Td 12 stopped moving on 18apr12 around 20:00. The error was cmdSpdErr and foldback.

• cmdSpdErr occurs when the motor speed read back from the amplifier differs from the requested speed but a specified number of counts (i think it is currently 300). This could be a a/d input problem (the voltage divider  resistor is wrong) or a real error with the tiedowns not moving as instructed.
• foldBack errors occur when the requested torques are above the allowable maximum for a period of time.

• The first plots shows the td torques and position vs daynumber of year (.pdf):
• The 3 tiedowns are color coded : black td12, red td4, green td8.
• Only data when the tiedowns were moving were used
• Top: motor current vs daynumber.
• You can see that td12 (black) is much larger than the other two td's.
• Bottom: Td position vs daynumber.
• All 3 jacks moved close to the same positions.
• During the nights the jacks were between 14 and 15 inches.
• The second plot shows the motor torque vs the tension on each tiedown (.pdf):
• The force the motor applies is related to the tension in the cable, the direction of motion, and  how fast the tiedown has to move.
• The motor torque is proportional to the force the motor applies.
  
• For the same force on each tiedown (say 30 kips) td12 needs 4 to 10 times as much current as the other two motors.
• This could be a problem with the current readback from the jack
  or it could be a real problem where the friction in the jack motion is much larger than the other 2 tiedowns.
• On 19apr12 while testing the tiedowns, loud noises were coming from td12 jack when when tried to pull down on tiedown (increase the tension in the tiedown cable).
• These loud noises and the large torque needed to pull on the tiedown point to a broken jack (or transmission)

Summary:

• td12 jack stopped moving with foldback errors (and cmdSpdErr) on 18apr12.
• Plotting the motor torque vs tiedown tension showed that td12 needed 4 to 10 times as much torque as the other two tiedowns for the same cable tension.
• This has been occurring at least since 01mar12.
  
• Loud noises were heard in td12 jack when moving it on 19apr12.
  
• There have been intermittent noises from td12 for the last few months.
• td 12 jack needs to be replaced.
  

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