An oscillating cylinder steam engine (also known as a wobbler in the US), the Wobbler engine is a simple steam engine design that requires no valve gear, which makes manufacturing quite simple. And because of that, the Wobbler is usually the first type engine made by small engine builders.
Wobblers are more compact than other types of cylinder of the same capacity and they have the advantage of simplicity and, therefore, low manufacturing costs. They are now mainly used in toys and models but, in the past, have been used in full-size working engines, mainly on ships and small stationary engines.