Detecting the currant rotation of a free spinning globe

[moonhermit]

Hello, first time poster. I recently got into Arduino and have a question about my approach to the problem I am trying to solve.

I want to measure the current rotation in degrees of a free-spinning object based on a relatively forward position. The rotating object, (a globe) needs to be able to spin freely along its single axis and lose its momentum gradually after it stops being actively pushed.

My solution is to use a stationary magnetometer, (specifically the MLX90393) in the object's axis and attach a magnet on the inside of the object that rotates with it, acting as a moving north position. Relative to the magnetometer this should function the same as rotationing the magnetometer itself.

My question is this. Is this a good solution? Am I overcomplicating this? Is there a simple component that fits all my needs such as a free spinning rotary encoder I am unaware of? Would this solution even work in the first place or have I fundamentally misunderstood how magnetometers work?

I originally thought I could use a rotary encoder to achieve this, having it act as the object's axis but I have been unable to find any that allow for free spinning.

Thanks in advance. Hoping I haven't made a fool of myself here.

[jremington]

@moonhermit

Is this a good solution?

Yes, if you can determine the orientation of the globe to your satisfaction.

Absolute rotary encoders would work too. One with a bearing and shaft extension could replace the shaft and bearings shown in the drawing, and models using magnets reduce shaft friction to the vanishing point.

[johnerrington]

That seems a good solution. The magnetic field may be disturbed by the surroundings and external mag fields, but i think you could resolve that in the software. There are alternative solutions such as an optical encoder but at the price I'd say its worth trying.

Adafruit Wide-Range Triple-axis Magnetometer - MLX90393

[jremington]

For a different noncontact method, take a look at the mechanism used in this video:

Interactive Digital Art - 'rotary tumble'

[dougp]

@moonhermit

I originally thought I could use a rotary encoder to achieve this, having it act as the object's axis but I have been unable to find any that allow for free spinning.

What about a magnetic rotary shaft encoder at DuckDuckGo?

[hammy]

A magnet may upset the balance of the ball and make it spin less .
I would use a piece of reflective tape and an optical sensor .
Google reflective sensor .