Need help adding RPM Sensors to a quad

Hello I am trying to figure out what is the best option is for and RPM sensor for the Cube. I have come across one forum where a guy was using a Arduino Nano with a Hall effect sensor but it was only 1. I would need a sensor on 4 motors. Does any one know of a normal RPM sensor that works with the Cube? Also is it possible to get RPM readings for 4 motors?

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Can Ardupilot even accept 4 inputs? You may need Ardupilot code.

What is the goal?

just trying to RPM readings from all four motors. I need to be able to see the logs over time in either the Tlogs or the stored logs on SD card. If I could get RPM readings from at least 2 motors that would work also.

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There is a limitation in ArduPilot for just 2 RPM sensors. Hopefully with in the future with Bi-directional D-shot on the roadmap more RPM sensor instances will be supported. Battery sensors went from 2 to 10 instances so it might be possible.

We’ve used hall effect sensors for RPM before. A carrier board that provides at least 2 AUX channels (normal is 6) could be set up for 2 inputs and then each of the inputs set as an RPM sensor. Usually just AUX 5 and 6 are set as inputs by default.

BRD_PWM_COUNT=4 would get 2 GPIO pins on AUX 5 and 6.
RPM_PIN=55 for AUX 6
Set the rest of the RPM as you need and likewise for RPM2_x.

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Thank you for the info. I’ll give it a shot and post how it comes out.

@TunaLobster hey is there any hall effect sensors that you recommend?

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I have not had to buy sensors for RPM before. Usually they are already on the output shaft of the engine for timing purposes and the same magnet can but used with a sensor the engine manufacturer provides.