The diaphragm-type of pop-pop engines can be used for more purposes, as shown below.
Step 1: The Diaphragm Pop-pop Engine
A pop-pop steam engine can move a toy-boat with his thrust, there are numerous examples and descriptions for that. But to carry out as a steam engine, for rotating, or alternating motion it can be an expressive example for demonstration. The slide-valve falls off, therefore comes a pulsating water snake, the piston is replaced with a diaphragm, the engine will be an athmospheric type. The slide valve on a steam engine is mechanically connected with the piston, but on a pop-pop engine not. So it is problematic, if there will be a regular motion of the diaphragm, or not. The practice shows, it is not regular. The frequency and amplitude of the diaphragm is unsteady. Theoretical the elastic loading of the diaphragm increases the inside pressure, and the thrust, but we can only observe experimental, if the totalised power gets bigger, or not. The motion of the diaphragm will be slower, when we use a silicon plate, so the motion can be showed better. For a strong steam drum we made it hard-solded with the pipes, and the flanges are from 2" pipe-nuts, with turned planes, and skrew-holes. The hot smoke is drawn off the diaphragm, a little chimney is put to the engine. The burner is a simple spirit-lamp.
Step 2: Boat With Paddle
There is a boat, wich has a paddle, moved from the diaphragm, and improves the propulsion. A mechanical transmission conducts the power of the diaphragm to the paddle.
Step 3: The Yaw
The motion of a yaw (punkah) is also alternating, so we can try to make a little ventilation with it.
Step 4: Stable Engine
As a stable engine it must not swim, the water can be in a vessel, (two balloons in the example), and the alternating motion can be transformed with a ratchet to rotation. This version is working good, but you need bigger balloons, to have good cooling (on the picture are only little air-balloons, and have not low temperatures).
Step 5: Summary
The pop-pop engine experiments can support the presentation of a steam engine. The spectacular results can hep the understanding of the construction.