Based on a comment from a visitor to the space, compressed air is freely available at petrol stations (until it is no longer freely available) and can be used to drive an engine mechanism for other purposes.
There are several designs under consideration:
Based on this design which uses smaller cogs on the radius and a fluid pressure on these outer cogs to induce rotation which is in turn transferred to the inner drive wheel. I like this design as it is able to be cut from a single sheet which aids prototyping. It would also look nice with a clear perspex cover (probably reinforced)
Design only. Looks like this:
Design and prototype. This extends the design to include 4 small cogs like this:
The problem with this design is that all cogs are in phase, similar to having a 4-stroke engine where all cylinders are firing at the same time. The prototype also raised an issue where the contact between the cogs was inefficient at a certain point in the cycle. See below the yellow line approximates the line of contact, the red line displays the force transferred to the drive cog, while the blue line shows the preferred line of force. In the prototype the design tended to stick at this point.
The proposed solution is in two parts:
Relating back to the reference design, the inner cog should disconnect early from the outer wall then reconnect late on the small cog in the high pressure area, then disconnect late and reconnect early on the low pressure side.