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In lugnet.technic, David Laswell wrote:
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In lugnet.announce.moc, Shaun Sullivan wrote:
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As is my tendency, here’s an absurdly long treatise describing the
development of a LEGO Train Odometer Car (a.k.a. the “LEGOdometer”).
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Interesting. I thought this might be interesting to use in our
displays...until I read that it binds up in reverse. When we lose a car for
whatever reason (often some young kid’s hand straying where it ought not to),
we usually recouple by running the train in reverse to pick up the
stragglers. Perhaps your next iteration could have a slip gear system that
disengages in reverse and engages when going forward?
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That’s something I hadn’t considered. Fortunately, unless it’s run backwards
for a long time, it probably won’t be an issue. It takes a good while to take
up the lash in all of the gears in the opposite direction; the overall gear
reduction is 1:1685.099 over 9 different gear pairs. That translates to plenty
of distance before the hundreths wheel starts runing in reverse.
On top of that, the first ratchet is actually on the second dial, the tenths
place. As a result the gear train won’t actually bind up until the engagement
on the tenths dial has run backwards and tries to turn the spoked pin joiner
backwards.
Short story: it’s unlikely that the car will bind up unless it’s running
backwards for a while.
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As Dave Eaton likes to point out, the length of the outside rail on a
circular train track will be longer than the length of the inside rail.
This same effect holds true with nearly all train layouts that are seen in
shows; the length of one of the rails will be longer than the other. So the
question becomes – what do we truly want to measure? The distance the train
has gone around the outside rail? The distance along the inner rail? Or
some distance in between?
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I would think it would measure the outer rail at high speeds and the inner
rail at slow speeds. The reasoning is that at slow speeds, assuming the
motor bogey is pulling rather than pushing, it will pull the train against
the inside rail so there will be more friction on that side of the bogeys.
At high speeds, however, momentum comes into effect, and if you’ve ever
watched a LEGO train moving at significant speed, anything but the most
lightweight of cars will heel over a bit when it slams into the curve, so the
inner wheels will actually lose contact with the rails for a bit as they lift
up, while the outer wheels will be pressed into the rail.
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That’s another good point. Based on your observation at high speeds even a
differential won’t be truly accurate; in fact, it could be much worse! If the
inner wheels lose contact altogether, then an averaging differential will give a
value between “fast” and “stop” - which would correspond to a much smaller
distance than even the inner rail alone would produce.
Hmmm, that might be a good argument to stick with the solid axle!
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Shaun Sullivan wrote:
> That's another good point. Based on your observation at high speeds
> even a differential won't be truly accurate; in fact, it could be
> much worse! If the inner wheels lose contact altogether, then an
> averaging differential will give a value between "fast" and "stop" -
> which would correspond to a much smaller distance than even the inner
> rail alone would produce.
A differential might have other problems. I seem to recall that use of
differentials was explored in geared locomotives (such as Shay, Climax, and
Heisler), and was abandoned because the differential caused power loss in
curves. (reference here: http://climaxlocomotives.com/history/ ). Not sure
if that would translate in reverse to an issue.
Frank
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In lugnet.technic, Frank Filz wrote:
> A differential might have other problems. I seem to recall that use of
> differentials was explored in geared locomotives (such as Shay, Climax, and
> Heisler), and was abandoned because the differential caused power loss in
> curves. (reference here: http://climaxlocomotives.com/history/ ). Not sure
> if that would translate in reverse to an issue.
Well, if a real train hits curves in any manner similar to how a LEGO train
does, then the inside wheel will probably lift up enough to at least slip on the
rail, which would result in that very effect. On the plus side, as it loses
power, it will lose speed, and the inner wheel will sit more firmly on the rail,
thus allowing it to pick up speed again. :D
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In lugnet.technic, Shaun Sullivan wrote:
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That’s something I hadn’t considered. Fortunately, unless it’s run backwards
for a long time, it probably won’t be an issue. It takes a good while to
take up the lash in all of the gears in the opposite direction; the overall
gear reduction is 1:1685.099 over 9 different gear pairs. That translates to
plenty of distance before the hundreths wheel starts runing in reverse.
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True, but then you’re losing the count on some of the distance traveled. I
thought of a better option to all of this, though. I can’t remember who it was,
but someone (don’t even ask me to remember who, or where to find this) came up
with a gear system that turned +/- input into + output. That is, regardless of
which way you turned the input source, the output constantly turned in one
direction. Incorporating this into your design would allow the odometer to
continue adding in both directions, though you would have to remember to make
sure you faced the correct side outwards.
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On top of that, the first ratchet is actually on the second dial, the tenths
place. As a result the gear train won’t actually bind up until the
engagement on the tenths dial has run backwards and tries to turn the spoked
pin joiner backwards.
Short story: it’s unlikely that the car will bind up unless it’s running
backwards for a while.
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Is this something that would make a difference based on how recently it has
flipped the tenths dial? For example, if it has just flipped the dial far
enough to trip the turnback catch mechanism, will running it backwards result in
a significantly shorter distance to where it binds than if it was just on the
verge of pushing the dial past the catch?
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