icub3: fix the feet's ft measurement direction

[Nicogene]

We noticed from the cad that the FT sensors in the feet are mounted upwards, and in the arms are mounted downwards, and following what the wiki states (see https://wiki.icub.org/wiki/FT_sensor) in the feet the direction are parent_to_child

Ft in the arm

Ft in the feet

Please review code

[pattacini]

cc @prashanthr05 @S-Dafarra

[traversaro]

As a final check, it would be a good idea to check how the FT sensors are mounted on the iCub 2.5 (based on the yaml configuration in this repo, I would suppose that the are mounted as in the arm).

[traversaro]

As a final check, it would be a good idea to check how the FT sensors are mounted on the iCub 2.5 (based on the yaml configuration in this repo, I would suppose that the are mounted as in the arm).

In any case, this can be done after the merge.

[Nicogene]

As a final check, it would be a good idea to check how the FT sensors are mounted on the iCub 2.5 (based on the yaml configuration in this repo, I would suppose that the are mounted as in the arm).

Checking the yaml seems so :

https://github.com/robotology/icub-models-generator/blob/master/simmechanics/data/icub2_5/ICUB_2-5_BB_simmechanics_options.yaml.in#L610-L637

And I can confirm it also CAD side

Ft in the arms

Ft in the feet

[traversaro]

So, working to have the measured_direction in SDF back in gazebosim/gazebo-classic#940 and removing the hard-coded assumption that the direction of the FT sensor was always child_to_parent that we had in iDyn turned out to be useful in the end, as at some point we used another mounting direction for our FT sensors. :D