Subject:
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Re: CD auto feeder project
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Newsgroups:
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lugnet.robotics
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Date:
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Sat, 8 May 2004 00:00:48 GMT
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Original-From:
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Steve Baker <sjbaker1@airmailSTOPSPAM.net>
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Viewed:
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954 times
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David Glynn wrote:
> This might of course be pie in the sky and beyond the limits of the RCX
...maybe - but you could do it with TWO RCX's! Remember, they can talk to
each other via IR.
The RCX has three motor ports and three sensor ports (although you only
get two motors in the set)...I think that's plenty for this application.
> I figure I need two motors (and a third for the pneumatics)
Perhaps - but often you can figure clever mechanical solutions to
save a motor.
In this case, you might (for example) have one motor to rotate the arm
over the appropriate drive tray or input hopper - and one to lower the
pneumatic sucker onto the CD - and raise it again to lift it off the stack...
so you might assume you need a third for operating the pneumatics...but there
is a trick.
If you build a differential gear (like on your car's drive axle) - then the
motor can drive two axles at once. It'll feed the power to whichever axle
rotates most easily. Perhaps then it can drive the arm downwards - and
when it hits the CD, that axle won't rotate easily anymore - so the second
axle will get the power and can be used to operate the pneumatics. Once you've
got the CD, you could reverse the motor - once again the lifting shaft will
be easy to turn - the pneumatics won't be operated until the lifting shaft gets
stuck again...at which point you can arrange it to drop the CD.
It'll take a bit of jiggling with gears and rubber bands and stuff to get it
to work - but it's almost certainly possible.
Alternatively, you could put a vertical rod beside the pile of CD's such that
some part of the pneumatics gets pushed on as the main arm lowers - which causes
it to operate.
Part of the 'fun' of building complicated machines with a single RCX set is
in divising sneaky little tricks like this. When you have dozens of motors
and a bunch of RCX's, you tend to get lazy.
Take a look at a machine like the infamous 'Furby'. It has just ONE cheapie
motor and it can independently blink, move it's mouth, swivel it's eyes, wiggle
it's ears and 'dance' by tipping back and forward! Find an old one and
look inside - it's really ingenious. Quite an inspiration.
> two touch sensors - one on the bumper style sucker head so as not to mash the CD down
> too far (do I need another so that I don't raise it too far?)...
Maybe you don't need this. There is a 'clutch gear' in the RCX set that will
transmit power until a certain force is applied to it - then it'll slip. You
can do the same thing with a belt-drive - again, it'll drive until the output
shaft gets 'stuck' then the drive band will slip.
A pair of bump sensors is a little more elegant - but you can't always afford
elegance.
You can also connect two bump sensors in parallel onto one RCX port. You can't
tell which sensor is pressed - but if you are moving the arm down - and a sensor
triggers, it's gotta be the bottom one - and if you are moving up - it's gotta
be the top one. That frees up another sensor port.
> and the second
> at some point in the rotation to calibrate the arm and finally a rotation
> sensor so that it can count from one stack to the next.
You can use a light sensor to do the same thing (since you don't get a rotation
sensor in the RCX set) - put a pattern of black and white bricks at each 'station'
where the arm can reach and write yourself a barcode reader so you know where you
are. Since the rotation sensor has a tendancy to gain and lose counts, this is
a better solution because it doesn't accumulate errors over time.
> There is also the
> need to close the CD drive once the disc has been loaded, this can either be
> done through pressing the switch on the front, or be hacking into this micro
> switch and just having to close this circuit briefly.
On just about every CD drive I've seen, you can just push the drive tray to make
it close. You could make a lever that gets pushed when you move the CD-lifting
arm out of the way that mechanically pushes on the drive tray.
Another thing I've found valuable when solving these kinds of problem is to
realise that you can sometimes change the problem.
For example - you could keep a carosel of blank CD's ABOVE the CD drive tray
and build a mechanism to drop the bottom-most CD into the tray...or maybe
you could use the fact that the PC opens it's drive tray to push on a lever
that causes the finished CD to be flipped out so you don't have to pick it
up. A big funnel underneath could catch the ejected CD's and stack them
without any moving parts at all!
I'm not saying that any of these ideas are any good - just that you should
look for wilder solutions than just trying to exactly replicate a machine
that you've seen before.
Remember - one guy built an entire functioning computerised keyboard and
printer with ONE RCX!
---------------------------- Steve Baker -------------------------
HomeEmail: <sjbaker1@airmail.net> WorkEmail: <sjbaker@link.com>
HomePage : http://www.sjbaker.org
Projects : http://plib.sf.net http://tuxaqfh.sf.net
http://tuxkart.sf.net http://prettypoly.sf.net
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Message has 1 Reply:
 | | Re: CD auto feeder project
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| (...) Or multiplex bump sensors mechanically...use one touch sensor on a cam on an axle, normally pressed in and held centered with a rubber band. Any number of "inputs" can be hooked up perpendicular to the axle using an bumper connected to a push (...) (20 years ago, 12-May-04, to lugnet.robotics)
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Message is in Reply To:
| | Re: CD auto feeder project
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| Rob, Thanks for posting the new link to your website. I spent a bit of time going over the Window Walker making sense of the pneumatics and was about to reply and thanks you, when I went to browse the rest of you site. You site is a gold mine! (...) (20 years ago, 7-May-04, to lugnet.robotics)
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