Optical vs Magnetic Tacho...

[Hell-e-Guy]

Hi Guys,
After finishing a recent project, I now have time to start designing an
on board tacho for my heli.
The question is what's better....an optical sensor or a magnetic one?
I will be using a Cypress PSoC micro-controller with on board op-amps so amplifying and filtering of the signal is not a concern in both case....

Thanks.

[Tophinater]

if its going onboard the heli, I would suggest magnetic.

[lazy-b]

Magnetic is a lot better, its very reliable, its dirt resistance, but its a little bit difficult to install 2 small Magnet on the Fan, need to drill 2 holes and need to epoxy the 2 magnet........Futaba Governor GV-1 use Magnetic Sensor, but have saw others using Optical Sensor.

saw somebody have crash their helicopter due to optical sensor governor, cause SUNLIGHT can effect the optical sensor .

For Simple Tachometer only, just monioting Rotor RPM, I guess, Optical is more simple to implement just need a simple Photo Cells.

[Hell-e-Guy]

Guys U Rock !!!
Thanks for all the answers...
never thought of the dirt problem with the optical sensor.
Can you please give me some magnetic sensor / pickup part numbers so
I can get started.


Man I Love this Forum !!!

[lovefool]

I am currently working on the project that use magnetic tacho. A magnet is already installed on the gas engine shaft for ignition purpose. So I have installed a hall sensor from Allegro and read the signal by PIC. There is only one magnet, so I thoght I will not get good resolution when I read count per certain window (6000rpm->100hz-> 100 pulse per 1sec) . So I have decided to measure the interval between two pulses. It looks working fine.
http://www.allegromicro.com/hall/

[Tophinater]

If your going to use a magnetic pick up using a hall sensor and then having a PIC do what ever, I would try and do it with two magnets. "Technically" one magnet would be more accurate but you will get more proper balancing with two.

As for parts, I dont know any off the top of my head but I bet you could get everything you need from www.jameco.com. It might be easier just to hack a bicycle tach for what you need. I dont know if you looking to transmit the speed or anything then you probably wouldnt want to go that rout.


You dont nesseccarily have to use optical or magnetic either. You could doing an actual mechanical tach using a cam and switch or if you dare using the wire kind like on cars.

[paulg]

Is there a metal gear in the gear train? If so, use an inductive sensor.

[vintage1]

Yup. Coil over magnet works well, as guitar pickups..

[xxrando]

Would it be possible to monitor one or more of the motor input wires (brushless) and avoid optics and magnetics completely?

[Hell-e-Guy]

Guys, thanks again for all the help!!!