Log of July 2006 events
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Wednesday, July 12, Wednesday, July 19
Meeting scheduled - 1:30 on Wednesday, July 12.
from Dave Bennet to: Jack Grogan, Dick Oswald, Ed Thelen, Pat Connolly, Al Hoagland, Joe Feng
Purpose of the meeting is to talk about overall system layout to incorporate the new servo system that Dick Oswald is designing, and to discuss how we should proceed.
- Due to big doings at the CHM, we found each other in the Oral History Room
- Attending were - Dave Bennet, Jack Grogan, Dick Oswald, Ed Thelen, Al Hoagland, Joe Feng.
- Apparently Pat Connolly had a meeting with his faculty advisor - some thought that an adequate excuse ;-))
Dave Bennet drew the image on the left to focus our attention.
- Jack Grogan noted that there should be hardware protective circuitry, and possibly command verification, in the servo system, such as cutting clutch power if a limit switch is hit. Dick Oswald mentioned that there should maybe a hardware time out function - if the seek is not completed in a generous time, there is likely a fault and servo power should be cut.
- I noticed that the previous meeting (June 20) that considerable focus was on getting a student involved.
- Later in this meeting, it was noted that getting a faculty advisor to monitor student progress at CHM (on a weekly basis) would be a time consuming problem for the faculty advisor.
- Focus shifted to obtaining exIBMers, similar to the success in the IBM 1401 project. Dave Bennet mentioned that he eats lunch most Wednesdays with Herky Hanson. (11:30 - Hi 5 Pizza, Snell and Branham) There seemed general acclaim that Herky was a cheerful talented tinkerer and would be a valuable addition to any team. Three of the people present had worked with Herky, and were delighted that he might be enticed to join.
- There was talk of project organization so that much parallel activity could continue even if someone insisted on taking a vacation. ;-)
- Defined interfaces, test jigs, subsystem test, ... (OK, I added some buzz words, but you know what I mean ;-))
- The current human interface is not very convenient. Adequate to demonstrate that a seek can take place, but requiring a re-compile, re-down-load for each seek. Dick Oswald knows of LabVIEW from National Instrument. (I (Ed Thelen) have a student edition 7.1 and am struggling to learn it. A friend works with LabVIEW at National Instrument.)
- There was discussion of the previous episode of apparent head staying within reading distance of the disk when the "head down" switch was turned off. Head piston? air valve? switch? other?
- The meeting broke up - I think Joe Feng was going to give a RAMAC data demo - I (Ed Thelen) had to split :-((
- Dave Bennet hopefully will enhance these preliminary notes.
Wednesday, July 19
- Ed Thelen came in to do some measurements.
- Noticed the 733 differential amplifier (for amplifing the head read signal) has been removed.
A nice image of the plugs on the RAMAC
The resistance of the air valves is about 1700 ohms +- about 5%
- The electromagnetic drive clutches have
- - about 310 ohms resistance,
- - and 1700 millihenries inductance.
The inductance was measured by a meter loaned to the 1401 project by Grant Saviers.
- Pin outs of RAMAC Connectors shows no tachometer (pin 29) return wire -
- the black wire in the bundle goes to pin 24
- the blue wire in the bundle goes to pin 29
Pin 24 is listed as "Solenoid (3) H Common V + 40 V"
- I am assuming pin 24 is a solenoid ground wire which the students connected to +40 volts for solenoid driving convenience? Could the actual solenoids in the original machine have had their other lead activated to +40 volts by say relays - and wire 24 have been the common solenoid and tachometer ground?
This is feasible as the tachometer has a high output (3.6 volts per 100 RPM), and any IR drop due to solenoid current (25 ma each, with no more than 3 solenoids energized at a time) would be insignificant.
- The top and bottom safety microswitches open when the arm assembly is too high or too low.
- I could not identify arm in/out limit switches - I need some expert guidance.
- I have updated Pin outs of RAMAC Connectors to better identify the labeling of the plugs at each end of the wire bundles, and to identify the sockets/plugs and pins interfacing the student driving board.
- Interesting fact - one revolution of the drive capstan (max 1000 RPM - 60 milliseconds) drives the head from all the way off disk - to innermost track -
If you have comments or suggestions, Send e-mail to Ed Thelen
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