The velocity is estimated by measuring position change in time, at a frequency of 40kHz. The measurements
are then filtered using a low-pass filter with a cut-off frequency of 5 kHz since the position differentiation
method introduces noise.
Torque
Actuator torque is estimated by measuring motor phase currents. This method can be used on low gear ratio
actuators (preferably below 9:1), that are easily back drivable, to get an estimate of the torque applied by the
motor. In applications with higher gear ratios, the torque readout might be not as accurate due to excessive
friction in the gearbox.
2.8. Calibration
Calibration is performed when the MD80 controller is first mounted to the motor. It has two stages during
which it measures specific parameters of the setup.
Note: the calibration has to be performed on a motor that is free to rotate with no load attached to its
output sha . If the calibration fails, you will see errors when executing the
mdtool setup
diagnostic
command. If the failure is essential to the motorʼs operation the MD80 will remain
disabled till the next calibration attempt.
Encoder eccentricity
Encoder eccentricity is the first measurement that takes place. During this part, the motor performs a single
rotation in both directions to assess the amount of error due to non-axial encoder placement.
Torque bandwidth
Even though the torque command on MD80 controllers seems to be applied instantaneously, in reality, itʼs
not the case. As in every system, thereʼs a response to the command which depends on the system itself and
the controller gains. A parameter called bandwidth was introduced to describe how fast the output of a
system reacts to the changing input. Calibrating the motor for a certain torque bandwidth requires
measuring motor parameters. This happens in the last stage of calibration and it manifests itself as an
audible sound.
The torque bandwidth is set to 50 Hz by default. It can be set to anywhere from 50 Hz to 2.5 kHz,
however it is important to note that higher torque bandwidth causes a higher audible noise level. Please see
the
mdtool setup calibration
command for more details on calibrating the actuators.
When the system that youʼre designing is a highly dynamic one, you want the torque bandwidth to
be higher than the default setting of 50 Hz. Start by calibrating the drives for 1 kHz torque bandwidth, and if
you see this is still not enough you can increase it further.
3. CANdle and CANdle HAT
CANdle is a translator device used to communicate between MD80 controllers and the host device. Currently,
there are two CANdle versions - CANdle and CANdle HAT.
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