I worked with Eric Rule to provide a custom timer for this "turnkey" electric propulsion option, starting with his choice of the Hacker motor and Hacker ESC and prop. Initially, looking for the simplest and most user-friendly system, he suggested a timer that would only use 9100 RPM as the governed RPM for a fixed flight time of 6:20. We ended with a custom timer that can be adjusted (via two onboard pots) from 9100 to about 9900 RPM and for flight times from 2:05 to 6:20. Because I measured the (switching) BEC voltage from the Hacker ESC to be slightly greater than the power supply of 5.5 volts specified for my microcontroller (see previous thread), I customized the timer to include a dropping diode.
Eric didn't include an arming plug, which I recommend. However, all the timers I supply have the start button remoted so that they can be mounted on the outside of a fuselage airplane. The motor can't start until the ESC has received a few seconds of throttle "off" pulses (1.0 ms) from the timer, and then not until the start button is pushed.
As usual for my timers, the RPM can be adjusted during the first minute of "flight" time, the motor can be stopped at any time with another push on the "start" button, and the voltage to the ESC goes from the throttle "off" pulse width to zero volts some 30 seconds after the flight has ended, to make a restart impossible.
To make the simplest timer, the timer blips the motor a second after the start button is pushed (to confirm that timing has begun) and then waits 30 seconds to begin the flight time/flight RPM. To keep it simple, the RPM pot is preset for 9100 when fully counterclockwise and the flight time is 6:20 when the TIME pot is fully clockwise.
I have bench tested the combination but haven't yet installed it in an airplane.