Matthias, your piston&cam mechanism releases the primary release cord when the main sling arm reaches a constant angular velocity, right?

Quote from pancaker on Mar 27^th, 2007, 10:36pm:

 
For this simulation I start the thing running with a constant angular velocity and then just let it run. The release ends up just being timed. Seems to work ok, and the constant KE case seems the easiest to work with for now. What happens during the "snap" is going to be another problem.
 
Both your and Jurek's explanation of the acceleration due to the booster seem on. It's hard to tell what exactly is going on - even with the sumulation all instrumented up. What proportion is due to the outward shifting center and what is due to the tangentially shifting center? What does seem clear from the sim is that the sliding weight seems to "self-tune", which might be the magic trick that makes this whole thing work:
 
For a given weight and length ratio, the secondary release arc is pretty much constant, regardless of speed. The way the sim posted above was configured, you hit max V about 90 degrees after releasing the secondary. You can adjust the arc with either length or weight. How far out the cord the booster runs is also a mass problem - angular speed doesn't look to play. So there are three tools that each tune the three most important aspects of the throw mostly independently, and it just might be possible that one tuning could work through a range of slinging speeds.
 
The tension and handshock issues are a bit funny. The second you drop the pouch, your perceived tension drops way down, before smoothly increasing again up to a maximum when the secondary hits apogee. With a "hard" trigger in place, it looks like a pretty solid tug. The timing gets tricky too.
 
Basically the booster slides out until it has dumped all of its energy. If we're going to use it to trigger a release mechanism, it still needs to be sliding when it hits, so we have an inefficiency as well as the hand shock issue. It's not moving outward too quickly at the end of it's short little run.
 
I think the friction should be manageable as well - except for maybe the first instant, when the sling is folder 180 and sliding quickly. The booster might need some care. Wear isn't likely to be too bad.
 
Maybe Dravonk's release combined with an unrestrained slider would work? Then you'd have a simplish sliding booster and a relatively reliable release... Getting a bit complicated, but I still think there is great potential. Looking at the tensions and timings, I'm still not "quite" convinced that this isn't doable with a manual release. Jurek's sliding weight seems to smooth things out a little, but tragectory control is still going to be tricky.
 
Thanks everyone for playing along!   Just in time for spring.
 
Matthias

Wild idea, this compound sling!  I love original idieas, unlike a lot of other people, apparently!

Better idea.  Simply weight the end of the tube at the closed end.  O = open tube, c = cords attached here, w = closed and weighted tube, p = projectile start point.
 
   OOOOOOOOOOOOPWC
 
This would just replace the pocket and release cord on a standard sling.  I've played with a similar idea, minus weight and with less tube and more cord ( Just a pipe pouch really )  with a view to keeping multiple shots tight.   It worked in one plane, one gets an arc of shot.   So one can certainly cast from a tube.
 
Or for a double whammy, extend the entire thing, add a cord to the open end of the tube, and a second weight on the retention adjecent to the open end ( sling folded ) with another cord extention from the second weight to the hand.  
 
  CCCCCCCCCCCCC.OOOOOOOOOPW.CCCCCCCCCCW.CCCCCCCCC
 
I suppose one could keep adding extensions indefinatly ending up with the deadliest grain of sand ever.  Maybe that part is over the top.  
 
The tube idea may be easier to test if one made it one tube within another, as one could fiddle with length.  

Quote:

 
Matthias,
 
I still see that analogy, not so I'm as obtinate as a mule, I just see it in that way. Of course, thre are some differences and complications, but the principle in both the cases is the same for me. And I think that sometimes it is good to reach stars and planet first. Maybe someday we will reach them with a super-hiper compound sling
 
Jurek

Pancaker,  
 
The pulley example is a very good one. I was thinking of useing a sort of pulley, but it would create problems with the sling orientation during wind-ups. It would be the best solution to reducing the friction on the cord. I don't fear it could be a reason of wear and tear of the cord. A much worse thing is waste of the kinetic energy of the booster mass. As I said before I'm pretty sure the friction is the biggest enemy of efficiency of the sling. The less friction, the better energy transfer.
 
Since Matthias is able to do such excelent simulations, it would be waste of time to do "hand-made" calculations indeed.
 
I love simulators and math results either, but they would be useless without human-brain-intuition simulators, isn't it.  
 
Jurek

Quote from Yurek on Mar 28^th, 2007, 4:47pm:

 
Indeed. Too bad it won't run on your machine Jurek - it's a fun little program, and not too hard to get a handle on. Not to say that actually coming up with virtual mechanical devices that actually DO what you want doesn't require a whole heaping pile of human-brain-intuition! But that part is fun too...
 
Looking at the sliding weight simulation some more, I'm not entirely convinced that friction losses amount to anything. Even if the weight is fixed, as in my original drawing, the energy transfer seems to happen the same, but without the auto-tune benefit. So long as the weight moves smoothly, without jerking it might just work.
 
I've built a prototype... Tennis balls. Included-angle release hook. Sliding booster (possibly highish friction). Maybe if the park is empty this afternoon... I did a low speed "test" in the backyard spinning slowly in a plane around my body and it seems to work perfectly . Small yard... bad idea.
 
I might even go so far as to say that I'm optimistic! My release hook needs beefing up though - I'm not sure if it will handle even the tennis balls with a real throw behind it. I'll start slowly, and see if I can't shoot some video.
 
Matthias