Electronic Design

Bob's Mailbox

Dear Bob:
Re: "What's All This Motorcycling Stuff, Anyhow?" (Electronic Design, Feb. 9, 1998, p. 141). I just ran across it and I have a theory for why the front brakes on bikes would be controlled by the left hand. Because most people are dominant with their right hand, they would squeeze harder with that hand, particularly under duress. When you slam on the front brakes, you're more likely to flip your bike. Therefore, they put the front brake on the left, the weaker side for most people.

Besides, you want the back brake on the right so that you can really clamp down on the brake when you want to skid out and leave black/blue marks up and down your parents' driveway. (I do that in low gear! /rap)
Adam J. Tolman
via e-mail

My right hand is definitely stronger than my left hand, and I can use it to hold on the front brakes at the desired level and servo the rear wheel just about on, or just barely off, the ground. You can't slow down any faster than that. My left hand isn't strong enough to do that with ease. So, the first thing I did when I bought my new mountain bike was to have the bike shop swap the brake levers and their cables. Now, my right hand works the front brakes—as all imported bikes used to 30, 40, and 50 years ago.—RAP

Hello Bob:
A few remarks on knots (Electronic Design, March 5, p. 142): The square knot isn't intended to be used to tie a rope to something, nor to tie two ropes together, as you imply in your article. The square knot, also called the reef knot in sailing, is used for lashing something to its place, like a sail to its boom (that's reefing), or like tying your laces. It should never be in a situation where it can be juggled around by wind, water, or whatnot, as it will slip. (Can you name a knot that will not slip in this situation? Can you name any knot better than a square knot with two half-hitches, on each tail end, for this situation? Do you think a sheet bend is much better? You still have to put the half-hitches after the sheet bend. /rap)

As for the bowline, your drawing represents a left-hand bowline, which is insecure in comparison to the normal bowline. (Yes, I have heard that's called a Dutch bowline. My goof. /rap) The bowline's main characteristic (other than the difficulty to get it right for future sailors) is an extremely reliable hold under all conditions, and yet it's so easy to untie. (I don't find it terribly easy to untie. /rap) As for the granny knot, you correctly state that it's downright dangerous.

Knots, like most things in life, must stay simple. Adding half-hitches here and there messes them up and increases the difficulty of untying them. (Yeah, but you still have to name a knot that's better than my mediocre square knot with two half-hitches. /rap) And believe me, if tying a reliable knot is of the utmost importance, being able to untie a knot also can be a lifesaver!
Adrian Corfield
via e-mail

That's true. I'll cover this in Part II of Knot Stuff.—RAP

Hi Bob:
The e-mail that you received from Dan Slaughter about the eddy brake (Electronic Design, June 4, p. 113) reminded me of a demonstration on this principle in physics class during my undergrad days. The setup was an aluminum sector that was swinging back and forth through the gap of an electromagnet. Then the professor energized the electromagnet, and the piece of aluminum seemed to stop moving instantaneously! (Actually, it should slow down a lot. But it shouldn't necessarily stop instantly—not if it's at the peak of the swing. /rap) It was pretty amazing!

On a completely different note, with the energy crunch we're having in California, have you noticed LED-based traffic lights replacing incandescents up there in the Bay Area? We're seeing quite a few here in Southern Cal. First it was a few red lights, then green ones here and there, and now even the yellow (amber, as some call them) are showing up all over the streets. Sounds like a great idea to me. The efficiency has to be much, much greater, and they probably last almost forever. Even if a few LEDs burn out, it's still functional. (It will be interesting to see the pattern if one LED goes bad! /rap)
Jim Ford
via e-mail

In Sunnyvale, the red lights have been changed over to LEDs for a couple of years. Plus, when the light turns red, it blinks red for about 1/4 second with increased intensity. Then it goes out for 1/4 second, and then comes on and stays on at red. That blink is a great attention getter!—RAP

Dear Bob:
Our agency coordinator remembers a piece of test equipment that he used at UL called a "Seely" box. It allowed the user to measure changes in coil resistance in a solenoid, or motor, without the need to remove the ac source. The resistance, he says, was measured with a bridge. The box was filled with capacitors. There was a two-pole switch, for "measure" and "run," but the device still worked while the measurement was taken. How do you think it worked?
Bill Shaw
via e-mail

Bill, I have no idea. I don't think that you gave me enough information to tell. Perhaps some of our readers can shed some light on it.—RAP

All for now. / Comments invited!
RAP / Robert A. Pease / Engineer
[email protected]—or:

Mail Stop D2597A
National Semiconductor
P.O. Box 58090
Santa Clara, CA 95052-8090

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