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I broke another 9V motor. See my original post for the first story.
I’m building what amounts to a pitching machine for the Great Ball Contraption.
In most TECHNIC building you’re building a gear train to produce lots of power
at the expense of speed. But in this case I need to build one that has lots of
speed and not much power.
I have a tire that spins very quickly, and as the soccer balls roll past it
they are accelerated and launched into the air. It’s really cool, and I’ve been
working with a prototype structure to hold it all together, so it’s flimsy.
Eventually I want to rebuild it to withstand day-long use, and that also means
fixing the gear train, because I’ve broken two motors with it so far.
In the prototype, I put a clutch gear right on the motor output, but even with
that precaution the motor has a hard time turning if something completely stops
the spinning tire. In both motors, something inside them eventually broke under
the strain, so now they are very difficult to turn. I definitely want to avoid
this in the future.
I have no camera available at the moment to show you what it looks like, so I’ll
do my best to describe the gear setup.
The motor has a clutch gear on its shaft. This is attached to a 40 tooth gear
with a chain. On the other end of this gear’s axle is another 40 tooth gear with
another chain going to a 16 tooth gear on a third axle. This spins another 40.
This 40 turns an 8 tooth gear on a fourth axle, which also turns a 24 tooth
crown gear, which turns an 8 tooth gear on a fifth axle. This last axle has the
tire on it.
If you can sort that out in your mind, this means the tire is spinning
quickly. Very, very quickly. It is fast enough that trying to stop it with
your finger is very easy, and that’s when the motor stalls. Actually, it doesn’t
technically stall; it still turns inside the clutch gear, but it has to work
very hard to do so.
What advice can you give me to avoid breaking any more motors? The clutch gear
works in normal gear trains because the motor doesn’t have to work very hard to
begin with: it spins quickly and produces lots of torque farther down the line.
But here I’m doing the opposite. If I had an RC motor I would try using that,
since they are more powerful, but right now I’m stuck with normal 9V motors. Oh,
I also have one of those weird motors (no axle, but an axle hole) from the
monkey set, but I don’t know how it compares to regular ones.
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I thought of something else. I’m testing this thing with an RCX, and could it be
that as the batteries get weaker the motor loses power, which makes stalls even
more dangerous?
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In lugnet.technic, Jordan Bradford wrote:
> If you can sort that out in your mind, this means the tire is spinning
> {quickly}. Very, {very} quickly. It is fast enough that trying to stop it
> with your finger is very easy, and that's when the motor stalls. Actually, it
> doesn't technically stall; it still turns inside the clutch gear, but it has
> to work very hard to do so.
>
> What advice can you give me to avoid breaking any more motors? The clutch
> gear works in normal gear trains because the motor doesn't have to work very
> hard to begin with: it spins quickly and produces lots of torque farther down
> the line. But here I'm doing the opposite. If I had an RC motor I would try
> using that, since they are more powerful, but right now I'm stuck with normal
> 9V motors. Oh, I also have one of those weird motors (no axle, but an axle
> hole) from the monkey set, but I don't know how it compares to regular ones.
This may not eliminate stalls, but try adding a bunch of
spinning mass (i.e., a flywheel) somewhere in your gear
train, preferably at the output. A big Technic tire
(like from 8448 or something similar) would work nicely
for this. This will at least make it more difficult
to stop the gear train once the flywheel is spinning.
Could you try softer (balloon-type) tires on your ball
launcher, to make it more tolerant of imperfect
spacings?
To do both, try something like Philo's Hammerhead CD
launcher:
http://www.philohome.com/hammerhead/hammerhead.htm
You're right about clutch gears, they generally work
best when gearing down rotation speeds. Perhaps you
could gear down some, then gear back up again?
I've found that RC motors, while very powerful, stall
in a nasty way: you have to cut the power to get them
unstuck again (the thermistor needs to cool down).
Just a few random ideas...
-Tim
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Update: there are now two motors driving this thing. They each have an 8 tooth
gear that turn a 40-tooth gear placed between them -- instant torque, but less
output speed. I put another 40-tooth gear on the same axle as that one and
connect that with a chain to the clutch gear. Now if the tire gets stuck, the
clutch gear has enough input torque to keep turning, meaning my two motors
aren’t stalling. The tire isn’t spinning as fast as it used to, but it’s still
good enough to shoot out balls.
I also wondered if my RCX batteries’ getting weaker might have affected things,
since lower voltage == lower motor speed, so I’m now powering the two motors
from a train speed regulator turned on all the way. Now the input voltage is
constant.
The suggestion to use a rotation sensor is good, except that I need my RCX for
the mine shaft rescue competition at Brickfest. So, the ball launcher has to
remain mechanical only. The flywheel idea didn’t work because I barely have to
touch the tire to stop it, and a lot of spinning mass wouldn’t change this. For
the same reason, a slipping system using pulleys wouldn’t work: there’s not
enough torque for it to slip.
Now I get to rebuild my contraption, because its structure is too fragile --
it’s a prototype.
Oh, doesn’t the RCX have a current-limiting device in its outputs? I don’t think
the train regulator does. If that is the case, I could use my other RCX, which
is happily version 1.0 and has an AC adapter jack. I was going to use this for
another part of my GBC contribution, but it was just as a glorified power
supply.
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> I'm building what amounts to a pitching machine for the Great Ball
> Contraption. In most TECHNIC building you're building a gear train to produce
> lots of power at the expense of speed. But in this case I need to build one
> that has lots of speed and not much power.
You might also use a fast 2838 motor http://www.peeron.com/inv/parts/2838c01 to
direct-drive the ball throwing wheel. A friend used this setup in a GBC module
http://gallery.freelug.org/Summer_AFOL_Days_2005/Philo_Reims_2005_27 that worked
several hours without motor problems.
Philo
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On Mon, July 18, 2005 4:48 am, Philippe Hurbain said:
> > I'm building what amounts to a pitching machine for the Great Ball
> > Contraption. In most TECHNIC building you're building a gear train to produce
> > lots of power at the expense of speed. But in this case I need to build one
> > that has lots of speed and not much power.
>
> You might also use a fast 2838 motor http://www.peeron.com/inv/parts/2838c01 to
> direct-drive the ball throwing wheel. A friend used this setup in a GBC module
> http://gallery.freelug.org/Summer_AFOL_Days_2005/Philo_Reims_2005_27 that worked
> several hours without motor problems.
>
> Philo
Hey Philo!
I was looking at the 'Summer Days' pictures. It looks like you guys had a bunch of
fun, but many questions came to mind.
I couldn't find a good picture of the Spybot-Train-GBC (GBB) module
(http://gallery.freelug.org/Summer_AFOL_Days_2005/Philo_Reims_2005_55) until I
looked into another directory (see below)
So, how much water could these bridges hold, and why don't you have pictures of them
failing: http://gallery.freelug.org/Summer_AFOL_Days_2005/Philo_Reims_2005_61
Which car went the farthest (what exactly was the
contest?)ttp://gallery.freelug.org/Summer_AFOL_Days_2005/Darkbaron_86
(I'd pick this car: http://gallery.freelug.org/Summer_AFOL_Days_2005/Darkbaron_12)
So, I went looking for pictures of the Spybot-Train, and I found the Weekend GBB
directory...
http://gallery.freelug.org/we_GBB_050605
Now, this is the stuff you need to post. We all get to see your finely tuned GBC
modules, which usually appear to be a work of art. It's nice to see a few
not-so-perfect modules, like those that can't keep up, or the one lifting a bunch of
balls, that has a hand below, to catch pieces that fall off...
Nice video & pictures of something that I know was a fun time... :)
Steve
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Hello Steve!
>
> I was looking at the 'Summer Days' pictures. It looks like you guys had a bunch of
> fun, but many questions came to mind.
Yes, it was a great time!
>
> I couldn't find a good picture of the Spybot-Train-GBC (GBB) module
> (http://gallery.freelug.org/Summer_AFOL_Days_2005/Philo_Reims_2005_55) until I
> looked into another directory (see below)
Actually the best picture is here
http://www.freelug.org/article.php3?id_article=407 (but all text info is in
French...). More on that module on my website in some future! (I also need to
add an update on my ball pump module that I tuned after it failed a few times
during weekend GBB - the new version works flawlessly now)
>
> So, how much water could these bridges hold, and why don't you have pictures of them
> failing: http://gallery.freelug.org/Summer_AFOL_Days_2005/Philo_Reims_2005_61
About 20 kg. Actually no one really failed, except this one
http://www.maj.com/cgi-bin/gallery.cgi?i=203302 (but it didn't fall on the floor
since the bucket was just an inch above ground). Actually the only dramatic
failure was the belt used to support the bucket which broke during the last
attempt ;o)
>
> Which car went the farthest (what exactly was the
> contest?)ttp://gallery.freelug.org/Summer_AFOL_Days_2005/Darkbaron_86
> (I'd pick this car: http://gallery.freelug.org/Summer_AFOL_Days_2005/Darkbaron_12)
Unfortunately there was an organisation problem for that event and no winner:
several cars reached the maximum distance, and quite a few couldn't even be
launched :(
>
> So, I went looking for pictures of the Spybot-Train, and I found the Weekend GBB
> directory...
> http://gallery.freelug.org/we_GBB_050605
>
> Now, this is the stuff you need to post. We all get to see your finely tuned GBC
> modules, which usually appear to be a work of art. It's nice to see a few
> not-so-perfect modules, like those that can't keep up, or the one lifting a bunch of
> balls, that has a hand below, to catch pieces that fall off...
Lack of time... Even the GBB event report in French was very long to come by...
Philo
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On Mon, July 18, 2005 10:51 am, Philippe Hurbain said:
> Actually the best picture is here
> http://www.freelug.org/article.php3?id_article=407 (but all text info is in
> French...). • ...
> More on that module on my website in some future! (I also need to
> add an update on my ball pump module that I tuned after it failed a few times
> during weekend GBB - the new version works flawlessly now)
What was the problem?
> Lack of time... Even the GBB event report in French was very long to come by...
I totally understand that. You'll notice the complete lack of write-ups of most of
my modules. I did come across the above page a little earlier today. I ran it
through babblefish, and here is my favorite line about the "Grand Bidule à Balles"
(which translates to "Large Thingummy with Balls")
"...[it was fun] even if sometimes one [has to] run after the few balls which refuse
to undergo torture..."
Steve
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(I also need to
add an update on my ball pump module that I tuned after it failed a few times
during weekend GBB - the new version works flawlessly now)
|
What was the problem?
|
Minor one: the contraption I used to maintain the liftarms forming the ball tube
spaced 2.5 (based on  ) got loose with time,
now replaced with
 +
Major one: the stirring blade was sometimes blocked by a ball half-engaged in
output drain. Either the motor got stalled, or -funnier- the plastic elasticity
built-up energy and BZOIIING! threw balls across the room...
I replaced the liftarm 1x4 with  , enough
to make balls move, but that can easily slide below blocked balls.
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through babblefish, and here is my favorite line about the “Grand Bidule à
Balles” (which translates to “Large Thingummy with Balls”)
“...it was fun even if sometimes one has to run after the few balls which
refuse to undergo torture...”
|
:-D
Philo
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In lugnet.technic, Philippe Hurbain wrote:
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I’m building what amounts to a pitching machine for the Great Ball
Contraption. In most TECHNIC building you’re building a gear train to produce
lots of power at the expense of speed. But in this case I need to build one
that has lots of speed and not much power.
|
You might also use a fast 2838 motor http://www.peeron.com/inv/parts/2838c01
to direct-drive the ball throwing wheel. A friend used this setup in a GBC
module http://gallery.freelug.org/SummerAFOLDays2005/PhiloReims200527
that worked several hours without motor problems.
Philo
|
Hmmmm. I have but one of the ungeared 9V motors, and I’m using it in a ball
pump, but I will try swapping motors.
If I geared it up just a bit to handle the 90 degree angle (8-tooth gear to
24-tooth crown gear), do you think that would be dangerous?
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In lugnet.technic, Jordan Bradford wrote:
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In lugnet.technic, Philippe Hurbain wrote:
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| |
I’m building what amounts to a pitching machine for the Great Ball
Contraption. In most TECHNIC building you’re building a gear train to
produce lots of power at the expense of speed. But in this case I need to
build one that has lots of speed and not much power.
|
You might also use a fast 2838 motor http://www.peeron.com/inv/parts/2838c01
to direct-drive the ball throwing wheel. A friend used this setup in a GBC
module http://gallery.freelug.org/SummerAFOLDays2005/PhiloReims200527
that worked several hours without motor problems.
Philo
|
Hmmmm. I have but one of the ungeared 9V motors, and I’m using it in a ball
pump, but I will try swapping motors.
If I geared it up just a bit to handle the 90 degree angle (8-tooth gear to
24-tooth crown gear), do you think that would be dangerous?
|
WOAH.
I don’t think I’ll gear it up at all. This thing’s speed is now insane! The
sound it makes is actually frightening.
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In lugnet.technic, Jordan Bradford wrote:
>
> If I geared it up just a bit to handle the 90 degree angle (8-tooth gear to
> 24-tooth crown gear), do you think that would be dangerous?
I don't think it could be dangerous for you (except perhaps a ball thrown in the
eye?), but it may hurt your LEGO parts... when I dismantled my CD-launcher, one
of the 2x1 Technic brick bearing the fast axle had a much bigger hole than
originally, the plastic missing was melted on the axle! (strangely enough, the
launcher was still working well...)
>
> [WOAH].
>
> I don't think I'll gear it up at all.
That's wise. The motor would be too weak to provide some torque after speed
multiplication.
> This thing's speed is now {insane}! The
> sound it makes is actually frightening.
Yep, my friend's GBC module makes a nice machine gun noise when supplied with
many balls ;o)
Philo
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