Interfacing mechanical tachometer with Arduino?

[SimSupervisor]

[hyamesto]

Congratulations:
You have a real working tachometer, and I´m happy to see working full (with the time recorder too).
Try to fix the motor and the shaft, keep it as straight as possible (curves no more than 90º).
For your information, I´m a real civil pilot, flying a Cessna 172, and don´t worry by erratic readings under 700 rpm.
In the real plane, it´s very rare having the motor running under 1000 rpm. As I say before, the tachometer it´s non lineal response, at more rpm, more torque you need, but is easy to programing a function to correct that error.
Again, keep the good work.
Regards.
Horacio.

[hyamesto]

Other thing, you can use a gear train to increase the revolutions of the shaft, and you can use the DC Motor with more RPM.
Remember, the max RPM are marked with red line in the tachometer (2700 RPM), and its very rare exceed this value in normal flight, except with full throttle and nose down to the ground. (like kamikaze....)
Regards.
Horacio.

[SimSupervisor]

I got a second DC motor at the electronic surplus store today, thinking it was a 5500 RPM (that's what they said at the store) but it was likely 8800 or something like that; when applied a full PWM the tacho was doing a full turn before going back to 2700. Its rather impressive, but totally not what I am looking for. lol. I think I'll stick with the motor I have on hand; it goes up to about 4000 RPM, unless I get an interesting gear train the current motor is very adequate. I'll try to work on getting a better corrective equation, and be set.

Thanks a lot for your take and info about the cessna 172. The panel I am trying to populate is based on a cessna 150 so there are quite a lot of similitude. There are more instruments for me to work on...

[SimSupervisor]

I forgot to add: I am quite happy to get the hour recording function. I never planned to have one and it isn't a necessary function of the simulator, but now that I have it, its going to be something fun to track.

I looked about trying to reset the numbers, and unless I dismantle the unit this wont be happening. So, when I install the simulator, I'll note the "hours" and just count from there.

[hyamesto]

You can do one thing more to zeroing the hour recording counter:

Leave running the motor for 319 days. 6 hours, 20 minutes, 25,66 seconds....

Regards.
Horacio.

[SimSupervisor]

Yes, I thought of that.

But I wondered what would happen if I leave it on about six minutes too long...

[SimSupervisor]

Good news of the day!
I found out why it was stutering at low speed. The PSU wasn't OK with the motor's low speed revolution power peek. I plan on using the computer's PSU to power the avionics, so I went ahead and used a computer power supply unit.

After measurments, I made a graph of what my motor does at specific PWM values

and from there I toyed with math until I made up something that was close enough. It still have some overshoots below 1300 and over 2900 RPM, but is very close to precise in the most important zone of 1400-2700 RPM - I don't think I'll tweak it any more than that.