 4-wheeled vehicle.

 

[2GodBDGlory]

1 hour ago, m00se said:

Very nice. You might want to check out binary of quaterny (base 4) solutions as that might work better than 10 axle positions.

I'm sure it would be easier, even base 6, 8, or 12 would work better, but I'd still like to keep the calculator in base 10, despite the difficulties.

47 minutes ago, DrJB said:

Beautiful ... simply beautiful. Are we witnessing Lego Renaissance?

This reminds me of the mechanical registers in use 40+ years ago in some department stores. The cashiers needed some special training as the operation was not too trivial (at least on some models). Think of it as the mechanical equivalent of the RPN logic still used on some HP calculators (if anyone still uses those).

https://www.si.edu/object/national-cash-register-class-51:nmah_694236

Lastly, Thank you for NOT doing yet another 4-wheeled vehicle.

 

Thanks a lot! There are a lot of neat mechanisms that can (but rarely are) used in those 4-wheeled vehicles, but I finally realized that the (relative) pain of putting together bodyworks to cover the interesting mechanics was not an integral part of the Technic experience!

The positive response to this model is encouraging me to try to develop my ideas further. I'm pretty sure I know how to remove one of the sets of buttons, and other desirable goals would be allowing for multiple digit numbers, and maybe even adding multiplying/dividing capability, though I don't really have any idea how to do that.

[Ivorrr]

I'm so happy to see creations like that! Posts like these and all the gearbox ones just show there is still so much more to achieve in LEGO technic building!

[aeh5040]

That's an extremely interesting model, always love mechanical computation!  One way to get the required 10-fold symmetry is the drum from here (although it's bulky):

Another random thought: if things were to only rotate one way, perhaps you could overcome the backlash problem.

Edited April 14, 2021 by aeh5040