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The first mechanisms considered were locomotive valve gears. A valve gear is a device on a locomotive that enables a steam engine to be throttled and reversed. An example of one of the most well known valve gears, the Stephenson Valve Gear is shown below. By adjusting the a lever on the locomotive, one is able to vary the stroke of the valve rod which determines the flow rate of steam through the valve.
Valentine[1] modified a valve gear mechanism to be used as a wing stroke controller for As can be seen in the diagram below, valve gears tend to be very complicated mechanisms and output a linear oscillating motion instead of the rotary oscillation need, making them ill-suited for use in this project.
However, valve gear mechanisms have been modified to be used as steering mechanisms for ornithopters, where the mechanism is used to modulate the wing stroke on both sides of the ornithopter much in the same way we intend to steer. A mechanism designed by Valentine is shown below.[1] While this mechanism has the advantage that it directly outputs an oscillating rotary motion of a link with a decent mechanical advantage, it is very complicated and requires linear actuators for stroke adjustment.
Another mechanism we considered was a hypocycloidal variable stroke mecha
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The next one is a variable piston stroke mechanism used in automobile engines and uses a linear actuator to move a pivot point along a circular path to modify the stroke of a piston.
Sources:
- A Variable Stroke Mechanism for Ornithopters
- Fixed Frequency, Variable Amplitude (FiFVA) Actuation Systems for Micro Air Vehicles