Monday, January 30, 2012

Perfect T-Shirt Sponsor?

A great guy from a Heavy Metal group contacted me a while ago. Man, I love that music!

They sent a T and a CD, and I can't decide which one I like more. Will wear the shirt when the Hammer meets the Helmet!

Monday, January 23, 2012

"Entropy Slayer 2000": A crossbow to defeat hysteresis

As announced.

Saturday, January 21, 2012

The "Flying Buttress"

A "flying buttress" is a typical element of Gothical Architecture. I read about it first in Ken Follet's great books.

(Here you see a pic of  "Notre Dame" in Paris, France).

The goal of these things is to allow more elegantly designed, lightweight constructions.

I just HAD to bring this lofty idea over to slingshots. Therefore, I made a version of my best design (to date), the "Hammerhead".

I used "Butresses" to stabilize a fork that would be way too thin without this extra support.

This was a very delicate sawying job for sure. But it came out good. Thuja burlwood handle (boy, I missed the smell!), multiplex core. Very solid, even for strong bands.

Here is the orginal design:

Thursday, January 19, 2012

Triumph of the mind (over hysteris)?

Have been thinking a lot about the findings of the thermo cam session. I found out that the hysteris effect (= loss of power when a slingshot band is kept stretched) may be caused by the bands cooling off. The obvious question: What if you heat the bands in stretched condition - wouldn't that bring back the power?

In order to test this, I made a little device that lets me keep a length of band stretched with the fish scales attached to one end. It has to have a hook for the removal of the scales as they switch off after a while, and have to be recalibrated after that. 

It works! Tested this over a few days now. 

- Bands are 30mm x 20mm x 150mm (active length)
- Stretched to 770mm (factor 5,1)
- Have about 4,35 kg initial draw
- Draw goes down quickly to3,25 kg
- Draw stays 3,25 kg for days (same room temperature)
- When heat is applied (with heat gun), the draw can be increased to 4,35 easily
- Bands tear at 4,6 to 5 kg

So it works, the proof is there. The cooling of the bands is the reason for the hysteris, which can be turned around if the bands are re-heated.

The goal: To build a slingshot crossbow that can be kept cocked for days without loosing power.

Bought the heat films today (9 of them for good measure):

These films work on 12V DC, and are listed at 36 W. I plan on making an encapsulated slingshot crossbow (the top can be folded away for cocking the weapon) with several of these films as a heating. A motorcycle battery will provide the power. The front of the slingshot will be closed with brushes so the heated air can not escape.

A switch and a thermometer will be installed as well, of course. Gotta know when it gets too hot.

Interesting tests ahead of us! Stay tuned.

Tuesday, January 17, 2012

New wood on the way

High time to replenish my noble wood stash.

Have ordered these pieces today! Really nice, I am looking forward to the fun of turning these boards into artsie slingshots.

Monday, January 16, 2012

Thermal camera - the video!

Yes, I did make a video yesterday. It was perfect, cold enough to show every detail.

The results are astounding.

These tests also show why the tapered bands typically break about 7 mm in front of the pouch - because that is the hottest part! Obviously the leather pouch cools the band down a bit. The rubber breaks at the hottest point, which stores the most of the energy.

The tests with Destin's high speed cam and this thermal cam help me understanding rubber. Of course it was a known fact that the bands shoot better in warmer conditions, that the bands loose power when you keep them drawn out, that tapered bands tear at the pouch, and that the bands are getting warmer when you draw them out. But now there are explanations. I hope these tests will ultimately help us to make slingshots even better.

Saturday, January 14, 2012

Rubber based air condition?

Further tests are getting more and more interesting.

I took a rubber band (untapered) and stretched the middle part out, then waited until it had cooled down.

Then I relaxed it.

It was COLDER than the room temperature! The first pic shows the retracted band between my hands, the second one the whole band (with the ends beeing warmed from my hands).

This means that you can - in theory - build a fridge (or an air condition) with rubber. Take a slingshot outside, draw it out, wait about 20 seconds, then go with the stretched band back into the house, and let go.

You can build a "Sterling cooler" with this, except that a Sterling normally uses gas and not rubber...

Thermo Camera: First Pictures

The Thermo Cam arrived today. What a great toy!

I tested it with different stuff first, amongst them our christmas tree (which we won't throw out before MariƤ Lichtmess, on the 2nd of February, for reasons of tradition and lazyness).

As you can see the lightbulbs come out very clearly, with 22 centigrade, vs. the tree (around 19 centigrade). See the mirror behind the tree? The lightbulbs are half a degree warmer even in the mirrored image... interesting.

Then I took a few pics of the house.

I left the door open, and you can see the warmth that flows out. You can even see where the heating and the pipes are running (in the second floor, on the front corner).

The camera software allows different colorings (remember it is not recording colors, just temperatures). Here is a different palette:

Then I used it on a tapered rubber strip. First the relaxed picture:

 As you see the rubber has room temperature, whereas my hands have about 23 centigrade.

Then I stretched the rubber... can you see that it heated itself up to about 30 degrees? Warmer than my hand. As expected, the heating was MUCH more dramatic towards the tapered end.

This is sooo much fun.

Thursday, January 12, 2012

New release prototype: A breakthrough?

Tobias is having great success with his "fistgrip" release technique. This made me thinking - is it time for a completely new approach to the release issue?

Made a quick and dirty prototype today with leftover multiplex. I was afraid that it ain't possible to hold the thing together when drawing out, but in fact it is necessary to consciously open your hand!

This opens the door to completely new power dimensions. In most cases, it the the pouch hand, not the arm and shoulder muscles, that determine the draw. This eliminated the need for a strong hand.

And it is soo easy to make. All you need is a bit of wood and a hinge.

I will optimize this over the weekend. An even more canted release angle will allow for a totally relaxed fist position, and even slightly enhance the draw length.

Tuesday, January 10, 2012

New rubber: First bandsets

OK, made a bandset and also tested the draw weight plus thickness.

The 0.02" is really 0,4mm, exactly as thick as TB Black. The 0.025" is 0,6mm, exactly like TB Gold.

So I made two bandsets, one from the thinner material, cut 15,4 (full width) to 9 cm, and one with three times 2,8cm x 1,8cm. Active band length is 28 cm in all cases (full butterfly).

The draw is very close, if not equal to TB.

Can't wait for the weekend!

New rubber - better than Thera Band?

Fetched a parcel from customs today. My close friend Eric (who lives in Boulder/Colorado) sent it to me, as a christmas present! Shipping took forever, so it only just arrived.

This is the rubber from McMaster Carr, a US company. They don't ship to overseas customers, therefore I never had any of the stuff before - except Bill Herriman's "Express Bands", that I tested with great results.

However, I like my bands way heavier, so I needed the raw material. This rubber is absolutely free from any chemicals and is supposed to outperform TB Gold by at least 5%.

I have one 10 yard roll in 0.02" thickness (0,5mm) and one 10 yard roll in 0.025 (0,64mm). 

Can't wait to test it!

Saturday, January 7, 2012

Panther with counterweight

After shooting the "Zombiehammer" slingshot felt so good, I wanted to try a "milder" version of a weighted handheld. 
So I made a modded Panther with a stock turned from European Dogwood (what else). The handle sports a large pommel at the bottom side, which I drilled out and put in a 22mm lead ball. Then I capped the pommel with a bit of leftover olive wood. 

As always, I am thrilled with the density of the dogwood. The way it polishes is astounding, it looks like covered with poly - but it is not. Just buffed up wood. 

Will shoot with it later today!

Thursday, January 5, 2012

Thermographic camera for more "band science"

It is a known fact that slingshot bands convert thermical energy into kinetic energy. If you draw out a band and touch it with your upper lip, you can FEEL it is warm. After the shot, the bands return to normal temperatures.

Physically, the heat is generated by inner friction, but also drawn from the environment (air). When the shot falls, this heat is at least in part given back to the environment.

In order to visualize this effect, I have booked two days with a very expensive thermographic camera, the Jenoptic Varioscan 3021 ST.

Here is the data sheet of the device:

Check out the pdf file

The precision is a fraction of a centigrade (0.03 Kelvin), resolution is 360x240. This should be good enough to show the effect.  Of course, I will use it on tubes, tapered and non tapered flats.

Can't wait! Camera should arrive on the 14th of January.

Wednesday, January 4, 2012

Rightthisminute covers The Slingshot Channel (again)

Watch it here

Draw length extended hammergrip PFS

After I found out that I don't need ANY kind of fork, because of the flipstyle shooting, the next logical step is to make a forkless frame with a draw length extension.

This design retains much of my favorite "hammerhead" handle, and it features a roller on a steel axis.

It shoots really good (as far as I can tell from my tests in the dark, more tests on the weekend).

Tuesday, January 3, 2012

A gift from Ryan Wigglesworth!

I just received a beautiful surprise from Ryan Wigglesworth, one of my esteemed forum members...

What a great natural! Heavily sculpted, just the way I like it. It feels wonderful in my hand. Hard to say what kind of wood that is, could be ash or dogwood.

Thanks, Ryan! A great gift and a wonderful new piece of my collection.