Motor test after adjusting td12 curLim,cmdScale

    In dec07 one of the azimuth amplifiers was installed on td12 for testing. This caused problems with td12 stopping.  It turns out that the current limit pot on the amplifier was set too low for the tiedowns. On 28jan08 the current limit and command scale pots were  adjusted. The amplifier pot settings before and after were:

• no current limit..  pot is completely clockwise.
• starting position.. pot is 1.5 turns ccw from no current limit
• after adjustment.. pot is .5 turns ccw from  no current limit.

• Slewing tries to move at the maximum allowed velocity. It does not feedback the position
• Tracking will move at a requested velocity and feedback the position error each 5 millisecs.

• page1:
• position vs time from encoder.
• Tiedown velocity vs time using the encoder position.
• Tiedown tension during the test. The max allowed tension is 120 kips.
• Motor current vs time.
• Page 2:
  
• Requested velocity cmd in d/a cnts. 2048=0vel, 4097 is max.
• DtoA velocity readback. This  is the dtoA voltage output readback before it arrives at the motor input. 0 volts is now zero velocity. There is a scaling (from the a/d readback) in the values.
• Motor rpms measured from the encoder. The most accurate way to read the velocity is from the encoder (the motor has a separate voltage readback proportional to velocity. The gear ratio between the encoder and the motor is 90 with 4096 encoder counts per encoder revolution. The ratio between the encoder and the jack is 10.66.
• Page 3:
• Scale factor between motor rpm's and dacVelCmd is the slope of the motor rpm vs velocity cmd (in dac units). The scale factor depends on:
• DacCmd to DacOuputVoltage
• CmdScale setting at the amplifier.
• Current limit setting in the amp. If the current limit is set too low, then at high dacCmds and hi tensions you should see the velCmd increase while the motor rpm's remains constant. (we don't see this).
• Scale factor between motor rpms and dac velocity feedback. The feedback is read with an a/d before the voltage enters the amp. The scale factor depends on:
• Voltage output by the dac
• Input gain for the a/d
• the cmdScale for the amp.
• Plot discussion:
• td12 with  85 kips of tension is no longer stopping.
  
• the measured max velocity for td4 (.07 in/sec) is less that td12,td8 (.088).
  
• Td 4 has a max velocity of 4000 rpms while td12,8 are going at 4900 (the motor maximum).
• TO DO:
• Calibrate the velocity feedback for all 3 tiedowns. We can then use it to troubleshoot remotely.
• set command velocity to 4095.
• Measure the output voltage on all 3 dacs.
• Measure the velocity feedback. The ratio should be that of the measured voltages. If not adjust the resistor used on the a/d readback.
• Calibrate the dac outputs (using the velocity feedback).
• Set dac cmd to 4096.  Adjust the dac signal conditioning board so that all of the dacs give the same voltage output. You can use a volt meter or the calibrated velocity feedback.
• Calibrate the command scale.
• Measure the motor rpm's vs the dac command. It should get to 4900 rpms when the dac command approaches its maximum value (4095)
• Check the amp current limit.
• Put max tension on a tiedown, move to 20 inches, stop, and then try to start and pull down to 21 inches. make sure there is enough torque.
• Run a tracking pattern between 19 and 21 inches. The tiedown with the high tension should perform the same as the other two.

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