ROTSE-III hardware manual

Checklist of known problems, and what you should do to protect your mount/telescope

1. A drive motor can overheat due to excessive current over a prolonged period of time (>30 minutes?). The motor will partially demagnetise due to the temperature, and will therefore have reduced performance from then on, making it more likely to overheat in the future. Solution: install a thermostatic cutout switch on the motor body; ensure I2t (current-squared times time, i.e., heating) protection is enabled in the mount software; check the balance of the telescope, and look for cable snags.
2. The drive capstans can be shredded, and the capstan then grinds into the drive wheel. Solution: install Andre's protection widgets, or similar devices, on both RA and DEC axes; replace the capstans; adjust the preload and servo coefficients appropriately; repair the damaged metal surfaces with gentle application of, e.g., Scotch-Brite (take great care not to damage the encoder tapes). See also this additional information.
3. Misshapen images out of focus. Solution: consider reducing the tension on the primary mirror retaining screws. Other possibilities are wind vibration, servo oscillation or collimation errors.
   
4. A "thump" is heard as the mount slews. Solution: it is possible that the RA and/or Dec axes are loose, consider adjusting the preloads.
5. The mount oscillates at low frequencies, or with an audible whine. Solution: the servo coefficients may need adjusting; the drive capstans may be worn; the capstan preloads may need adjusting.
6. The mount oscillates when homing at the home limit switch. Solution: balance the telescope so that it is slightly biased towards the home limit.
   
7. The Renishaw encoder shows orange or red on its status LEDs for part or all of the sky, possibly leading to a position error being flagged by the mount computer. Solution: adjust the encoder position; clean the encoder tape; inspect the RA/Dec axes for loseness.

ROTSE-IIIa cable routing

Oscillation when homing the telescope

Adjusting the drive capstan preloads

Possible causes for shredding of the RA and Dec drive capstans

• The mount computer is running, but the servo software is not running.
• The brakes are applied.
• Excessive current to the motor, causing slipping.
• The capstan preload may be low enough that the drive slips under the steady application of torque. Once large-scale slipping starts, the drive can shred the capstans in a matter of seconds.
  
• Violent oscillation of the capstan due to inappropriate servo coefficients, or a gradual change in the drive characteristics (e.g., once the capstans wear, the rate of wear is likely to increase).

Preventing damage of the drive following capstan wear

Setting the mount servo coefficients: Kp, Ki, Kd

1. Note the existing parameters (Kp, Ki, Kd) so that you can restore them if needed.
2. Put 2 and 0.4 in the f and z box respectively in the "Calculate Gains from Break Frequency and Damping" box and click the calculate button.
3. Copy the resulting Kd and Ki value to the servo parameters for the axis of concern.
4. Lower Kp for that axis to maybe half of its current value.
5. With the servo running (axis in the "Stop" state, probably), raise Kp as described previously.  That is, perturb the axis while raising Kp until the servo oscillates and then lower Kp until the oscillation stops.
   

1. Lower the Kp gain by 60%.   Push on the RA axis with your hand and watch the resposne.  The servo should still be stable.  The axis may have a sluggish response and recover with a bit of overshoot.  This is normal.
2. Start raising the gain with the little up arrow at the right side of the Kp box.  The axis's response to a push will become faster and the overshoot will decrease.
3. Keep raising the gain and listen/feel for an oscillation to start as you keep perturbing the axis with your hand.
4. Once you get an oscillation, quit pushing on the axis and start lowering the gain by clicking on teh down arrow until the oscillation stops by itself.  That's the right place to leave the gain.

• If the capstan slips when you push on the axis, tighten the drive preload.
• If the Kp gain is too low, the axis will oscillate with a low (sub-sonic) frequency.
• If the Kp gain is too high, the axis will oscillate with a high (audible) frequency.
• There's usually no need to fiddle with Ki or Kd.  They set the position of a couple poles in the transfer function, and those shouldn't need changing.  The same goes for the filter coefficients, only more so.
  

Anti-slip and anti-oscillation software

Slipping

Oscillation

Servo.ini files

Measured axis torques

The meaning of the GUI voltage reading

Motor specifications

Mount limit switches

Renishaw encoder

Right ascension bearing adjustment

Declination bearing adjustment

1. Loosen the non-drive side a bit.  Two or three turns on the nut should suffice.
2. Tighten the drive side nut until you flatten the preloading wave spring. You'll feel the tightening torque increase suddenly when this happens.
3. Back the drive side nut off about 1/8 turn.
4. Tighten the non-drive side nut until the wave springs are flattened. This may take considerably more torque that for the drive side since the preload on this side is larger.
5. Back off the non-drive side nut about 1/8 turn.
   

Motor protection

Thermostatic protection of the servo motors

Primary mirror cell adjustments

Metric/imperial?

Adjusting the secondary support vanes

1. Loosen the both ends of the two vanes whose alignments do not pass through the center of the secondary assembly.  That is, there is one vane that is strictly radial and two other that are a bit off of radial. So, loosen the both ends of the two non-radial vanes.
2. For each of those two vanes, slide the end nearest the secondary cylinder in a direction tangential to the cylinder.  There is a bit of clearance in the screw holes that will allow this.  Q: Which direction to slide them (clockwise or counter-clockwise)?  A: In the direction that would tend to pull the vane away from the outer barrel.
3. Tighten the screws that attach the vanes to the secondary cylinder.
4. Tighten the screws that attach the vanes to the outer barrel.  This should tension the vanes.
   

Collimation of the primary mirror and optics tower

Mount the mirror cell on a dividing head from a milling machine (see the image below). The dividing head we used had a central hole which enabled us to inject a laser beam via a 45 degree mirror. We used a portable hand-drill to assist with rotating the dividing head. The next task is to align the parabolic surface of the primary mirror as exactly as possible with the rotation axis of the dividing head. This can take a couple of hours of trial and error with the crude setup we used. Sheets of paper were placed under the mirror cell in order to make fine adjustments to the tilt. We bounced a laser beam off the mirror surface and looked at the reflection on the wall of the room, several metres from the mirror. When the beam does not move when the dividing head is rotated, the mirror is perfectly aligned. We were successful in aligning the tilt to < 1 arcminute, and the centering to better than 0.2mm. The optical access of the ROTSE-IIIa mirror is certainly within 0.5mm of the physical centre as defined by the edges of the mirror.

Enclosure

Vaisala humidity sensor

I/O box

Camera problems

Focus motor

It may be necessary to lubricate the drive screw after approximately 500 hours of continuous use. A lint free wipe should be used if removing spent or excess lubricant from the drive screw. A suitable lubricant can be provided by Newport upon request. (Newport part number CMA-LUBE).

Polyurethane capstans

We have 4-pcs 65-70 black and 4-pcs 75-80 blue. Both are high strength polyurethane poly-ether base. Purchased from metalrubber.earthlink.net in March 2005.

Camera firmware

Photos of CCD boards

Click on the photos for the full resolution images.

Component view: timing board at the top, utility board at the bottom.

Solder side view: timing board at the top, utility board at the bottom.

Component view: clock driver board at the top, video board at the bottom.

Solder-side view: clock driver board at the top, video board at the bottom.

Camera oscilloscope traces

SYR     00 53 59 52 0000 0000 0101 0011 0101 1001 0101 0010
DON     00 44 4F 4E 0000 0000 0100 0100 0100 1111 0100 1110
ERR     00 45 52 52 0000 0000 0100 0101 0101 0010 0101 0010
RDR     00 52 44 52 0000 0000 0101 0010 0100 0100 0101 0010
TIMEOUT 54 4F 55 54 0101 0100 0100 1111 0101 0101 0101 0100

Mount computer

Analog, board 1

Encoder Card

DIO Card, board 0

Quick guide to rush

While not hardware as such, I'm including here a quick quide to some aspects of rush, the Bourne-like shell that ROTSE uses.

rush is based on rc, an implementation of the Plan 9 shell for UNIX. Authors are Byron Rakitzis and Tom Duff. See here for documentation.

Here are some examples of rush syntax:

rhelp # for help on ROTSE specific commands
path=($path /somewhere/else)
echo $path
lastFile=`{ls -t|head -1}
{sleep 60; echo Both commands run in the background}&
for(i in *.c){ls $i}
if(test -f /tmp/junk) echo /tmp/junk exists
while (){echo loop forever; sleep 10}
fn go { echo this is a function called go }
fn go # this deletes the function called go

rush reads the file ~/.rcrc at startup.

Processes that you start in rush are run as root.

Collimation of the secondary mirror

The secondary is flat, so only a tilt adjustment is necessary.

To assist with collimation, it is helpful to have an easy way to take and display an image on the rotse computer. Here is one technique:

1. Make sure that ds9, xpans, and xpaset are installed.
2. Login as observer.
3. Edit the ~/.rcrc file so that the path to ds9, xpans, and xpaset is included in the command search path.
4. Add the following functions to .rcrc:

   fn minit {
   
   # This function performs the initial setup, it should be
   # run immediately after starting rush.
   
     rinit
     rmode manual
     pgrep -f xpans > /dev/null || xpans -p 14285 &
     pgrep -f ds9 > /dev/null || ds9 &
   }
   
   fn mdisp {
   
   # Displays the most recent "junk" fits file.
   
     f=`{ls -t /rotse/data/3a1/*_junk_*.fit | head -1}
     xpaset -p ds9 file $f
   }
   
   fn mgo {
   
   # Takes a 10 second exposure, and displays it.
   
     rexpose -w -t 10 -n junk
     sleep 3
     mdisp
   }
   
   

5. Start up a couple of xterms as user observer. Run "rmonitor" in one of them. Start the rotse system with "killrotse -nob; killrotse -nob -dam; allrotse.pl". Wait until the clam is open and the mount is synced and has moved to the zenith.
6. Start "rush". Type "minit" to initialise. A ds9 window should open up.
7. Type "mgo" to expose for 10 seconds and display the result. Sometimes the most recent image isn't displayed - try "mdisp" to fix this. You might like to use FRAME, NEW in ds9 to put new images into another FRAME for comparison.
8. Focus using, e.g., "fmove -r 3.65". Positions are absolute and in millimetres, although the documentation says relative in microns.
9. Offset the focus by -0.65mm. This should give nice donuts as per the image below.
10. Position the telescope for convenient access to the secondary mirror micrometers. E.g., "rmove -w -r 5 0 0 -d -80 0 0", if the LST is "5 0 0" and you are at Siding Spring.
11. Call the lower left micrometer A, and the lower right one B.
12. Turning A clockwise moves the "sweet spot" (where the donuts are perfect annuli) on the CCD roughly diagonally from top right to bottom left. Turning B clockwise moves the sweet spot roughly horizontally from left to right. 1/16 of a turn is enough to move the spot by about 0.5 of the width of the CCD.
13. Iterate until the sweet spot is in the centre of the CCD, as per the following image: (click on the image for the full-resolution view)
    
    Note how the hollows in the centres of the stars all point towards the centre of the CCD. The final adjustments are perhaps 5 degrees of rotation of the micrometers.

1. After you aligned the mirror and find a reasonable good focus position, you need to put that position into the focus model file.
2. First of all, you should delete the /rotse/data/pipeline/prod/focus_update.dat, which is a small adjustment from mini-focus run. Run "rhup schierd", so the original focus model is in use.
3. According to /rotse/run/etc/schierd.conf on 3a, the current focus model file is /rotse/run/etc/focusmod_060726.dat. You may copy this into a new file, and modify the entry in schierd.conf. Because we are not changing the focus model, the only number has to be changed is the constant term, which is now 3.64202. The trick is to find out the offset between the current model and the new good focus, and add the offset to the current constant. Say, for a certain pointing, the focus model calculate 3.5, and you find it to be 3.7, then you should put 3.64+0.2=3.84 as the constant. To get what focus the current model gives, just point with "rmove -r ra -d dec" in rush, while "rmove -r ra -d dec -n" will just move the mount but NOT the focus.
4. After you've changed the focus model file, "rhup schierd" again. Then you may point again with "rmove -r ra -d dec" to see if the focus comes out good. It just needs to be close enough to the best focus, and mini-focus runs will take care of the fine tuning.

Replacement of the Dec encoder tape

Most of the following images expand if clicked on.

1. Obtain a new piece of encoder tape, and borrow (if at all possible) an encoder tape applicator (see image below). Cut the tape to length with the supplied shears.
   
2. Take off a side panel of the telescope and release the focus cable from the Newport controller box.
   
3. Remove the top half of the telescope. It weighs perhaps 12kg, and is an awkward, but possible, lift by one person. There aren't any alignment pins, just unscrew the bolts and lift off, being careful to clear the central optics tower. We lowered the tube section over the side of the enclosure, but it is also possible to lower it inside the enclosure.
   
4. Attach weights to the telescope so that it is counterbalanced, and can rotate freely through 360 degrees in declination. After this image was taken, the optics were cleaned, and they came up perfectly.
   
5. Remove the old tape by peeling it off, scraping the residual glue with a sharp knife, and using a solvent (e.g., white gas, shellite, Coleman fuel) to clean the disk. Then give the surface and the surrounding area a thorough polish with 400 grade "wet and dry". Finish with a careful clean with methylated spirits.
   
6. Read the applicator instructions thoroughly. Attach the applicator device to the encoder mount. You will need to use the left-hand adaptor plate.
   
7. The following photo shows the applicator guide in position, with the new tape ready to apply. Note that there is very little leeway, and you have to be careful not to bend the tape through too small a radius of curvature. Attach the tape to the disk when the telescope is pointing directly at the north pole (or south pole for Northern Hemisphere ROTSE's) - this is a place that the telescope can never point to once the top half is reattached. Carefully rotate the telescope through 360 degrees, slowly, and in one direction only. After all the tape is on, remove the applicator and use a lint-free cloth and firm finger pressure to securely attach the tape from the outside to each end.
   
8. Collimate the secondary.

Vaisalla precipitation detector

Odds and ends for ROTSE-IIIa

Shipping address for data disks to Michigan

cam3a computer