For a thesis project for ways to localize a slide on a linear rail with a length of ~1m. The slide in question is the seat of an indoor rowing machine: Concept2 Ergometer Price is definitely an issue as we want to built multiple sensor setups.

I need the location of the slide with an accuracy of around 1mm with a rate of 50-100Hz. Adding cables to the seat is something I want to avoid, so I'd like to have an external sensor (fixed to the rail) and at most a target (e.g. reflective surface) on the slide. Seat speed can be up to 2m/s.

I thought about Sharp triangulation sensors (like the GP2Y0A60SZ0F), but I have no experience with the accuracy and its behavior with fast moving objects. Even when operator with 5V, the output for 50cm and 1m only differs by 0.25V so I assume that there is a major accuracy degradation.

Ultrasonic is to slow and inaccurate, and commercial laser triangulation sensors are quickly at >200$.

Which sensor principles am I missing? As soon as I know what I'm looking for, I can find a sensor on my own (no shopping question!), but I can't search for a sensor if I have no starting point.


1 Answer 1


Have you thought about a linear encoder system (wiki)?

I am not sure whether it is cheaper though.

  • $\begingroup$ Welcome to Robotics Brent. Thanks for your answer but we are looking for comprehensive answers that provide some explanation and context. Very short answers cannot do this, so please edit your answer to explain why it is right, ideally with citations. Answers that don't include explanations may be removed. $\endgroup$
    – Ben
    Commented Sep 21, 2019 at 12:52
  • $\begingroup$ The sensor would solve the problem, however it would require a cable to the seat which I'd like to avoid. $\endgroup$
    – FooTheBar
    Commented Sep 23, 2019 at 8:02

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