Altitude Drive Box Replacement
Requires at least 2 persons and 4-5 hours.
A. Preparation:
1. Remove railing for Apollo
2. Lower Altitude to 6 deg stop and tie down, push in stop button
3. Power off altitude amplifier in control box under Na2 hatch by turning off utility power strip (beige in color)
4. Align Bridge crane with altitude drive disc, install long strap (12ft) to hook and lower pendent to Obs level
5. Disconnect 2 electrical plugs on back of motor
6. Install 3/8ñ shoulder eye bolt to drive box above motor coupling
7. Attach crane via long strap and shackle to eye bolt
Figure 1. Rigged for removal
Fig 2. Strap running along drive disc
B. Removal
1. Back off encoder pre-load 2 turns
2. Remove encoder by removing 4 bolts. Holding mount to drive mounting block NOTE: encoder and mount are heavy (40 lbs) and must be supported when being removed and lowered to the ground. Do not allow the encoder or mount to impact the drive disc during removal. Do not disconnect the electrical connections for the encoder.
3. Loosen cam followers on right side of drive box
4. Remove 2 bolts attaching drive box to flexure. Keep spherical washers (4 sets) in proper order. Note; the 2 sets between the mount and the drive box are easiest to remove by raising the drive box with the crane 1/4ñ
Fig 3. Flexure mounting bolts
Fig 4 Bolts with spherical washers
5. Continue to raise drive box along drive disc until horizontal. Note: watch the hook and adjust crane fore/aft position to avoid hook hitting the secondary exchange grating or railing.
Fig 5. Lifting drive box
6. Install 2 pieces of cardboard between the drive box edge and the drive disc so that the box will not contact the disc during removal.
7. Once in position, loosen the preload and remove the rollers that is supporting the drive box on the disc. Note: This should be down on both sides simultaneously.
8. While guiding drive box to avoid swinging and hitting the disc, remove roller T-brackets that the rollers were attached to.
9. Allow drive box to swing clear of disc and lower to cart on floor.
C. Installation Preparation
1. Clean new drive box wheels
2. Replace side rollers and cam followers if necessary
3. Clean encoder wheel
4. Transfer Eyebolt and crane hook up
5. Wipe down drive disc
D. Installation
1. Raise drive box and carefully mate with disc and install T-Brackets and pre-load rollers. Adjust preload rollers approximately 1/2 way
2. Lower drive box in place with crane, Install spherical washers and 2 retaining bolts and tighten snug.
3. Disconnect from crane
4. Tighten roller preload by until Bellville washers flatten out . then back off 1/2 turn. Note: should be done on both sides simultaneously
5. Tighten 2 bolts holding box onto flexure .
6. Align cam followers on side rollers such that they just touch the disc and tighten.
7. Reinstall encoder noting precautions during removal.
Fig 6. Reassembled
E. Setup
1. Install hand crank in place of motor.
2. Untie telescope and raise to approximately 10 deg
3. Rotate the telescope up and down by hand and watch for slippage. If slippage is present (likely) adjust preloads internal to drive box until slippage is gone.
4. Adjust encoder preload by tightening the preload screw until Bellville washers are fully compressed (gets hard to turn) and backing off 1/2 turn.
Fig 7. Adjusting box preload
5. Install motor and connect ions
6. Power up amplifier and set engineering stop button switch to bypass.
F. Checkout
1. Open mirror covers
2. In terminal connection with TCC ,
telrun: ðdisable proc statusñ
exit
host tcc_alt: STATUS
INIT
3. run axis up and down by starting slow ð10 MC.GOñ
and progressing to 20, 50 100,500 then repeat in ï direction
NOTE: telescope may think it is below or above software limits due to encoder R&R. If that happens then a ðREMAPñ may be necessary see below. The position reported will almost certainly not match the actual position so monitor the reported position during this checkout.
During operational checks listen and watch for odd noises, slippage or other signs that something in the new drive box may not be right.
4. After operational checks run a ðRemapñ being certain to manually trip and release the lower limit switch rapidly as the switch approaches the flag. (necessary to avoid oscillation caused by a firmware bug)
Following ðREMAPñ type MS.MAP.DUMP in the host session.
Copy data from this list to the ðinit_alt.dat ð file in the tcc (tdat directory) by deleting the map data in that file and replacing it with the new data.
Also run a ðMC.VEL.OUT.SCALE F@ F.ñ in the host session and copy that number into the same ð init_alt.datñ file by replacing the number in that file with the new one.
5. Install stop button
6. Return engineering stop switch to normal
G. Further checkout
1. Run test slews while observing Dataq for anomalies
2. Run vel scale routine in up and down directions, average and update init file
3. Checkout tracking on the sky and adjust PID parameters as necessary.