I recently got the Motor DC Trainer (Quanser). They include two different VIs to measure: one measures simultaneously current and speed and the other VI measures only speed. You expect to get the same value regardless the VI. However, when measuring Speed with one or the other you get different values (by a factor of around 3). I review the block diagrams for both VIs and discover that the math is different. One VI (QNET_DCMCT_Speed_Current_Read.vi) does a division by -360/1024, while the other (VI QNET_DCMCT_Speed_Current.vi) doesn't. This division turns the calculations into a difference of a 3 factor. Obviously one is incorrect. My question is which one is the correct?? The trainer has a good manual on how to use the 3 main VIs of the trainer but does not provides any single idea of the hardware specifications.

If you are using the REV 1 motor, the QNET_DCMCT_Speed_Read.vi is the correct sub-VI to use. If you are using the REV 2 motor, the QNET_DCMCT_Speed_Current.vi should be used. See the PDF in the posted link above to identify which motor you have. The QNET DC Motor Trainer has a digital tachometer - it computes the velocity based on the encoder. Because the REV2 motor has less resolution (and the motor sign change), the original TACH calibration gain of 1050 RPM/V has to be multiplied by "-360/1024". The REV1 system encoder has 360 lines/revolution and the REV2 system has an encoder with 1024 lines/revolution. That's where the numbers for that calibration factor comes from. The Speed_Read and Speed_Read_Current VIs should both share the same calibration - Speed_Read.vi did not get updated when REV2 was released. We'll make sure to update this fix in future releases. Hope this clarifies things, Mitch

Academic Hardware Products (myDAQ, myRIO)

NI Elvis II Motor DC Trainer (Quanser)

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Mitch:

thank you so much for your kind assistance on this. Now it is very clear.

BR,

Ivan

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Academic Hardware Products (myDAQ, myRIO)

NI Elvis II Motor DC Trainer (Quanser)

Re: NI Elvis II Motor DC Trainer (Quanser)