This model has no beam. The original was constructed by Richard Trevithick. From 1798 he found a lot of new solutions. His engines utilized high-pressure steam, they didn’t use condensation, they had a so far unknown boiler design, even Watt’s or Evan’s linkage was not used. For further details see here.
The scale of the model is 1:16. I used the plan published by Tubal Cain alias T.D. Walshaw in Model Engineer #3809 1987. I recalculated the measurements to fit metric bar stock etc. Like Walshaw I run the model by compressed air.
The aforementionend boiler construction was not the only innovation: The feedwater heater was another improvement.
The Dredger Engine was technically quite mature. Trevithick’s Dredger project was no real success, but the reason was the bucket chain, which seems to have been the root cause for a lot of trouble. In other applications the engine performed quite well 1.
While I was at work, Julius de Waal made a new metric plan based on Tubal Cain’s original 2.