From: Jeff Peterson 
Subject: Viper maintenance report.

Azimuth System.

We now have three AZ motors and tachometers working on Viper.

Spare AZ motor (S/N 4) has been assembled, but lacks heater pads.
Bob Pernic suggested Mark Thoma would be able to complete

Assembled spare tach (S/N 4), complete with heater.

Reduced by 1/2 the heat applied to the tachs since there was evidence 
of past overheating.  All four tachs are modified and interchangeable.

Rebuilt AZ tach #1 cable.  Several cables on Viper are in poor condition
and should be rebuilt.

Only two motors are currently driven, since one techron is out for 

There are two spare techrons here, but we didn't get either running. 

The techron that was damaged in shipment failed a bench test.  Both the
overload and over-temp lights lit on powering the amp. It will be
returned to techron for repair, hopefully back at pole for closing.

The new spare techron has a unique power connector, and techron provided a
mate, but we would need to make a patch cable adapting to our standard
twist-lock.  Better, we can open the unit, remove the unique connector and
install a twist-lock. Also the signal input is a "twin-ax" bnc, instead of
a barrier strip. Here again I suggest modifying the unit to match all the
others.  We didn't have time to do this, and lacked the twist-lock
The twist-lock connector we want is recessed, panel mount 20A 3 phase Y 
120/208v 5 wire. It should mate to Pass & Seymour legrand L2120-C.
We should try to buy this from techron to insure compatibility.

Attempted tuning the AZ servo using two amplifiers and immediately
encountered a problem... at low gain the AZ system had a severe bias
toward counterclockwise rotation (looking down).  Traced this problem to
an intermittent short in the tach summing box between the tach and the
interlock circuits.  The problem only occurred when the power amps were
enabled which made it difficult to diagnose.

After fixing that we tuned the servo. The initial settings were P = 0.45,
I = 0.35.  The onset of instability is P = 2.5, I = 1.1.  Left settings at
P = 1.5, I = 0.7. quite stiff.  stable. When the third techron is
installed the settings will need to be reduced to 2/3 of these values.

Didn't get the AZ system to operate under computer control.
Mark Thoma's circuit that allows comsoft to enable/disable
the servos did not respond to command F-10 on comsoft.
Didn't find Marks schematic of this circuit and settled
for generator-driven tests.   

Jacked one wheel to check for bearing wear. Found slight 
friction (normal), no play, no sticky spots. Perfect.  Made no change of 
preload and decided not to open up the bearing for inspection.
These bearings are used on car wheels and often last 200,000 miles,
at high speeds, under much more severe conditions (potholes, dirt, etc.).


Changed the sliders on the coarse actuator to new ones with
steel end-caps and no seals.  Works well, drawing only a few amps.
We have ample spares.

Fast shutdown.

Installed and tested the new fast shutdown system. Trip point is 
adjustable up to 20A.  Worked well, but we only tested for one day,
and didn't use computer control.  Left set at 20A.


control room is clean.  pump room is not.  cleaned out viper spares
cabinet, about 1/2 the contents were obsolete, or were for spirex.


Left sketches of the fast shutdown schematic and tach summing box 
schematic on the control room shelf.


Installed IP phone in Viper control room  
MAPO IP phone                            
MAPO Iridium phone                       
COMMS Iridium phone                      

To Do List.

Add heaters and thermal shutdown to AZ motor S/N 4
Return damaged techron for repair.
Modify spare techron to use standardized connections.
Test AZ system with three techrons.
Repair comsoft F10 control of servos.
Inspect cabling on Viper and rebuild as needed.
Clean pump room.
Move Viper, ACBAR, SPARO cabinets to covered walkway (when ready).
Improve snow covers at AZ axles. (axle and motor are both exposed)
Clear snow under deck below Viper (five feet clearance).
Add heaters to both ball screw nuts.
Organize and inventory spares.

JP 12/04