Zombie Short Story: Part 2

Here:

http://new.robotsquad.org/forum/viewtopic.php?f=33&t=74290#p1935249

On bands: The Break-In-Effect

In order to further clarify the advantage of tapered bands, I re-watched the slomos done with Destin's camera.

I noticed that the elongation of the rubber close to the pouch was a lot higher than the factor 5,5 (which is the way the band was cut). It was more like 7.

So it seems possible that the extreme overstretching is responsible for the speed advantage, as that does not happen on untapered bands.

In order to test this, I made a stretching stick. I put on a 2cm wide strip of TB Gold and markered the 10 cm length point. Then I attached a hand grip, with a karabiner in order to draw with the scales.

The first interesting finding: TB Gold can be stretched to the factor 8! That is right. But the draw weight increases steeply between 7 and 8.

Second interesting finding: The relaxed length increased. After stretching it out to the 80 cm, the relaxed length was 12 cm instead of 10...

Of course there is hysteris, means, if you keep the rubber drawn out it looses power swiftly. But it recovers, and fast. After 10 minutes, the relaxed length was 11 cm.

Third finding: Stretching the rubber that far breaks it in, means, changes it forever. The rubber did not go back to 10 cm. It stayed at 11, even after a few hours.

Fourth finding. Once broken in (stretched out to 80 cm and held there a bit), the rubber permanently looses draw weight.

See the attached graph - after the break in, 80 cm draw can be achieved with the draw weight needed for just 70 cm in unbroken in condition.

What does this mean? Well, the next experiment must be to cut a much shorter and thinner band set than usual, without tapering, that can be stretched to factor 8. The chrony will tell what the effect will be.

Great fun at the "Basement Tournament" again

Last Saturday night, I participated (for the third time) at Tobias's basement tournament. I fetched Wladimir (aka "9Gramm") in Nuremburg, not much of a detour from my home.

Wladimir is a well know shooter, he participated for the first time.

As always, the fun started with a great dinner. Homemade "Fleischkäse" (meat loaf) and "Nudelsalat" (pasta salad) plus the last bottles of the homemade beer Tobias and Jochen sometimes brew! Excellent.

Then the shooting started. The setup is hard to beat, a 300years plus old rock basement, well heated so the bands have great performance. The current shooter is in the neighboring room, the others sit on armchairs in a protected corner with great view of the target.

The disciplines had been well thought out, as always. A great mix of precision target shooting and destruction! We had to shoot a golf ball off the neck of a beer bottle, with minus points when the bottle got damaged... and we had to destroy three beer bottles that stood behind a thick particle board. You had to destroy the board first...

Tobias won, with just a few points between him and Wladimir. Actually, I think Wladimir had one beer too much, at a strategically important point. He shoots 10 mm steel balls at blazing speed (full butterfly bands). A lot of velocity, but not much impact! He had to hit the particle board at least three times at the same spot to crash through the board, but he failed. Tobias (20mm steel) and myself (25mm steel) had no such problems. In fact, I had destroyed all three bottles after three shots, and the remaining seven weren't needed.

Wladimir paced the beers better afterwards, and his groups got more tight again.

I came out number four, not so bad if you keep in mind my hand is still not fully recovered. Just three weeks earlier, I hit it with a 25mm steel ball from the rooftop slingshot... I was lucky.

When the tournament part was over, we switched to the destruction part. Tobias had an old printer and a radio. We smashed it into pieces! Then Jochen, who is a butcher by profession, brought some cattle bones. Man, those are something - looks like Dinosaurs to me. The 25 mm steel smashed through the shoulder blade easily, and even cracked the cow thighbone.

We went to bed at four in the morning, exhausted but happy.

What a great way to spend Saturday night! I brought Wladimir back home, and his wonderfull wife has prepared a fantastic breakfast. When I got back home, I went straight to bed for a nice nap, well fed and happy.

ECST 500 Dollars Slingshot Arrived!

I am sooo glad.

Another impossible slingshot

I know what people will say once I show off the hammerhead frames. "You will hit your hand". I know the fork is low, but of course I won't hit my hand with it.

The rooftop slingshot, a far more dangerous design, really hit my hand. Or, rather, I did, not using it correctly.

But a normal fork is a different issue. In order to show the safety, I made a version of the hammerhead that has a 40mm "wall" above my hand. The fork is only 25mm high! So it seems impossible that the ball can fly over the wall.

And yet it works. Flipping does that. The safety margin is a good 100mm.

Will show it in a video soon!

Who needs science?

 I have received lots of praise, but also some negative comments about my latest video.

People said that is shows the effect of tapered bands, but that it does not explain the fact, and it does not say how a better band can be derived from it.

Of course the video does not explain what happens, simply because we don't know yet. But it provides reliable data for those who want to explore the issue. This data was not available beforehand. Destin (who is a rocket scientist) has given the data to his professors, and they say they want to find out what is going on... it is clearly a challenge for these guys now.That's fantastic!

Dan has used the video intensively to study various effects. I find it quite fascinating.

Read his blog entry here

Science works that way. I can only contribute to the solution, not provide it.

One of my other fields of interest is the history of contagious diseases. When the first microscopes came out, scientists had been able to see the bacteria and viruses for the first time. Fascinating. but it was useless at first, as seeing what was going on did not mean that a cure was immediately available. But it enabled other scientists to come up with vaccination and effective treatments.Microbiology ultimately found cures for some of the worst killers in the history of mankind.

My little video won't save lives of course, but I believe that it will ultimately lead to better slingshots.Science works that way.

Having said that, witch doctors are still in business today, trying to cure cancer with goat poop and stuff! I guess that likewise, some guys will always insist that office rubber bands is all you ever need to make a good slingshot. Which is fine, if you don't care for progress.

First slingshot after the accident

OK, after 16 days my hand is healed enough for some light slingshot making. Boy, have I missed my workshop!

I used some moor oak leftovers and some plywood, made a new variation on the Hammerhead. Slightly smaller fork tips (18mm dia, so they can be made from the single multiplex board), a slightly thicker "throat" so the pressure on the webbing between index finger and thumb is distributed better, and a "butt tail" at the rear lower end.

I feels really good in the hand, but I need to do some shooting to streamline it. Too bad there is so little daylight now, it is dark when I come home from work.

Finally.

 

Pop! Goes the champagne bottle :)

Slingshot Bands Demystified

Thanks to Destin, finally, at last, answers. Here:

New video is online!

Tapered vs. Straight - Reliable Data

I have analyzed the first high speed recordings.

Two bands with identical length and identical draw weights. Double TB Gold, full butterfly, one cut 2,8cm x 1,8cm, and the other one 2,3cm straight.

As you can see, the tapered band was immediately faster than the untapered one, and it also accelerated longer. The straight band reached the peak speed of 69m/s at frame number 26, at 101,6cm. The tapered band set reached the peak speed of 79 m/s at frame 24, at 116 cm.

The rest of the flight added no more acceleration, even though the ball stayed in the pouch in both cases. Quite interesting!

A great Sunday!

I picked up Destin in Karlsruhe and we drove to Tobias's farm, just 30 minutes away. The sky was still overcast, not great for the high speed camera... but it was bound to clear up later on.

We set the equipment up - wow, what a camera! A "Phantom", made by the US company Vision Research.

A 1000 frames per second at 1280x720 resolution (HD)! I don't really know how much this beauty costs - but I am sure it is worth every penny.

Check it out on the manufacturer's website

It cleared up right on time, and we did many great shots... smashing particle boards... smashing pumpkins... smashing three pumpkins in a row with the big cannon...

We also did the test that was suggested here, with "striped" bands. I cut three bands, one untapered, one with a decent 2:3 tapering, and one with a very aggressive 1:5 tapering. Tobias did the shots in full butterfly, the footage is frontal.

I will now be able to draw up an accel curve of the ball in the pouch. This can hopefully shed some light into the dynamics of tapered bands.

Arrived back long after nidnight... will edit the first video tonite, hopefully.

Guest star for the next video

On Sunday, I will be doing a video with another great youtuber, Dustin from Huntsville/USA.

He runs an excellent youtube channel called "Get smarter every day". Here:

http://www.youtube.com/user/destinws2#p/u/2/_eUlpPY96Ok

Destin will bring his fantastic HD slomo camera, and we will do a lot of tests. Hopefully the image quality will be much higher in comparison to my cheap little Casio. 

We will meet at Tobias's farm, because I need another weeks rest for the hand. Tobias was so kind to be my substitute for the tests! So we will film the current record holder for the strongest handheld slingshot in action, in brilliant HD quality.

Can't wait!

More coverage on German IPTV

I love publicity... gotta admit it. :)

A few days ago, I got interviewed by FocusTV, the online presence of a popular German news magazine. Came out quite good!

One step closer to my goal, an own TV show...


Watch the video here (German audio, sorry)

Slowly Healing

Well, the healing is in progress.

Here you can see how the wound looks like today. It is clear now that the ball hit the top of my hand, squeezed skin and flesh until a tear opened, then it ripped a "pouch" into the back of my hand and flew on.

Can you imagine what would have happened if I would have gotten a full hit, to the root of my thumb?

Blood and Pain

Well, here is the video with a bit more "blood" pics, and three new slingshots.

Accidents...

can happen if you are getting careless.

As I was today. Wanted to Chrony my rooftop slingshot, and focussed too much on not hitting the equipment... so I hit my hand instead. With a 1" steel ball. The same that  goes through 40mm particle boards.

It got deflected, and still hit the catch box with enough force to topple it over. But it also wounded my hand, very significantly. Here you see my "flight path" to the bathroom, to pour some water over the hand.

My wife says I need stitches. I don't think so, it is just a deep nasty cut. But I better listen - this time.

490 shots today, from 14 meters.

In order to test the new "Hammerhead" design, I banded it up with double TB gold bands, 2,8cm x 1,8cm x 32cm (active band length 30cm).

Started with 15 mm steel balls and shot at air rifle paper targets. Drew out full butterfly, but that was too much energy for the 15mm steel, and I got nasty handslaps. Band teared after 112 shots. I repaired it by shortening, 27cm active band length. Drew out less far, to avoid the handslaps.This lead to far better band life.

After 340 shots with the 15mm steel, I had enough. The back side of my pinkie and ring finger was swollen and raw, from the handslaps. I switched to 19 mm lead, and used empty cat food cans as hanging targets. No more handslaps!

I drew out to max again, and after a total of 392 shots, I had to shorten the bands again. Now I am at 490 shots total, and the bands are totally intact. Not bad!

The frame shoots like a dream. Actually, my pouch hand is a lot more stressed out than my fork hand.

Went through several cardboard pieces, and paper targets. Here is the result of 490 hits!

Test shooting session tomorrow

As you may know, I think I will send the "Hammerhead" to Pete Hogan to get it cast in aluminum and bronze.

Before I do this, I want to follow Tobias's suggestion and try the heck out of it. So I cut three brand new bandsets, two layers of TB gold, full butterfly. 12 kg of a draw (26 lbs). I will go through all of these bands tomorrow, many shots. Then I will know if the design is any good.

Hammerhead: Fine tuning

Have enhanced the handle a bit, made it thinner and shorter. This is IT now! I believe this is the best hammer grip frame I ever made. I am thinking about sending it to Pete Hogan to get it done in aluminum or bronze.

The Hammerhead - new design

 I talked to Tobias, fellow slingshooter and the current record holder for the most powerful handheld discipline, about further enhancing the available designs for hammer grip shooters.

We both use my "Hand Howitzer", which is a great slingshot. However, the "Lead Launcher" is also a good concept. And two of my other frames have advantages, too. So we spent some time thinking about how we can "marry" all these designs.

Here is my take!

The fork is low, which is achieved by making the "throat" very thin - but deep. This way, it is totally solid and won't ever break under stress. It thickens out to a 20 mm round tip, for easy band attachment. The handle is very narrow right under the fork, which is great for holding the frame in the webbing of the hand. A huge palmswell gives you fantastic purchase, and the curved front of the handle is from the "lead launcher" design - very effective. 

I started out with three identical forks, cut from 18mm Multiplex.

Rasp work done.

File work done.

Totally flat over the hand.

Banded up with three layers of TB Gold, very powerful - but manageable with this great frame.

Here you see it next to the three other models that influenced it.

Hope you like it!