td12 needs large torques to move. Jack to
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.
When foldback and cmdSpdErr happen there is usually a real problem.
The jack is not able to move at the requested speed because too much
torque is required.
Plots were made of the tiedown data from 01mar12 thru 19apr12 to see
if any patterns existed.
- 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
- 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
- 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
- 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
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)
- td12 jack stopped moving with foldback errors (and cmdSpdErr)
- 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
- td 12 jack needs to be replaced.
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