Mechanical computers and old toys

Tinkertoy
''The Tinkertoy Construction Set was created in 1914...'' [source]
It can be used to:
- make robots [source]
- or even compute! [source]

''In 1975, when Hillis and Brian Silverman were in their sophomore year, they participated in a class project to build something digital from Tinkertoys. The students sat down to play. One made an inverter a logic device that converts a binary 1 signal to a 0 signal and conversely. Another made an OR gate; if either of the device's two input signals happened to be a 1, then its output would also be a 1. It quickly became clear to the students that Tinkertoys were "computation universal," ...''

In fact logic gates can be implemented in other supports than electronics.
See here: [fluidics]
Also here: [bubble logic]

You can use rods (or strips of paper) to calculate: [see here]

And this is the complete schema of the DigiComp I and II mechanical (toy) computers:
[source].

For more DIY projects about mechanical computing machines, see [here].