The YA-1 was the first motorcycle manufactured by Yamaha, from 1955 to 1958, though its design was heavily influenced by the pre-war German DKW RT125, and its numerous post-war derivatives. It had a tubular bicycle-style frame carrying a 125cc two-stroke engine like the RT125, but differed in having springing on both front and rear forks.
The model is the latest, and apparently the last, model published by Yamaha Paper Craft. It was brought out in December 2017 amid much fanfare, to celebrate the 20th anniversary of their paper model web site. Given this enthusiastic promotion it was a major surprise to see them announce only six months later that the site would be closed at the end of September 2018. The model is billed as being in their "Ultra-Realistic" series, though it is to an even larger scale than the others in the series. No scale is explicitly given, but the overall length of the model is cited as 49.5cm and Wikipedia lists the prototype as being 1980mm long, so we get a scale of 1:4.
The model is supplied in three PDF files, with three corresponding files of assembly instructions. It comes in two different versions : "standard" and "special". These appear only to differ in the treatment of the drive chain and the wheels. For the latter the standard version has rather oversized spokes made of paper, while the special version has formers for making the spokes from a length of thin cord.
The YA-1 was a much simpler vehicle than the superbikes of the other Ultra models, and the model is similarly much simpler. Each version totals 34 pages of parts, with about 650 parts for the standard and 570 for the special. Almost all the extra parts are the 72 separate paper wheel spokes.
As usual I have reduced the model to 1:14, a rather extreme 3.5:1 reduction. This has meant a good number of changes to the construction methods to make it feasible, but I have made the result as true to the original model as I could.
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