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Another LEGO Technic prototype made to try a mechanism in practice before adapting it to my own materials. I wanted to use one of my pull back motors for a track inspection vehicle (speeder) or draisine and had various designs in mind, only to recall something both more iconic and (IMO) more interesting: a pump trolley/handcar [can't believe that's the first mention on the entire site...]. I remembered Lionel makes infinite versions with all sorts of riders on them - even Woody and Buzz and the elves from The Polar Express - and thought to look up how one of them operates. The official diagram looked very complex and didn't quite help me understand. I then found GIFs and a video showing (more or less) how real ones work and found this one, which looked a lot easier to follow. Recreating exactly what I saw didn't give the right range of motion, and it proved a bit frustrating changing the height and not knowing what I was doing wrong.
However, it occurred to me that as early as 1994, the LEGO Group made their own Technic design as one of the models in Set #8062. In that version, the arm is attached near the very edge of the walking beam so it could move equally at both ends. In spite of a minor creative liberty (the distance between the gear and attachment point), it turned out highly successful and works much like the real things. I also tried building an articulated rider for it, though it ended up causing some trouble and the idea was scrapped. I hope any versions with "normal" materials could be as reliable as this, which will allow me to make some with (original and existing) characters that Lionel never used.