Motorstep_8.2.vi Operation
The current “Motorstep_8.2.vi” uses different control values than the old version “Motorstep” for the input to the DC motor. These
control values are given along the left-hand side of the front panel. They are:
Signal Type: allows selection of different waveform variations to the input applied to the motor “Square Wave “ and “Sine Wave” are
the most frequently used. “Square Wave” generates a sequence of pulse variations while “Sine Wave” generates a sequence of
sinusoidal variations. In the display above, a “Square Wave” Signal was selected to subject the motor to a series of step functions.
Amplitude (Volts): sets the amplitude of the waveform. The peak-to-peak variation is twice the amplitude. The square wave above has a peak to
peak variation of 2 volts since the waveform amplitude is 1 volt.
Offset (volts): sets the offset of the mean input to the motor. In the above display, the mean value or “offset” is three volts. The input to the
motor is a square wave signal of 1 volt amplitude with a 1 volt offset
Period (sec): sets the period of the input waveform. Period is 1/frequency and frequency is 1/period. The input period selected above is 10
seconds yielding a frequency of 1/10 = 0.1 cycles per second.
Periods/plot: sets the number of waveform periods to display per plot. This allows display of repetitive in inputs. Two periods are displayed
above.
Some example input conditions:
A constant input (frequency = 0) to the motor at 4 volts:
Signal type: Square Wave (any will do)
Amplitude (volts): 0 (we want no periodic variation so set the amplitude to zero)
Offset (volts): 4 (the offset is a constant value so we set its amplitude here)
Period (sec): 10 (sets the width of the plot on the “Motorstep 8.2” window)
Period/plot: 1 (one period is 10 seconds, 2 periods is 20 seconds, etc of plot width)
Drive change frequency = 1Hz
Mean drive = 0V
Drive variation = 0.5V
Signal type: Square Wave (we want a series of long square waves, each long enough for the motor to settle fully to a new equilibrium
value)
Amplitude (volts): 0.5 (we want no periodic variation so set the amplitude to zero)
Offset (volts): 0 (the offset is a constant value so we set its amplitude here)
Period (sec): 1/1 = 1 sec
Period/plot: 2 (one period is a 1 second plot, 2 = 2 second plot, etc.)
The variation is a little small, the motor is moving to slowly for a good step response.
Try a mean drive of 2 volts… This reduces the “static Coulomb friction” noise on the measurement
What’s my trick to set the scales on the plot – Just select the “min” or “max” value on an axis and type in the value you want.