Dear Bob:
Re: "What's All This Knot Stuff, Anyhow? (Part II)" (Electronic Design, Dec. 3, 2001, p. 88). Bob, referring to your figure, segments E and I are hypotenuses of triangles, and, therefore, longer than corresponding sides C and G. As you hike and things wiggle around, what's to keep the entire lashing from migrating to the left, so that the hypotenuses become parallel to the sides, and the lashing becomes slack? One possible fix would be to loop segment G around the right-side rail.
Steve Troy
via e-mail
Hi, Steve. Technically, you are right. If I had to lug a set of oiled, polished, shiny, smooth aluminum cylinders, the rope would tend to slide, and I'd have to hook loop G around the side rail. I might even have to add some horizontal lacing and bracing. But that's not a problem because I rarely carry such slippery objects—just a tent and a sleeping bag.—RAP
Dear Bob:
I have enjoyed your many columns over the years. Most recently, "What's All This Analog Stuff, Anyhow? (Part 1)" (Electronic Design, Jan. 7, p. 160) brought back remembrances and nostalgia. Few people know that the lunar roving vehicles were General Motors' electric cars. The mobility (motors and drives), suspension, control, and steering systems were developed at Delco in Goleta, Calif., where I spent 36 years as a practicing electrical engineer and member of the technical staff before I retired two years ago.
There were 2-hp dc electric motors in each of the four wheel hubs. Harmonic drives coupled the motor output to the wheels (hermetic). PWM control was used. Westinghouse D60-T transistors were the switches. These 200-A transistors only handled a few amperes. The large transistors provided 50-mV saturation voltages at the low motor currents (efficiency). The overall drive efficiency was about 96%. (Yeah, that's pretty good. /rap) Nickel-silver secondary batteries provided the power.
Cooling happened through the melting of wax (latent-heat-of-fusion). The lunar rovers could run for two hours before all of the wax melted. Eight hours of resting were needed to radiate the stored heat and solidify the wax. (I bet if you parked it in the SHADE, the motors' wax would cool off a lot faster. But that might not be so good for the BATTERIES. They might lose potency when cold. Were the batteries recharged between outings? /rap) [Yes.]
The mobility dynamics and suspension performance were modeled on an EAI 231-R vacuum tube ±100-V analog computer by yours truly. Each morning, the technician (Harold Landrum) would partly fill up a waste basket with tubes that were removed from the computer and replaced with new ones.
Bruce Murdock
via e-mail
I'm not too familiar with the EAI computers or operational amplifiers. I think that the Philbrick computers, using K2-Ws, K2-Ps, and K2-XAs, in K5-Us, K5-Ms, etc., ran pretty well and didn't need to be retubed more often than two or three times per year. But I really don't know how much maintenance, checking, recalibration, and troubleshooting they needed between one evening's run and the next. I never saw baskets full of tired triodes, though. Thanks for telling about the "good old days," and about electric vehicles that worked well.
P.S. I designed the Lunar Seismic pre-amp op amps, the Amelco 2401BG (one day on a coffee break). They ran for years and years up there—much longer than expected.—RAP
Dear Bob:
I enjoy your work in Electronic Design. I found out today from your Jan. 7 column that you worked for Philbrick in the '60s. I too was much younger then! (Ha! That's barely 40 years! /rap)
I have a favorite book from that period, published by Philbrick in about 1968, titled Application Manual for Operational Amplifiers, A Library of Practical Feedback Circuits. I can't tell you how many times over the years I have picked up that book to recenter an idea that I might be working on. (We agree. It's a very good book—quite useful. /rap)
The reading was such a pleasure in its composition and practical approaches. I know that it was a treasure to many others besides myself. The style re-minds me of your work today; did you contribute to it as well?
Craig Journey
via e-mail
The style was 60% from George Philbrick; 10% from Bruce Seddon and Pete Hansen; 18% from Dan Sheingold; and I contributed 1% or 2% of the technical stuff, but not much of the style. As you can see, though, I learned a lot from it. But George taught by making wise statements. On a good day, I teach by asking questions.—RAP
Bob:
I'm one of those old analog guys (with the beard also), trying to find a schematic of a Rohm pre-amp, part BA301. I can't find the darned thing anywhere (probably due to my reduced brain proficiency in using this Internet search stuff). Do you have any info?
Barry L Smith
via e-mail
Barry, I never heard of any Rohm linear parts. I would try www.dogpile.com, www.altavista.com, or www.google.com. (Actually, we found this at www.yahoo.com.)—RAP
All for now. / Comments invited!
RAP / Robert A. Pease / Engineer
rap@galaxy.nsc.com—or:
Mail Stop D2597A
National Semiconductor
P.O. Box 58090
Santa Clara, CA 95052-8090
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