Subject:
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Re: Design Question - For a newbie
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Newsgroups:
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lugnet.robotics
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Date:
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Wed, 29 Dec 1999 10:51:47 GMT
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Viewed:
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1596 times
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Phil Watt wrote:
> The R2D2 of the DDK uses this drive forward - turn in reverse with the one motor
> that the micro-scout has. It could also be done with a differential and a
> ratchet on one wheel. The ratchet would allow both wheels to move forward, but
> would only let one turn in reverse. Then setting a timing loop for an
> "about-face" should work
http://www.cgl.uwaterloo.ca/~anicolao/lego/droid_wheel.html shows how to
build this assembly, which was what I was going to suggest. It only
works if your droid is a three-wheeler, with this wheel as the nose
wheel, but is very effective at maximizing the DDK's single motor. It's
possible to do the same idea with a normal drive train driving the rear
wheels and either a single front wheel or two front wheels that are
"caster wheels" like those on the front of a shopping cart. By blocking
the travel of the caster you can make the reverse direction into a turn
while forward motion will right the caster and travel straight. (Erik
Brok's lego on my mind site includes a caster wheel design, I think ...
it is linked from ttp://www.crynwr.com/lego-robotics/ - I would have
provided a direct URL but the site seems to be down right now).
While I'm on the topic of the DDK, I have a question for other DDK
owners: is your constructopedia falling apart? Mine fell apart on first
use, which made scanning the pages easier but is otherwise very
frustrating...I guess I need to contact Lego Canada :-(.
> > But then I can't figure out
> > how to "fire" the gun. I planned on setting a motor running when a touch
> > event occurred which would "push" the trigger of the firing mechanism
> > launching the projectile.
With a two rubber bands and a "bent" technic piece it should be possible
to build a mechanical trigger that stays one way until hit and swings
all the way the other way (to fire the bullet) after being touched. You
sometimes see these types of spring-loaded mechanisms on screen doors,
to help keep the door shut when it is shut but move easily out of the
way when it is opened ... a mechanical solution saves the second motor
for some different use (unless you want to fire more than once, a
complicated problem in itself since you must load a new bullet).
> > OK, on to the question, has anyone built a simple robot to do something like
> > this? How did you overcome the obstacle of only having 2 motors? I
> > understand that the RIS and RCX have 3 outputs and can control 3
> > simultaneous motors, but unfortunately I don't have that luxury.
As an aside, even RIS purchasers only get two motors - you have to buy a
third separately or as part of another set (a second RIS, or the
RoboSports expansion kit - the expansion sets seem to have a bad
reputation on this mailing list which I at least feel is undeserved).
alex
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Message is in Reply To:
 | | Re: Design Question - For a newbie
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| One way to have the Scout drive and shoot would be to use one motor to drive forward and turn in reverse, then use the second motor to fire the "bullet". The R2D2 of the DDK uses this drive forward - turn in reverse with the one motor that the (...) (25 years ago, 30-Dec-99, to lugnet.robotics)
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