Subject:
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Re: November 2004 SMART Meeting Notes
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Newsgroups:
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lugnet.org.us.smart
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Date:
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Mon, 22 Nov 2004 18:42:34 GMT
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Viewed:
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2868 times
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Thanks David for organizing this meeting. It looks like I missed a lot of cool
robots. Good job Mark on a excellent mini-challenge robot. From the photos I
can see that there were several other cool robots that I wish I had more time to
look at.
David, really nice job on the NQC PowerPoint presentation. I'm sure that was
very well received. The examples were clear and an excellent choice to show why
this technique is so useful.
A few more tidbits on the clock: It has a total of 29 gears including the 24t
differential gear that I use to hold the hour hand. The gear ratio from the
weight spool to the escapement gear is 27:1. Since the 2m string wraps around
the spool almost 40 turns and the 8 tooth escapement gear makes one rotation
every 8 seconds, the clock can run for about 8*27*40 = 8,640 seconds (2.4 hours)
before the string is all the way out. From the escapement to the second hand
there is a gear ratio of 15:2. Therefor for the second hand to make one complete
rotation, the escapement gear needs to turn 15/2 = 7.5 rotations. Since the
escapment gear takes 8 seconds to make one rotation, it takes 8 * 7.5 = 60
seconds for the second hand to make one rotation. From the second hand to the
minute hand the ratio is 60:1 and then from minute hand to hour hand it is 12:1.
According to my calculations, the weight drops about .23 mm every second. This
drop in the weight is the sole source of power to keep the pendulum swinging and
drive the hands of the clock, not to mention all the supporting gears.
Here is a link to a site that shows clock and watch escapement mechanisms in
motion. This was very helpful for me to understand the fundamentals of how an
escapment needs to work but in the end I could not see how any the escapement
mechanism that it shows could be built out of Lego.
http://www.geocities.com/CapeCanaveral/Hall/3934/escapement.html
The escapement mechanism I choose was not one of these but rather was inspired
by a clock that I saw at the London science museum.
http://www.sciencemuseum.org.uk/on-line/huygens/page3.asp
The advantage of this escapment mechanism is mainly that it does not require
precisely angled pallets to work.
Gus
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Message is in Reply To:
 | | November 2004 SMART Meeting Notes
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| We had a small but wonderful meeting last weekend! Gus showed a wind-up clock that he's been working on. He gave an interesting presentation on how several escapement mechanisms work, and also some useful pointers on how to reduce friction in gear (...) (20 years ago, 22-Nov-04, to lugnet.org.us.smart)
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