These parameters allow restricting the output of high-level controllers - the position PID, velocity PID, and
impedance PD controllers. These limits are applied before the max current limit, so even when set high they
will not lead to a hazardous situation until the max current is fixed at a safe level. The max velocity limit is
respected only in position PID mode, whereas the max torque limit is respected in all motion modes. Check
out the c
for more information.
Note: if the torque bandwidth is set to a low value it is possible to read torque values that are above
limits when external torque is applied (for example during impacts). This is only true in transition
states - when the load is constant the limits will work as expected. This is because with low torque
bandwidth the internal torque PI controllers may be too slow to compensate for rapidly changing
torque setpoint when hitting the torque/current limit. If you care about accurate torque readout be sure to play
with the torque bandwidth parameter and possibly increase it from the default level.
2.6. FDCAN Watchdog
MD80 features an FDCAN Watchdog Timer. This timer will shut down the drive stage when no FDCAN
frame has been received in a specified time. This is to protect the drive and its surroundings in an event
of loss of communications, for example by physical damage to the wiring. By default, the watchdog is
set to 250ms. This time can be set to any value in the range of 1 to 2000ms using
mdtool config can
command. When the watchdog is set to 0, it will disable the timer, however, this can lead to
dangerous
situations
, and it is
not a recommended way
of operating MD80.
Warning: we do not recommend disabling the CAN watchdog timer.
2.7. Measurements
MD80 is equipped with sensors that allow for measuring the motor position, velocity, and torque. Whether
the motor has an integrated gearbox or not,
the position, velocity, and torque are in the output sha
reference frame
. This means that changing the position from 0.0 to 2
𝞹
radians, will result in approximately
one rotation of the motor for direct-drive (gearless) servos and approximately one rotation of the gearbox
output sha for geared motors.
Position
To measure the position of the rotor an MD80 uses an internal magnetic encoder. The resolution of the
encoder is 14 bits (16384 counts per rotation). The drive aggregates all the measurements to provide
multi-rotation positional feedback
. The reference position (0.0 rad) is set by the user and stored in the
non-volatile memory. Please see
mdtool config zero
command for more information on how to set the
desired zero position.
Note: When using geared actuators with gear ratios above 1:1 it is not possible to determine the
position a er startup unambiguously, since the motor completes multiple rotations per single
rotation of the output sha . For example, for a 2:1 gearbox, there are two sections within a single
output sha rotation where the motor sha is in the same position. Unless the motor is placed in the wrong
“section” during startup the absolute encoder functionality will work.
Velocity
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