One-Crank Steam Engine

One-Crank Steam Engine

All the other steam engine models I sell (and nearly all other steam engines, whether model or full-size) have one thing in common: they have two crank arms or eccentric take-offs from the flywheel. As explained in the description of the Right-Angle Steam Engine, this is because the valve needs to be moving fastest just as the piston comes to rest at the end of its range of motion (to switch the steam pressure over to the other side).

This design uses a sort of mechanical hack to synthesize an acceptable (or perhaps even superior) valve motion from the motion of the piston, eliminating the need for a second crank arm on the flywheel.

As described in more detail in the Right-Angle Steam Engine description, you can think of the motion of the piston and valves in a typical steam engine as following, respectively, sine and cosine waves. The graph here shows how these two curves have the property that when one of them is turning around at the top or bottom of its range, the other one has is steepest slope (fastest motion).

The valve in this one-crank model follows a more jerky curve, which is basically the crest of the sine wave of the piston amplified (by about a factor of five), and then allowed to remain stationary by the gap in the linkage on top of the piston. This actually allows the valve to switch the steam pressure faster than any of the other designs, but at the expense of jerky motion that would introduce noise and wear to the mechanism.

Your model will arrive attractively packaged with all the necessary parts (even a screwdriver). The kit screws together in about 20 minutes, and does not require any special model-building skills. A detailed, step-by-step assembly video is available on our instructions page.