"Joe Gwinn" wrote in message
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If the motor runs slow, so does the oscillation cycle, in direct
proportion.

Joe Gwinn
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If the expected fatigue life is 2 million cycles, the test time at 1 cycle
per second is three weeks. I think a good solution would be a closed loop
based on a pressure sensor that shows when the high and low limit pressures
have been reached, so the controller can switch between the fill and dump
solenoid valves as rapidly as fluid flow permits.

If I had to build a prototype of the tester the controller would be an old
laptop (or desktop) with a printer port, the data bits driving a
successive-approximation A/D converter to measure the pressure sensor and
two control bits operating the fill and dump solenoid valves.

QBasic running in DOS gives full unhindered access to all of the printer
port bits for input and output, unlike Windows. An Arduino could also work
but the laptop has the advantages of a huge hard drive to store data, the
keyboard for control, and the LCD on which QBasic can display the cycle
count and a graph of the pressure.
http://www.nicolasbize.com/blog/30-y...till-the-best/

This simple resistor network outputs a voltage proportional to the binary
code from the port bits:
https://www.tek.com/blog/tutorial-di...rsion-r-2r-dac

The other electronics are an analog comparator (LM311) driving a printer
port status bit that tells if the sensor output voltage is more or less than
the DAC output, and the two high current solenoid valve drivers.