[dorkbotsea-blabber] Looking for someone mechanically inclined

[Steve Greenfield]

Not sure how to describe this in words...

Put a sprocket in the center. Run an arm out from the center (not connected to the sprocket). Put another sprocket of the same size on an axle at the end of the arm. Run a chain around both sprockets.

Now if you hold the center sprocket steady and rotate the arm around, the sprocket on the end of the arm will stay lined up with the center sprocket. Turn the center sprocket and the outer sprocket rotates exactly as the center sprocket does, regardless of where or what the arm is doing.

Make the arm the Hour hand. Connect the center sprocket to the drive for the Minute hand, and attach a Minute arm to the outer sprocket. Now the Minute hand will be at 90/180/270/360 for 15/30/40/60 minutes regardless of where the Hour hand is.

Just extend that with the Second hand with a couple of linked transfer sprockets at the end of the Hour arm.

 Steve Greenfield 



----- Original Message ----
From: Brett Wagner <brett at madhouse.org>
To: A discussion list for dorkbot-sea <dorkbotsea-blabber at dorkbot.org>
Sent: Monday, September 1, 2008 5:46:17 PM
Subject: Re: [dorkbotsea-blabber] Looking for someone mechanically inclined

Just to frame the discussion a bit, I want to build a real version of a 
little piece of code i wrote a couple of moths ago.  Basically it's a 
nested epicycloid clock: http://islandzero.com/?q=node/3

For those not Flash enabled, imagine a clock where the origin of the 
minute hand rests on the end of the hour hand and the origin of the 
second hand rests on the end of the minute hand (At noon it would look 
like a long vertical line but at 6:15:00 it would look something like 
|_|) .  I'd like to mount the whole apparatus behind a bit of frosted 
glass and have the far end of the second hand etch the glass using, I 
assume, a chip of industrial diamond.  The other thought would be to 
size the whole thing up take it out to burningman and have it etch the 
playa.

Now if I wanted to take the easy way out I could simply put a stepper 
motor at each origin and drive the whole thing that way. However I'd 
rather take the route that is going to be both more aesthetically 
pleasing and mentally challenging and try to run the whole thing from 
one center-mounted stepper using gearing and roller chain to 
'communicate' the motion out to the outer origins.

There are a few problems that I solved in software that are puzzlers for 
me mechanically that aren't solved by traditional clock movements.  You 
will notice in the refined flash version that I linked that the minute 
and second had point the "proper" way, independent of their parents (IE 
at 5:30 the minute hand points down rather than backwards down the hour 
hand as it would if it were not artificially corrected). I'm thinking 
this might be a problem I solve in 2.0.  I also have various concerns 
about hand sag and general lack of machining knowledge thats going to 
bite me on the ass I'm sure.

I'm finding https://sdp-si.com/ to be pretty damned incredible in terms 
of what can be sourced.  I having to work past some vocabulary issues 
though. Since I have only the most cursory exposure to any kind of 
mechanical engineering ( I never set foot in shop class in high school, 
but I can set up and do basic repairs on a Hilderberg printing press to 
this day ;) ), I have to hit wikipedia pretty hard to determine what is 
meant by pitch diameter, hub diameter, face width, etc.

... so yeah, comments, suggestions, odds that I'll ever get the damn 
thing done to my liking?