M3 removal gear & a special visitor

Alex O'Donoghue joined us from London for a couple of days to inspect the clean room & conduct Darragh's performance review in person... Dad does indeed seem to be working particularly hard these days.

Craig came up too, bringing along the gear he designed & built for removing M3. That will be needed for the M2 test & also for the M3 test to be done with the big CGH that's on its way - more about That later...

The M3 removal jig involves 4 car jacks & a pair of trolleys that travel on something like a railway track. The trolleys attach to the M3 cell & once secure, the cell will be detached from the rest of the SAC & whisked away to a comfortable new box.

While all that was happening underneath the SAC, the AMNH Faro Arm was attached to the NRS simulator & prepared for setting up a coordinate system & measuring the invar buttons on M2 & M5...

Knowing now that the various encoders need to be made to work during every measurement & that the errors can be averaged out by getting tons of data, using the Faro has become a team sport. 2 to wrangle the beast & 1 to hold down the insert key on the laptop to collect the 1000 readings per point!

It's not right, but it's ok...

We changed our strategy today after yesterday's tests (that involved moving the Faro around & measuring the same points over & over) produced unacceptable results. As a last resort before declaring this arm unusable, we decided to keep the Faro in one place & move the measurement points around to see how that works...

We employed a steel bar with 4 measurement points drilled along its length for this purpose. The bar can be clamped to the Faro test plate in practically any position, allowing the arm to measure the same lengths (between the 4 points on the bar) in a variety of ways. This lets us exercise all the arm's encoders during the measurements, thereby averaging out the encoder errors.

This produced remarkably good results so although the AMNH Faro Arm's out of spec, the mean values obtained from the various sets of 1000-point measurements are in good enough agreement for our purposes. When using the arm in anger we'll need to take 1000-point averages & make sure we exercise the encoders as much as possible.

Grilling the Faro

Today's Heritage Day - a public holiday that's become known as "Braai Day", in celebration of one of SA's favourite culinary traditions. It seems appropriate then that we should be grilling the AMNH Faro Arm, putting it through its paces in order to thoroughly characterise its performance...

An old alignment jig for the primary mirror mounts was converted into a test plate for the Faro.

The plate provides 3 different attachment locations for the Arm & 10 widely spaced points for making measurements. All 10 points were measured for each base position & readings were taken in continuous mode (which produces 1000 data points per measurement) while exercising all the Arm's encoders as much as possible for each point.

This required some rather fancy "langarm" dancing from James & generated over 100,000 data points (including calibration measurements) for us to crunch through & plot up...

Dealing with these volumes of data is time-consuming & can be quite mind-boggling, but we really need to know that this critical tool's working the way we expect & need it to.

Back in Business!

The IQ Team returned to SALT today - prancing through the spring wild flowers with their "new" Faro Arm...

Very special thanks to our SALT Partner Of The Month: The American Museum of Natural History (AMNH) who arranged to lend us their Faro while ours is being resuscitated in Germany. We hope to get the latter back within a couple more weeks, but having a substitute available allows us to get back to work in the meantime :)

Deeply suspicious after our past experiences, this arm's getting a thorough work-out to make sure we know exactly what it's up to...