Push-pull NAND & OR gates

"No, no, you're not thinking; you're just being logical." - Niels Bohr

The OR and NAND gate related, one is simply the other with NOTd inputs, which is why they're both on this page. The OR gate is shown first, followed by the NAND gate.

The OR gate

The OR gate was the first logic gate I designed that actually does something. I decided to make the OR gate after the NOT gate because with these two you can make NAND, AND, and NOR gates.
The key mechanism in the OR gate is the rotation of one of the cross-beams. This allows either input rod to go back or forward, separately, without changing the position of the output rod. The fixed cross-beam at the other end of the shaft will move forward regardless of whether it is pushed by one or both input rods. The four input and output states are shown on the figures below.
The LDRAW/MLCAD model and step-by-step instructions on how to build the model are available for downloading.

The simplified OR gate

Using the simplified NOT gate as discussed on the NOT gate page it has been possible to simplify, by quite a considerable amount the OR gate. The following four photos show the new OR gate in its four different states.
And if you're keen to see it in action there is also a video available to watch.

The NAND gate

Logically a NAND gate is the same as an OR gate with NOTd inputs. This is a very useful equivalence. There are two ways I could have done this to my OR gate. The easiest is to use the NOT gate at each input. The other way was by recognising that to NOT the inputs just requires an extra cog in each gear train, to reverse the motion of the racks. This should be clear from the four logic states shown in the photos.
Unfortunately, by using extra cogs, the gate suffers from the tiny amount of slack in the gears. This reduces the linear motion of the push-rods to the extent that after two gates in series everything grinds to a halt.
The LDRAW/MLCAD model and step-by-step instructions on how to build the model are available for downloading.

The simplified NAND gate

I've since simplified the NAND gate by making use of the single cog NOT gate explained on the NOT gate and buffer page. The result is that I can get rid of the additional 8-tooth cogs, which led to the problems explained above. The NAND gate can be simplified even more allowing the other 8-tooth cogs to be removed also. This should be clearer in the photos below and from the video.
And if you're keen to see it in action there is also a video available to watch.