Hi there - I'd love to help you with this.
I'm a big Apple Watch guy, so I know what is and isn't possible with the platform. First off, Apple Watch unfortunately does not have a magnetometer. So it's not possible to get readings on that front. BUT it does have a gyroscope and accelerometer, and I have made a couple of apps that required reading them.
There is an API called CMSensorRecorder that gets readings from them at 50hz, assuming you're running WatchOS3. (It's 25hz on WatchOS2).
What cloud service do you have? If you don't have anything set up already, I can easily upload the data to a platform like Firebase.
Let me know what you think!
And of course, feel free to take a look at some of my work by visiting my website:
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Thanks and have a great day!
Ben Kelsey