Motor Lab Notebook

Motor Lab Experimental Series FSA001A

Optimal waveform, frequency and counter - rotation mode tests

 A trial and error procedure was performed to find the optimal frequency and phasing of the Channel 1 and Channel 2 waveforms to achieve smooth rotation of the compass needle in both deflection yokes. It was also desired that the needle rotation direction (Clockwise or Counterclockwise) reverse when the compass was taken from one yoke and placed in the other. After several modes were checked, the following waveform parameters seemed to produce the best result:

                              Ch.1                              Ch.2

Wave Function       Sine                                Sine

Frequency              80 hz                               80 hz

Phase                      0 deg.                             90 deg.

Modulation Depth    90 %                              90 %

Period                      0.12 sec                         0.12 sec

Phase                       0 deg.                            180

The waveforms' appearance on the DSO output monitor:

 After this optimal result was achieved, the rotation directions were checked.

The system as diagrammed in the schematic on page one produced rotation in both yokes in the clockwise direction. The connections to the horizontal windings on one yoke were then reversed, and a counter rotating effect was observed with the application of the same power signals. A digital movie (AVI) recording was made, however the rotation speed made it impossible to determine by viewing the recording which directions the compass needle was actually going, due to shutter speed limitations of the recording unit (a digital camera in movie mode). This recording was discarded and a second recording performed, this time being careful to capture the decelleration of the needle as it was removed by hand from each of the yoke fields.

The resulting AVI can be viewed by clicking here.   

Jim Ostrowski  3/05/05

Field Vector Test 3/08/05

The two deflection yokes were hardwired to each other and connected to the power amplifiers and the above signal was applied to produce the counter - rotating field. A computer monitor was procured and it's original yoke was removed and replaced by the smaller of the two test yokes as shown below:


The signal was applied and the resulting vector plot trace (lissajous figure) was digitally recorded. The effect of this recording was to actually shutter - strobe the moving trace on the screen of the monitor. The resulting AVI was uploaded to the site and can be viewed by clicking here. The video frame rate of the recording device (a digital camera in movie mode) strobes the action to show an apparent trace velocity by about 1/2 that which can be observed visually 

Jim O. 3/8/05

Field Balance Test 3/09/05

The above setup was tried again to see if the field vectors could be equalized by rotating the balance control on the stereo amplifier shown in the diagram on page 1.

It was found that rotating the balance control would indeed alter and adjust the relative amplitudes of the field's X-Y vectors. A video of this effect was recorded and uploaded to the site, which can be viewed by clicking here.

The signal generator was then programmed to produce the quadrature (sine-cosine) signal depicted on page 1. The signal generator was adjusted to produce as nearly perfect circle on the monitor screen as could be judged by eye. An attempt was made to photograph the effect, however the camera malfunctioned and the cause was determined to be a low  voltage condition of the camera batteries. Fresh batteries were not immediately available.

Oscilloscope measurements for the relative signal amplitudes of ch1 and ch2 were taken and the following data points were recorded by hand on notebook paper:

All voltages VACp-p

Medium sized circle:

Y1:  1.34                       Y2  0.552

Large circle:

Y1  2.08                        Y2  0.848

Small circle:    

Y1  0.492                      Y2  0.200

Very large circle               

Y1  4.36                        Y2  1.70

A linear fit statistical analysis (GWBasic) program was run and the above data was inserted. The program outputs the sum of the deviations squared and a linear fit equation in the form of Y = Mx + B 

The result was the program found that the sum of the deviations squared was 0 and the fit equation as Y = (0.386X) + 0.027

Which is to say that in order to make an equalized circular field vector of any arbitrary diameter the balance control of the stereo amplifier should be adjusted so that the Channel 1 Peak to Peak amplitude = (0.386 Channel 2) + 0.27  

Jim Ostrowski, 03/09/05


Fresh batteries were obtained for the camera, and the experimental arrangement as described above was powered up and adjusted to produce the circular rotating field, and a photo was taken of the result on the monitor screen as reflected off the lab utility (plastic shatter-proof) mirror.

 Jim O, 03/10/05