Check direct current

[pattacini]

We're required to verify that the direct current $I_d$ is kept to $0$ effectively by the FOC PID.
To this aim, we may rely on a temporary hack for the CAN protocol.
To be checked on the setup.

(Aside from $I_d$, it might be convenient to check the bare three-phase currents too.)

cc @Nicogene

[pattacini]

cc @maggia80 @fiorisi

[mfussi66]

The Id could be quite easily inserted into the STATUS message payload without removing other quantities, there is still plenty of space and it can legitimately be useful info:

[pattacini]

For the time being yes, certainly, but in the mid/long term that message is already allocated. See #15.

[pattacini]

Provided the reading of the direct current in the test branch https://github.com/robotology/icub-firmware-models/tree/test/direct_current.

The format can be retrieved from below:

cc @mfussi66

[mfussi66]

Today, we successfully measured the direct current Id on CAN as above, and confirmed its truthfulness when printing the 3-phase current on the firmware debug viewer.

Here is an example:

Id is correctly controlled to 0 on all three boards. As highlighted above, however, the closeness of the hall sensors of AMBCLDC 0 to the motors influences readings.