7
2.2.1
DC Motor
The Qube-Servo 3 includes a direct-drive brushed DC motor. The motor specifications are given in
Table 2.2. The motor datasheet is attached alongside this document.
Caution:
Exposed moving parts.
2.2.2
Encoder
The encoders used to measure the angular position of the DC motor and pendulum on the Qube-
Servo 3 are single-ended optical shaft encoders. They output 2048 counts per revolution in
quadrature mode (512 lines per revolution). Digital tachometers are also available for angular speed
in counts/sec on channels 14000 and 14001.
2.2.3
Data Acquisition (DAQ) Device
The Qube-Servo 3 includes an integrated data acquisition device with two 24-bit encoder channels
with quadrature decoding and one analog/PWM output channel. The analog output channel
emulates a linear amplifier by incorporating deadband compensation. The PWM output channel can
be used to directly access the amplifier duty cycle. The DAQ also incorporates a 12-bit ADC which
provides current sense feedback for the motor. The DAQ is used to detect motor stalls and will disable
the amplifier if a prolonged stall is detected when a voltage above 5V is applied. The digital I/O
provides feedback for stall warnings, stall errors and amplifier faults.
2.2.3.1
Deadband Compensation
The Qube-Servo 3 has a default deadband compensation to simplify the learning experience by
compensating for the non-linearities of the Qube-Servo 3 PWM power amplifier.
To change the compensation, when initializing the HIL device add the board/card specific option
deadband_compensation
. For example, to make it 0, set
deadband_compensation=0
to remove all
compensation.
2.2.3.2
PWM Enable
The Qube-Servo 3 driver supports one PWM output channel, which is channel 0. The
pwm_en
board
specific option must be set in order to use PWM output on this card. Set this option to "yes", "y", or "1"
to enable control of the motor using PWM command. When this option is set, the analog output
cannot be used. This will also disable the deadband compensation and ignore any user-specified
deadband compensation value in the board specific options.
2.2.4
Power Amplifier
The Qube-Servo 3 circuit board includes a PWM voltage-controlled power amplifier. Table 2.2 in
section 2.4 describes its specifications.
