Subject:
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Re: SSClagorpion
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Newsgroups:
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lugnet.technic
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Date:
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Fri, 16 Apr 2004 16:52:19 GMT
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Viewed:
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8880 times
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In lugnet.technic, Kevin L. Clague wrote:
> In lugnet.technic, Steve Hassenplug wrote:
> > In lugnet.technic, Mark Bellis wrote:
> > > A few things spring to mind about this:
> > >
> > > 3. The model is going to walk, so the force on each leg is potentially a dynamic
> > > one, if it walks fast enough. When you jump repeatedly, the force on your legs
> > > is not equal to your weight, but significantly more - at least double,
> >
> >
> > That makes sense, but you may want to take a look at the video of Kevin's
> > walkers:
> >
> > http://www.kclague.net/Quad242/q242-forward.mpg
> >
> > As you see, at the end of each stride, all four legs are at the bottom of their
> > travel. So while it is true that half the legs will have to support all the
> > weight, I don't think the force on the legs will ever be above the weight of the
> > walker.
> >
> > It's pretty cool the way it walks. I'm not exactly sure what it's doing, it
> > must be some kind of black magic...
>
> Funny! My presentation at Brickest (classic?) was named Pneumatic Magic.
>
> When I started on quad242 I thought the cool thing was going to be the ability
> to make it modify its behavior to go backwards and turn, but the hardest part
> was the "no gravity well" concept you point out above Steve.
>
> > > I suggest you make a trial compressor engine using a pair of 8475 RC buggy
> > > motors geared down and four pump cylinders with springs removed, with cranks
> > > offset at each 90 degree angle. Offsetting the pumps by 90 degrees should make
> > > the load on the motors smoother. The engine will need to be very strong due to
> > > the torque required. I suggest two shafts geared together, supported by double
> > > width beams throughout. Use 40 tooth cogs to make the cranks as they're more
> > > sturdy than other crank parts and will allow you to gear the two shafts together
> > > easily.
> >
> >
> >
> > Yes, Kevin was just talking about using beams for strength throughout the model,
> > instead of the lighter liftarms he often uses.
> >
> > I'm hoping he has some experience with compressors. If not, I'll have to throw
> > together something using the buggy motors. Thanks for the idea.
>
> I have some experience with compressors.
>
> I've worked out a perfect geometry for large pumps so that they can be pumped by
> a motor and use the entire piston head travel range. This was one of those holy
> grail kinds of things.
>
> There has been a long standing debate about which are better small pumps vs.
> large pumps. C.S. Soh is set on small pumps, and he actively scorns those who
> use them (well at least me anyway.) I've seen good arguments for large pumps
> also.
>
> If we go with four pistons per leg (more volume with less pressure), I for sure
> think that large pumps are the way to go. It is hard to acheive high pressure
> with LEGO pneumatics, but it is not nearly as hard to get the volume up. I'm
> still pondering the 2 vs. 4 scenario.
>
> I've got a pretty strong 2 piston hip/leg assembly going. The hip pivot is very
> sturdy (one of the weak points on hex363, but the linkage from that to the leg
> piston is pretty weak.
>
> Here is are some pics.
>
> http://www.kclague.net/SSCorpion/P4130047.JPG
> http://www.kclague.net/SSCorpion/P4130048.JPG
>
> http://www.kclague.net/SSCorpion/P4130045.JPG
> http://www.kclague.net/SSCorpion/P4130046.JPG
> http://www.kclague.net/SSCorpion/P4130049.JPG
>
> The force of the sweep is effectively transfered through the hip joint, but the
> force is then transferred to the leg through the leg piston and the leg
> switches. Don't think the 3x5 quarter oval and switch handles are strong enough
> to transfer the sweep force.
>
> Kevin
I can see the good sense in putting the hip switches on their own sets of
levers, as your pics show. That way, the force required for them and for the
legs is independent, so there's no extra load on the switches. I am used to
mounting the switches all in a line on the chassis, especially if there are more
than two.
Have you seen this compressor and regulator (near the bottom of the page)?:
http://www.genuinemodels.com/jcb.htm
This compressor has the pumps at 90 degrees offset by using a V-engine
orientation. It uses 71427 or 43362 motors, which are widely available, and a
good gear ratio has already been achieved. You could crib the design if you use
small compressors or uprate it for large ones, with lower gearing.
You might also see some nice techniques used in the control panel.
(Wow! I wrote less than a page on pneumatics for once!)
Mark
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Message is in Reply To:
 | | Re: SSClagorpion
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| (...) Funny! My presentation at Brickest (classic?) was named Pneumatic Magic. When I started on quad242 I thought the cool thing was going to be the ability to make it modify its behavior to go backwards and turn, but the hardest part was the "no (...) (21 years ago, 16-Apr-04, to lugnet.technic)
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