Post about your Basic project here

Moderator: Mmiscool

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By forlotto
#50671 Interesting I can think of underwater motors this would be useful for...

Other things may be underwater turbines for electricity generation in which case the entire unit may be submerged ...

Hrmmm yes this would likely be best done in a water tight enclosure but there may be other reasons to want one that will function underwater I wonder if a plexiglass enclosure all sealed would allow it to get an accurate reading as I am sure they make water proof terminals that you could use for your wiring if need be if you mounted the case in the correct spot maybe you could get a reading.

Maybe they make an underwater tachometer ? might be a better route?
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By fsae99
trackerj wrote:Why do you want to measure prop speed IN the water? Usually is done inside the boat (or inside the outboard motor case) on the propeller shaft. Any optical encoder or hall sensor can be good for a basic setup.

This is an electric motor. Only the sensor need be in the water. Unlike an airplane propeller that reaches its max speed in the air while pulling the max draw of amps boat props are essentially free running in the air (no load).

The equation prop pitch *rpm*60 / 63360 will tell you the max speed possible.

In an outboard you measure the motor rpm and you know the gear box ration and you do the math.

I have burned up the 2 IR LEDs I had on had, 1 due to water intrusion and 1 due to my mistake (connected straight to 5V instead of Volt Divider).

I will be ordering more and a Hall effect sensor.

Why am I trying to do this externally, because opening the motor fitting sensor and resealing is problematic.