GerhardHippmann

Arbitrary online measurements are implemented in [frameMeasurements.jl](https://github.com/ModiaSim/Modia3D.jl/blob/main/src/Composition/frameMeasurements.jl) and are used in force elements, e.g. [Bushing.jl](https://github.com/ModiaSim/Modia3D.jl/blob/main/src/Composition/ForceElements/Bushing.jl). I think the simplest approach would be to modify or copy an existing force element.

Yes, you can also use flanges of prismatic and rotational joints, like `speedSensor` in [ServoWithRampAndRevolute.jl](https://github.com/ModiaSim/Modia3D.jl/blob/main/test/Robot/ServoWithRampAndRevolute.jl). But this is rather [Modia](https://github.com/ModiaSim/Modia.jl) stuff and restricted to joint state variables.