How fancy the timer needs to be depends a little on how fancy the ESC is.

Back before the governor mode of the ESC became ubiquitous, the normal voltage drop of the battery was compensated by the timer ramping up the throttle during the flight. This keeps the lap speed nominally constant. I use this mode on my 1/2 a models where  was trying to make a simple cheap (no governor-mode ESC), and there it works pretty well---these planes tend to fly ballistically anyway!

With governor mode, the timers can be really simple---unless you want some rpm trim capability.

I guess we can always want more!!!

I've been making some tests on one of these timers, using an oscilloscope. It is a nice, compact, professionally-made unit, wrapped in plastic. It uses a tiny (surface-mount) version of the microcontroller used by Igor in his first timer, the PIC 12F675. I found that it pretty much works as advertised.

Upon powering up, it put out a 1.022 ms signal (throttle off) at 45.9 Hz. During a run, it can be adjusted between 1.006 (throttle really off) to 2.038 ms (a little more than the nominal 2.0 ms for full throttle). The instructions state that "Approximately 3 seconds before the motors begins to gradually slow down, the cut-off alert will occur. This is a very brief reduction in motor rpm. This signals that the motor will begin to slow down to a full stop within 10 seconds." It does slow down and quickly go to throttle off, starting almost immediately after the momentary low-power warning; no wonder this isn't very helpful in escaping from anything more than level flight, since most timers return to full power for 5 seconds or more after the warning.

It was easy enough to set the flight time (one minute for each sudden spike of throttle), but it is restricted to whole minutes and it has to be done every time you fly. The run-up to flight power starts almost immediately thereafter -- not good if you still have to get to the center of the circle. Another curious property: Although it can be stopped (to 1.0 ms) at any time during the "flight" time by pushing on the button, it also can be re-started at any time (to the throttle spikes and flight timing) after a flight is over -- potentially a hazard if you accidentally push on the button.

Since it uses a standard ESC (which doesn't have a constant-RPM function), it can be easily replaced by a timer that implements a throttle advance to compensate for the decline in battery voltage during a flight, as well as better flight management, if desired. I'm planning on bench testing the timer with the larger of the two motors recommended for the PT-19.

Inexpensive isnt neccesary low quality, in my case it was lack of features. The ZTron Simple timer seems to be a high quality product, the thing I didnt like was the short arming sequence (5 seconds) and the lack of a dedicated start button. I now build my own timers and get the features I want. However, if I would buy a timer it would most probably be one from Mr. Hubin. From what I understand, Mr. Hubins timers dont have small DIP switches and complicated setup procedures, but instead use potentiometers to do the setup (way much better in my opinion).

Just my $0.02

Andreas