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.
This occurred more than once. The plots
show one of these occurrences:
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.
It is not clear why this is happening. It could be that
the brakes are not releasing properly (but you can hear the brake relay
change way before the overspeed condition. This problem occurred at different
positions of the jack so it is probably not a bad spot in the jack.
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.
On the 16th we switched little stars, dac board
to not avail. We had trouble with the little stars keeping the configuration
parameters in eeprom when we cycled the little star power. After lunch
some of the breakers were tripped again. Luis had to disconnect the box
fan to get them to not trip. After that he installed another little star
and everything worked (at least up till now...). So it was some kind of
short in the system ???