[CW] On Dot Springs and Dot Stabilizers in Semi-Automatic Keys

[D.J.J. Ring, Jr.]

Shamelessly lifted from the SKCC group in an enlightening discussion.

Rich NE1EE
5:32pm   #131825

On 2020-09-29 14:53:-0700, Chris NW6V wrote:

Here's a link to a youtube video of my 1937 MAC "Property of" bug,
equipped with a W0EB dit stabilizer.
I videoed operation - sending "Ss" with the dit stabilizer disabled,
very lightly connected, and over tightened.
https://youtu.be/2fkZAgDhscQ
73 Chris NW6V

I like the details in this series. I tend toward the scientific, anyway.
Thanks for posting.
It was interesting to see the differences twixt spring contact landing
on dit screw as the damping changed.



--
72/73 de Rich NE1EE
On the banks of the Piscataqua

==================================

John KC4LZN
Chris,

Very impressive to see the differences side by side. Shows just how
important it is to have a proper adjustment.

Thanks for the demonstration.

73
John

==================================

Eric KE6US
6:42pm   #131831

I've only watched it about half a dozen times, but I have a couple of
first/opinionated impressions:

Case 1: Why does anyone care that the dot spring oscillates slightly
when it's clearly pulled away from the fixed contact and in no
position to cause bounce? If the dot weighting is properly adjusted,
there doesn't appear to be any way for the tiny oscillations to cause
bounce. If the dot weighting is not proper, you get bounce on release,
but then the problem isn't one of dot spring oscillations (that's a
secondary effect). The problem is the dot weighting adjustment, and
maybe dot stop adjustment.

Case 2: I don't see that a dit stabilizer does anything other than
allow a little sloppier adjustment of the dot weighting. Again, it
fixes a problem that wouldn't exist if the bug was properly maintained
and adjusted...assuming the original design was good. You can either
fix the problem or attack the symptoms. Only one of those is a real
solution.

Case 3: Good example of an over-damped spring-mass experiment. (hi).
No ringing, but an unresponsive, near lifeless mechanism. To me, the
dot spring is the genius invention in bug design. It extracts work
from the pendulum without seriously affecting it. The pendulum
assembly is merely the engine that drives it. Stiffen the dot spring,
and the engine bogs after a few dits.

I plan to let it rest a little and look at it a few more times.

So far, a very enlightening video, as were the others. This is
valuable stuff, Chris.

Eric KE6US
==================================

Richard Knoppow
6:48pm   #131832

This is very interesting, thank you for setting this up and posting it.
    I notice that in the third test, the one where the stabilizer is
set too close, that the vibrating contact no longer hits the fixed
contact square. I think you would have to twist the fixed contact post
to get it square. I wonder if this makes any difference at all. In the
other two the two hit square although not exactly in line and have a
rubbing effect. The rubbing might cause static if they are dirty but
will also tend to keep them clean.
   It's hard to see the, what shall I call it, parasitic vibration of
the dot spring. I can see it but it looks pretty small. The question
to me is how much movement does the dot contact have in relation to
the fixed contact, i.e. enough to cause static? Probably it depends on
how the bug is adjusted. That is, if the overall motion for dots is
too small the motion of the dot spring will be comparatively a large
part of the total motion of the pendulum where if its larger the small
vibration will not make much difference. I think this is correct, I am
trying to visualize it.
    What I am calling the "parasitic" oscillation is the period of the
small spring and the associated mass. It will depend on the stiffness
of the spring, the length and the mass of the spring and contact.
Beyond me to calculate but it could be calculated. You would have to
know some constants of the spring and dot assembly. You can make the
dot spring vibrate by just tweaking it with your fingers. Could also
get some idea of the damping by how long the vibration takes to decay.
    I have looked at the action of several bugs using a Strobotac but,
since the period of the dot contact is not the same as the main
vibrator the strobe does not stop its action. This slow motion
photography is much more revealing.
    Frankly, I am not sure what to make of this. Since contact noise
can very often be stopped by putting a capacitor across the key one
wonders how useful the dot tamers are.
   Its too hot in Los Angeles.

--
Richard Knoppow
dickburk at ...
WB6KBL

==================================

Richard Knoppow
Sep 29   #131843

The more I look at this and think about it the more I wonder about the
"scratchiness" being from irregular contact surfaces. The contacts
slide over each other. This is true for many self-cleaning contacts,
but it seems to me that if the surfaces are rough the sliding action
may make a static like running a screwdriver over a file. Once the
contacts are polished it wouldn't happen. So, I wonder if the bug
tamers really only work where the contacts are not polished. I don't
know how to go about proving this. I wonder about any other thoughts,
Eric and some others seem to have put some thought into this. These
slo-mo pix are extremely interesting.
    BTW, who else is old enough to remember newsreels in the theater?
Slow motion shots of things like curve balls were popular. I think
they were not more than double speed.

--
Richard Knoppow
dickburk at ...
WB6KBL

==================================

Eric KE6US
Sep 29   #131846

I don't think you can generate static electricity  between two metal
contacts. The triboelectric effect depends on two materials separated
on the triboelectric series, and key contacts would be two identical
metals rubbing against one another. If they were irregular contacts
(scratched, pitted, etc.) you could get intermittent contact that
would look like contact bounce and cause scratchiness, but again,
that's a secondary effect, not a primary effect. The primary effect to
be fixed is screwed up contacts. *No point in fixing anything until
you have a properly maintained, properly adjusted bug as a starting
point. *Foam cubes, dit stabilizers, etc. treat symptoms. They don't
fix problems.

CLEAN contacts are important. And proper CLEANING is important. I
cringe when I hear of someone scraping a piece of bond paper between
the contacts to clean them.  I posted something at length a few months
ago on proper cleaning and others offered their advice. Except for a
few of us who run boat anchor stations, most are using rigs that draw
microamps through the contacts. Aggressive cleaning is detrimental.
They only need a light touch to remove dirt and debris from the air
unless neglected for a long time.

I liked the wiping action of the contacts on Chris's Mac. I think
that's exactly what is needed to keep the contacts clean. I'm also not
bothered by the misalignment of the contacts resulting from the tight
dit stabilizer. That sharp edge could be a problem with keying
circuits that draw some current, but certainly not a problem with my
K2 that draws 650 microamps. I like rounded contacts that slide
against one another. The dot spring on my Begali is a sharp pinpoint
contact that bears against the pendulum to make contact. No U-shaped
flat spring. Seems like that would be the ideal for modern rigs. Not
sure how it would hold up to some boat anchors, and not about to test
it (hi).

Eric KE6US

==================================

Rich NE1EE
Sep 29   #131827

After Chris posted his slomo of his '37 key, I wondered how the DL-150
would work if all I did was adjust the speed. I had earlier adjusted
the weight to 50% because I was going to operate at 10 wpm, and think
that the more uniform spacing will be more acceptable to newer ops. I
removed the extension bar, which mean that this is as fast as this
baby can go, unless I have another lesson to be learned ;-)

https://drive.google.com/file/d/1xzoiPmfWt6pNs7Ibs_1lf81VQdCo_fOo/view?usp=sharing

KN4YB DL-150 bug 20200929a 52wpm
52 wpm !!! 2.3 ms per dit. all the speed that I will EVER need ROTFL
;-) Looks very clean out to the required 8 dits, then seems fairly
good out to 28, before abruptly going solid. As I discovered the other
day, changing the weight will cost dits, but because all we really
need is 9, we are good to go.

...spoke too soon, I see...I glanced over at the key, and saw that the
bar stop was not against the reed, so I engaged it, and reran the
test.
https://drive.google.com/file/d/1nmhXxLHHdiEr42rWs8Dvb60EhCKuiNJf/view?usp=sharing

KN4YB DL-150 bug 20200929b 75wpm
shows uniform dits of 1.6ms, which I'm pretty sure is beyond the range
of bat hearing ;-)



--
72/73 de Rich NE1EE
On the banks of the Piscataqua
==================================

Rich NE1EE
Sep 28   #131795

On 2020-09-27 21:03:-0400, Drew AF2Z wrote:

Just looking at the waveforms I would choose the second one:
KN4YB DL-150 bug 20200927a preadjustment 2

This is the most heavily "weighted" among the set. Weighting here
refers to the duty cycle (not dit/dah ratio). In this case the dit "on
time" is slightly greater than the space between dits. This gives a
good solid string in QRM and noise. It is the antithesis of the
commonly encountered bug misadjustment producing light, feathery dits
that can be very annoying to listen to in an extreme case. (The
lightest weighted waveforms in the set are the last two.)

FWIW, the weighting can be even heavier than that in the 20200927a
waveform above with good effect, producing a very solid string of
dits. However, such adjustment will produce strings that run out of
steam a lot quicker. But as someone mentioned, we never need to send
more than eight dits at a time. I don't see any benefit in adjusting a
bug to produce very long strings of dits. Weighting is the more
important characteristic.

73,
Drew
AF2Z

It's a good comment about weighting. Earlier on this forum (I think)
there was a discussion of weighting, and I "discovered" that at least
2 systems regarded weighting as the amount of time a dit used out of
the dit-dit_space window. That is, if nominally the time for a dit and
the following space is 200 ms, then increasing weight means shifting
time from the space to|from the dit. So an increased dit weight would
be, say, a dit time of 120 ms and a dit_space of 80 ms. Images
available on request.

With regard to the earlier discussion of energy loss in the bug dit
system, on my bug it seems clear that I have 3 significant energy
losses: the scraping of the dit spring contact across the dit screw
(minimized, but not eliminated, by changing dit spring location
(possible on other bugs?) and contact orientation); the dit spring;
and the main pendulum arm spring. The springs are not ideal, so they
are lossy devices, converting flexing into small amounts of heat.

Predictably, then, if we move the dit screw closer to the dit spring,
we might expect two things: greater energy losses, resulting in a
shorter series of dits, and, with a greater dwell time for the dit
spring contact on the dit screw, a change in dit weight. Note that
this only applies to dits on the bug; on a keyer it weight could
affect both dits and dahs.

https://drive.google.com/file/d/1DhwM-nTx7vp4v2vaQ3lPscLeC4JHbpK2/view?usp=sharing
https://drive.google.com/file/d/18wOoWBq47LmFPaazShOvBImBGPgNCqqn/view?usp=sharing

KN4YB DL-150 bug 20200928a insert dit screw ~1 turn 1
illustrates that the dit string now runs out of energy ~5.5s, which is
plenty of time. Note also that the weight changes gradually during
those 5s, but there is little change in the first 2 s.

KN4YB DL-150 bug 20200928a insert dit screw ~1 turn 2 120ms 100ms
indicates the new weighting. dit time of ~120 ms is still 10 wpm, but
the dit_space is down to 100 ms.

https://drive.google.com/file/d/1PchjDQaXuTGY4YDinJ4umcX9Z1bBLv6-/view?usp=sharing
https://drive.google.com/file/d/1Esh-RNHkGKQ161_VKCWKuc1MkOuRdmvl/view?usp=sharing
KN4YB DL-150 bug 20200928b insert dit screw max dit weight 1
KN4YB DL-150 bug 20200928b insert dit screw max dit weight 2 135ms 85ms

These show that the dit stream is reduced at the expense of weight.
Happily, the dit time is increased by the same amount that the
dit_space is reduced, keeping the over all wpm fairly constant. At 10
wpm, the change in weight might not be useful. And I guess that while
I have the tools here to detect the changes, I don't hear a noticeable
difference at 10 wpm. The guideline here /might/ be to adjust
everything to your liking, and then adjust the dit screw for a minimum
dit stream (9 in this case), which yields the greatest weight.

The cheeky comment about new ops not knowing the importance of weight
didn't pass unnoticed. Not helpful. When I was first learning to
drive, I was traveling on a country road with narrow shoulders, and
arrived at a point where I was going to pass a car parked on the
opposite shoulder, and there was an oncoming car. The oncoming driver,
rather than slow down and wait until it was safe to pass, expected me
(reasonably enough) to pull to the right, rather than wait until it
was "safe" to pass. I didn't. Scary moment. Lesson learned about
"situational awareness" was one I have /never/ forgotten. I am now a
much better defensive driver, analyzing driving patterns around me as
a force of habit, and anticipating changes.

I was once new to driving a car, an 18-wheeler, an airplane (you know
the ones...those little 2 seaters the Navy launches from carriers),
SCUBA diving, and driving a motorcycle. Every one of those requires
some serious learning to do it well. In some cases, just to survive.

I took the time to do all this in part as a self-learning exercise,
knowing that what I write down and analyze helps me learn, but in part
because I hope that others can learn from the results. I've been
thinking of writing stuff up and posting on my web site, not as an
expert, but as FYI. For me, it's the journey. I once thought of bugs
as keys from hell, to be used by a select group of ops who like life
as complicated as possible. Now I find myself embracing the one I
have, but only after I have studied it and experimented. OTOH, I just
plugged in my straight key, and went to work.

This DL-150 key by KN4YB is not a Bengali, but I think that it works
swell, and does exactly what I need a bug to do for me. I also like
the right angle setup. The base is very heavy, and the right angle
makes it less likely (I guess, not having used the inline version) to
move around. It comes in a version where the wires are all beneath,
and one like mine, which uses top posts. I ordered it with top posts
because I think that it looks more traditional.



-- 
72/73 de Rich NE1EE
On the banks of the Piscataqua

==================================



73

DR