counterweights and controller

It has been a week since the last post, so here are some of the things that went on.

First, Brian and I are currently the only people here. There are plenty of ethernet connections now.

Brian and I did a measurement of the imbalance with a heavy duty hydraulic scale. We where able to determine that there are 9000 ft-lbs of imbalance, with the CG toward the shields. It turns out that this measurement comes very close to the measurement from the motor current that Sean came up with. I was hoping for better. I think the reason we are off is because of the baffling, it was just heavier that I estimated.

This imbalance is bad for a couple of reasons. First, I talked to the designer of these drives, and he definitely thought that the friction wheel was not designed to hold that kind of imbalance. Secondly, if the system where to fail, it would end up with the boom down, so not very safe.

To fix the counterweight problem, Brian and I decided to go with Steel. This is after we scambled around looking for lead or other solutions. The OVRO staff told us to go with a welder in Bishop, and they will, source, cut, and deliver our counterweights for $2 a pound, which is not bad. The couterweights will show up on Tuesday, then we have to paint them, and then on Thursday we are having a boom truck come out here to install them. This should get us within a few hundred pounds of balance, and then we can add trim weights.

A second problem that developed has to do with the servo. I think that I burned a chip on the AZ motor controller. Mike sent me an accelerometer so that I could look for resconances in the structure. I was slewing the telescope 360 degrees in 90 seconds, then stopping and turning around. After looking at the accerometer data and trying again, I foind that the Baldor controller was complaing of a low DC bus voltage. These things are suppossed to protect themselves from events like this, so I am not sure how this happenned. After talking with Sean, he decided to get a new unit, and will bring it next week. Until then, we have to move the AZ the old fashioned way, by pushing.