15nov04 td4 motor trouble

    Tiedown 4 failed on 12nov04. Breakers cb2,3?? were tripping. It was left in that position till 15nov04 because of an aeronomy run in progress. On 15nov04 the motor power supply was  replaced. The dac signal conditioning board also had some blown chips so it was replaced. After the replacements the following problem was still noticed.

• Command the motors to go to a different position from the off state.
• The power comes on and you can hear the brakes release.
• Td 12 and td8 begin to move but td4 does not move for a few seconds. The motor then jumps to full speed causing an over speed on the amplifier. This causes the amplifier to shut down.

• Top plot: The tiedown position versus time. Each * is one second. The red trace is tiedown 4. All 3 of the tiedowns had been commanded to go from 12 inches to 11.5 inches.  Td12 and td8 started moving at 14 seconds. Td 4 made a small motion at 23 seconds.
• 2nd plot: The velocity feedback is measured by the a/d converter at the input to the amplifier. It is the requested velocity. This is the voltage that is being sent out by the dacs to the amplifier (via the signal conditioning board). You can see that the commanded velocity begins to change for all 3 tiedowns at 13 seconds. Td12 and td8 actually move so the PI loop causes their velocity to then slow down. Td4 never moves so the requested velocity ramps up to the maximum and sits their. The purple line is the digital value sent from the computer to the dac board (it differs in a scaling factor). The dacs are doing what is requested of them. The jump at td8 at 19 seconds is a spike in the data monitoring.
• 3rd plot: This is the speed monitor that the amplifier reads back from the motor. It measures actual motion of the motor. At 13 seconds you see td12 and td4 start moving but td4 remains fixed.  At 23 seconds td4 velocity jumps to the maximum for 1 second then goes back to 0 (because of the over speed condition).
• 4th plot: The motor status as derived by the little star program. All tiedowns go to enabled at 13 seconds (value of 1). At 23 seconds td4 goes to 0 (off).
• 5th plot: The motor torque (current )as read back from the amplifier. The currents increase for td12 and td8 when they start moving. The current for td4 does not increase.

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