1. Blanco mirror lift upgrade ACTR #480
Tim Abbott & Patricio Schurter
11 May 2015

2. Existing drive configuration

3. Safety factors (for Mayall lift)
Before upgrade:
After upgrade with 50T actuators:

4. Upgraded Mayall Drive
Not installed

5. The Mayall experience
Duff Norton ball screw lead time was 1 year (2x anticipated).
Duff Norton could not do factory load tests.
Manufacturing quality questionable.
Fouling in ball screws required mods.
Tuning of drive was problematic (3 motors)
Tilt encoders and limit switches worry us.
Safety catchers not done (no space)
But it’s done now and works.

6. AAT design Outside vendor: PM Design Group, Victoria Australia
Identified 2 major load cases:
Mirror preload
Mirror removal/installation
Identified 6 concept solutions:
Do nothing
Existing elevator + cable counterweight (Est. US$410k, 2012)
3x 50T actuators (single motor) ($515k)
3x 50T actuators + “redundant load path device” ($610k)
Wire rope winch ($690k)
Load cells on mirror cart
AAT went with (3) + (6), plus load cell in drive base (didn’t work)

7. The AAT experience Ball screws from GROB (Germany)
Very high quality (“compare WWII bomber vs modern Boeing”)
Looked at Duff Norton, decided against them (“hopeless”).
Single motor, direct drive
Slower, but not enough to matter.
Selectable torque – used as safety limiter after drive base load cell “did not work”.
2 brakes on the motor + another on the drive.
Cost more than expected
Bells and whistles don’t work:
Envisaged system to know what is on the elevator & interlock
Collision avoidance system doesn’t work
Sensing device on trolley doesn’t work.
Static load test, 120% load
The system did back drive despite claims that it could not

8. To do next…
Intra-NOAO meeting to discuss detailed pros and cons of each design.
More conversation with AAT
FEA to figure out where bending loads concentrate
Port Mayall and AAT existing load and new design calculations to Blanco
Establish pertinent Chile and OSHA safety codes
Open a conversation with PM Design Group
Can we collaborate on a modified design?
All assembly & installation done by us.
The above require ~2 weeks of Patricio’s time, this month, plus 2 more in June.
Then:
Tim and Pato go to Oz
Visit AAT
There is much to learn besides the mirror lift: they have shutter problems too, can look at their dome drive, aluminizing procedures, etc.
Visit PM Design Group
Negotiate need for PM Design Group engineer to come here?
‘roo hunt, shrimp on barbie, go walkabout in the outback, argue relative merits of Marmite vs Vegemite, “Now this, this is a knife”, whinge, “No worries, mate” etc.