RA Drive

[Tom Droege <tdroege@veriomail.com>]

I have put together a new RA drive with all the improvements.  I have been 
testing it today.  I just fixed all the little nagging problems.  There is 
now a way to adjust the cable to get the turnbuckle where you want it.

Arne will be pleased to know that the RA limit switch can be moved to 
anywhere along the RA travel where you are willing to drill and tap a 
hole.  The prototype of the day has a position at the east limit and one a 
little west of the center.  We are drawing it up now to send to the 
shop.  I am putting a position for a limit switch at the maximum east 
travel, and at one inch intervals for a total of 7.  One inch is about 5 
degrees.  Guessing, the east limit is at about 20 degrees east.  This will 
allow a limit switch at 20 E to 10 W in 5 degree steps.

If anyone sees a reason for more holes or finer steps, now is the time 
(next 2 hours or so) to get in a request.   Otherwise you can drill a hole 
where you want one.

The new arrangement will allow multiple limit switches.  The limit position 
will depend on the direction of approach to the switch.  So to know the 
position you must always come at it from the same direction.  The flag that 
covers the switch is 2-3 degrees wide.   OK, I could have made it so the 
flag that interrupts the switch is full carriage wide.  Then you could tell 
your absolute position to 5 degrees by which switches were covered.  This 
would be an easy modification for someone with a good machine shop 
available to them.  Or cardboard, glue and patience.

But if several switches are installed, it is not so hard to tell where you 
are.  Home east to any switch.  Then look to see which switch is covered 
when you stop.  There are lots of switch positions provided for in the 
electronics, it is just a question of stringing wire through the telescope 
motion.  I will deliver systems with one switch provided, the most east 
position.  You can request more, but then someone will have to fix up 
software to allow for more than one switch in use.

It will also be possible to move a single switch to different positions 
with about a tenth degree uncertainty after a move.  Possibly less, I have 
not tried it.  This is just my estimate of the uncertainty of positioning a 
switch when moved.

I plan to update ARNE and MICHAEL when I get to it or for whomever pleads 
the best case.  I will just ship out a whole RA drive for 
exchange.  MICHAEL has my prototype of this design, so he has some of the 
improvements.

I also used hose clamps on the motor coupling instead of cable ties, and it 
makes that connection much more reliable.

Now to install it on TOM and see if I can start taking images again.

Progress every day!

Tom Droege