I am attempting to come up with plans for a bar speed tracker, the most famous of which is probably a Tendo Unit. As the name would suggest, the short description is that you attach a sensor to your barbell and it measures the speed with which it is lifted/moved. Once you have that info, you obviously have the ability to do some maths to calculate force, power etc. I've attached a video of another person's home-made version for those of you who want to see it in action:
I'm confident in my ability to build and program it but I'm struggling to come up with a name or search term for the sensor. As you can see in the video, it is a cable which I assume connects to a spring loaded potentiometer or rotary encoder but I don't know if this sort of thing comes pre-built. Any suggestions or help locating this would be much appreciated.