Zed's Technical Writings

Terminal Ballistics - A model to predict penetration depth

Thu, 08 Dec 2011 16:51:00 +0000

Summary

In this blog entry, I use data published by The Slingshot Channel to come up with a simplified formula to predict the depth of penetration of slingshot projectiles in ballistics gelatin. Gelatin has some initial resistance to penetration, but once you get over 20m/s (65fps), you can expect the the projectile to penetration its own...

Comparing slingshot kinetic energy to common ball sports

Thu, 08 Dec 2011 14:15:00 +0000

Summary

In this blog entry I consider how slingshots stack up against other other common human powered sports. I have selected a number of sports that involve a human flinging a ball, from golf to the shotput, from soccer to Jai-alai. Slingshots possess the least kinetic energy of all these sports. They aren't the fastest either....

External Ballistics: Elevation/ Declination

Sat, 03 Dec 2011 08:28:00 +0000

I have previously touched on external ballistics and drop, but as my focus is target shooting and not hunting, I had not made a study of elevation. In this blog entry, I discuss:

Compensation for drop by aiming above the target
How a target that is higher or lower than the shooter affects the flight of the projectile

Please...

Optics

Fri, 02 Dec 2011 13:58:00 +0000

Target shooting glasses

From my discussion thread: http://slingshotforu...ooting-glasses/

I have made some target shooting adjustable iris safety glasses.

Such devices are sometimes used for target shooting disciplines that require iron sights because they...

Analysis of Shooting Form

Thu, 24 Nov 2011 13:20:00 +0000

I have done some further analysis of Jörg's high speed video. It shows Tobias shooting full butterfly, a style which he mastered. I was impressed and intrigued by his form and chose to look at it in more detail.

Here he is at the start of the...

Tapered Flatbands - Mechanism and Effect

Sun, 20 Nov 2011 04:24:00 +0000

My good friend Jörg Sprave has been shooting very high speed video of the release phase of slingshots using the Phantom high speed camera. This shoots high quality video at 1,000 frames per second, allowing him to take calibrated measurements of distance travelled by a projectile over time. He published his data as a chart on his blog...

Effect of temperature on rubber

Mon, 14 Nov 2011 13:55:00 +0000

Why does rubber shoot faster on a hot day and slower on a cold day?

Natural rubber uses heat to contract. The more heat there is, the more it will contract. This can be shown as follows:
If you heat a band under load, it will contract.
Also, its resilience, which is the major input in band efficiency (the difference in the...

Rubber is a maddeningly fascinating thing

Tue, 08 Nov 2011 04:04:00 +0000

Aaron/mods, please don't feature this entry. it's just me thinking out loud to myself to ward off insanity.

Before you start reading, this is not a post full of answers; it's a post full of unanswered questions and conundrums.

We as a sport know surprisingly little about the physics of contracting rubber and there is not much...

Stabilising non-round projectiles

Sun, 30 Oct 2011 10:29:00 +0000

Summary

To summarise, don't try it; it's a fool's errand. Stick to smooth lead or steel round ball if you can.

Disclaimer

Don't do it. It's dangerous and there's no point as far as I can tell. If you ignore my warning and go ahead anyway, you'll...

What's the optimal velocity?

Sat, 29 Oct 2011 09:10:00 +0000

Intuitively, it may seem that we'd want to shoot a slingshot as fast as possible so you don't have to adjust for drop. That's really not what we want. We actually want to shoot reasonably fast. Not slow, but also not crazy fast.

At around 70m/s (230fps), at 10m (about 10 yards) a projectile drops 10cm (4 inches) on the way to...

The flip action

Sat, 29 Oct 2011 05:02:00 +0000

The flip is an important part of the action of a OTF (over the fork) slingshot design.

When the band is under tension, the fork tips provide the anchor point that applies tension and also sets the aim point
When the tension is mostly released, and the projectile is mostly travelling under momentum, it carries the fork out of the way...

User behavior polls

Sun, 23 Oct 2011 08:27:00 +0000

Many of us work somewhat in isolation. If we only read the forums, a few voices tend to dominate the discussion and these tend to be at the extremes. Therefore, I launched a series of polls to get a feel for the forum's general shooting and buying habits. The polls have run for a year, so I think we have enough data to draw some conclusions. I...

Slingshot Knuckling

Tue, 11 Oct 2011 07:56:00 +0000

Abstract:

Over normal target distances, using round metal balls, the effect of spin is almost negligible. Pay it no heed.

However, various factors will increase the effect of spin:
long range
high velocity
off center mass distribution
irregular shape
surface texture
large, low density...

What defines good rubber sheet?

Mon, 15 Aug 2011 10:12:00 +0000

Over the last year I have done quite a bit of band testing. In the end I decided to stick to Thera-band because it is the gold standard, being both durable and fast, but if it's not available locally, you may want to test other exercise bands and medical latex sheet.

Some materials shoot a lot better than others. However, it's easy to tell if a...

Slingshot Guns - summary, ideas and prior art

Sun, 23 Jan 2011 10:18:00 +0000

A slingshot gun is an elastic-powered slingshot that uses a stock and trigger mechanism to increase power and accuracy. In this blog entry, I post some discussion, examples, patents and prior art relating to this topic. I have a fair amount of experience in this subject, following several builds over decades of obsession and it was research of...

Attaching tubes and solids to the fork

Fri, 21 Jan 2011 08:31:00 +0000

I was asked today to help troubleshoot a tube bandset that wore out prematurely by abrading at the left fork tip as it passes through a drilled hole. Tubes are not my area of expertise, but I have hung out on this forum so much that I can pretty much guess what the experts would say. Just in case others who are more experienced may disagree, I...

Cutting out a board cut frame

Mon, 17 Jan 2011 09:04:00 +0000

Introduction

A common question asked by beginners is What's the best way to cut out a board cut slingshot frame? There are many many tools and techniques that can be used to successfully cut out a board cut and that's the reason for this style's great popularity. Anyone can do it with what they have to hand. That said,...

Thoughts on Band Chains

Wed, 12 Jan 2011 09:48:00 +0000

This blog entry encapsulates my earlier forum posts on band chains (link) and some subsequent musings prompted by the recent resurgence of chained bands. It is not meant to be controversial, nor detract from others' writings in support of band chains. Band...

How to adjust band dimensions for different sizes of ball

Wed, 05 Jan 2011 07:55:00 +0000

A friend asked me how to adjust the width of the band to shoot bigger balls. I figure it's a common question that is worth explaining in my blog.

[quote]I've tried the Green TB 21.5cm x 7.5 x 5 set up tonight with 3/4" steel balls. It works fine.

However, I noticed it's too weak with 12mm steel.

Question: what is the better...

How to adjust band dimensions for different colours of Thera-Band

Tue, 04 Jan 2011 11:10:00 +0000

I was asked today why people choose different thicknesses of Thera-band and how to adjust band dimensions.

Why?

Thinner bands shoot slightly faster, especially when they shoot light projectiles, but they don't last as long as thicker bands. I generally don't like anything thinner than Silver and only sometimes Black, but the...

Transitional Ballistics of Slingshots

Thu, 16 Dec 2010 09:15:00 +0000

Executive Summary

The goal is to impart as much kinetic energy as possible to the projectile in a linear manner directly towards the target without imparting enough spin to affect the flight. However the draw and release is the most critical moment that determines the accuracy of the shot. Good slingshot and bandset design and...

Relationship of Draw Length to Velocity

Tue, 14 Dec 2010 13:46:00 +0000

Summary: In this blog entry, I explain the relationship between draw length and both kinetic energy and velocity using charts and a little physics. I go on to simplify the equations to show that:
Increase in kinetic energy is directly proportional to increase in draw length
Increase in velocity is approximately 70% of increase in draw...

Type-Z Pouch Attachment

Tue, 14 Dec 2010 13:35:00 +0000

I have stumbled upon a new way of attaching bands to the pouch. It derives from the way tubular bands are attached.

All you do is:

(1) Make the end like this, with a tiny hole punched or burned through with a hot wire. Ideally the end should be rounded, but it's not critical. For thin elastic, you might double the end over before making ...

External Ballistics of Slingshots

Tue, 14 Dec 2010 03:05:00 +0000

Executive summary: Generally, adjust only for drop. A medium sized (8 to 12mm) lead ball travelling at speeds of around 60 to 100m/s will be the most accurate combination and carries sufficient energy to humanely kill any legal game that I can think of.

Introduction

External ballistics is the science of an...

Terminal Ballistics of Slingshots

Fri, 10 Dec 2010 08:42:00 +0000

Introduction

My slingshots and their bandsets are primarily engineered for maximum accuracy as I believe most of my customers intend to use them to shoot at paper targets. However, I do on occasion hunt with slingshots to fill the pot and I know of various people who have reported success in using them for vermin control.

There is much...

Aesthetics from deep time

Wed, 08 Dec 2010 07:02:00 +0000

Denis Dutton talks about the evolutionary basis of aesthetics.

A link to the video and transcript (link).

[quote]I try to figure out intellectually, philosophically, psychologically, what the...

Slingshot Types

Wed, 08 Dec 2010 06:32:00 +0000

Generally, the grips are:

Hammer grip
High finger grip
Wrist braced grip
Starship
Others

Power; modelling slingshot band velocity and energy (Melchior Menzel's Paper; 2006)

Wed, 08 Dec 2010 04:45:00 +0000

Everyone who has the inclination to try to understand the science of slingshots should read Melchior Menzel's excellent paper Power, a small theoretical approach to understanding and improving slingshot power, 2006...

Discourse on Bandset Design

Mon, 29 Nov 2010 03:41:00 +0000

The following PM discourse between myself and Nico serves as a good primer in bandset engineering.

[color="#006400"][quote name='Nico' timestamp='1290908896']
Hi Z,
I had saved this link about a year ago but have not really given it too much study. It sort of delves into some of your studies. Dont know who wrote it but...

Optimal Projectile Size

Wed, 03 Nov 2010 16:48:00 +0000

I used to shoot BBs (.177 to .22 steel roundball) very fast, but now I realise they are more accurate when slower.

Normally you want a slingshot projectile to fire faster than you can reasonably expect to shoot it. With higher velocity comes a flatter trajectory which is easier to estimate.

However, retardation and spin rises exponentially...

Calculation Resources

Fri, 29 Oct 2010 06:48:00 +0000

I have made available for download some of my calculation spreadsheets.

http://www.l2i.org/s...ot/usefultools/

While I endavour to ensure the correctness of this data and calculations, they are only my own back of the envelope calculations and I accept no responsibility for their...

My Slingshot Topics (Reference Links)

Wed, 27 Oct 2010 07:18:00 +0000

How to Tie Fastbands (Video, Images and Text Instructions)

Tue, 26 Oct 2010 07:29:00 +0000

1. Only use tips with a pronounced tie groove

http://www.l2i.org/F...Fastbands01.jpg

2. Fold Fabric in half around bottom band only

http://www.l2i.org/F...Fastbands02.jpg

[size="4"][b]3. Tightly wrap tie around fork,...

Designing a slingshot frame

Sat, 18 Sep 2010 03:38:00 +0000

Designing a slingshot is easy. In this blog post I will show you my method and then talk about stimulating creativity.

Design Process

The first step is to decide on the slingshot's dynamics. This determines the way that it shoots. It is the most fundamental part of the design process.

[list][*]The...

Pouch designs

Thu, 16 Sep 2010 06:21:00 +0000

In this blog post I will consider some ways we can re-shape the traditional leather pouch so that it shoots faster and lasts longer.

We all want to shoot reasonably fast. Speed gives flatter trajectories and higher impact energy. Ideally, we want to do that without having to pull a lot harder. Some people who may already be shooting tiny...

Leather test results

Thu, 09 Sep 2010 15:02:00 +0000

I am always looking for ways to improve my slingshots. One way is to make the pouch out of an exceptionally strong leather so that it can be made as light as possible. Saving pouch weight can make a substantial difference in velocity, particularly when shooting light projectiles.

I did some research and asked some people I know who are in the...

Mass - Velocity and Kinetic Energy Curves

Sun, 29 Aug 2010 19:13:00 +0000

I have measured and plotted some mass-velocity and mass-kinetic energy curves for my standard bands.

http://www.l2i.org/s...9FB_178_711.jpg http://www.l2i.org/s...9FB_152_711.jpg

http://www.l2i.org/s..._203_864.jpg...

Can bands be too thin?

Wed, 25 Aug 2010 04:09:00 +0000

I've been having problems with an experimental bandset of Thera-band Black. Essentially they are the same formula as my die cut doubled Thera-band Gold bands, but in the thinner Thera-band Black and with a tiny 50mm x 6mm pouch.

I want them as a fast bandet for my little (38lb) daughter. She'll be shooting 6mm steel ball and I've...

Bandsets - Balancing performance with longevity

Sun, 22 Aug 2010 05:10:00 +0000

My first homemade bands were crude affairs. They shot lead balls and I loved them. However, before long. I went off on a quest for the ultimate in velocity and energy. I made some extreme bandsets that pushed the envelope in every direction: lighter, faster, thinner, more tapered. I spent a great deal of time experimenting, designing and...

How does draw strength affect accuracy?

Sun, 08 Aug 2010 17:44:00 +0000

I've known for a while that the heavier I have to pull, the less accurate and consistent my shots are. I've been looking for ways to describe or quantify that, because I want to establish my optimum draw strength for accuracy. By using heavier bands and heavier ammo I should shoot flatter and straighter, but after a certain point,...

Band cutting

Sat, 31 Jul 2010 18:00:00 +0000

I've struggled with band cutting. I currently use a rotary cutter and steel rule on a cutting board and I still have trouble making an accurate cut and getting bands the same width. To make things worse, my latest designs involve not just straights or tapers, but complex curves.

I think I have found a solution, though. I once had some...

Youtube Channel - High Speed Video

Sun, 11 Jul 2010 13:53:00 +0000

I've just signed up a Youtube account (ZDP189HK) to share videos. I'm not competing with Jörg; I'll just post maker tutorials and technical videos there.

Here are three videos to kick off. They were shot in high speed motion capture to illustrate and measure slingshot...

Moralities of copying

Wed, 07 Jul 2010 07:55:00 +0000

We've philosophised a lot about this the morals of this topic in the knife-making community. Just like slingshots, it's a basic technology and most designs have been made similarly by someone at some time in the past and similarly, people are trying to make a a recognisable product and to make some income from it.

There's a whole...

Chinese-style shooting

Sun, 06 Jun 2010 04:41:00 +0000

Yesterday danny came over to view my workshop, drop off a catch bag, frame and some bands I'd bought and teach me a bit about Chinese slingshooting.

I expected to be beat hands-down in accuracy. That I was. No contest.
I expected to trump him in speed and energy. I'm not convinced it...

Compromise and balance

Mon, 31 May 2010 08:58:00 +0000

I've been thinking about how to design the best bandsets for my needs. I'm a target shooter who wants to take a similar bandset out to hunt. I like a chin draw. What works for me might not work for other people, because we're all different. A person's best bandset depends on many factors such as how strong you are, whether you need...

How hard can one pull at different lengths of draw?

Fri, 28 May 2010 17:28:00 +0000

I was wondering about the merits of the butterfly stance compared to a conventional draw length. It seems obvious that if you stretch a band longer it will shoot faster as long as you don't seriously over stretch it in the process. That would imply that the longer your draw stance the better. A full butterfly stance would always trump a chin...

Hysteresis is Sapping Your Energy

Fri, 28 May 2010 05:10:00 +0000

Hysteresis: Sapping Your Energy

Bands snap back with less force than it took to pull them. Latex and other elastics are are not like perfect springs. Some of the energy you put in drawing a band is wasted. It's primarily about internal friction and the energy is dissipated as heat, there's a little tearing going on, and a few other...

Band Failure - Modes of Failure and Prevention

Thu, 27 May 2010 08:37:00 +0000

Over the last week I've had several bands fail on me. That's not uncommon. My bands fail all the time, because it's a fundamental problem with bands and essentially all elastic and it's especially bad in my bands because I have been pushing them to the limit with thin bands and/or aggressive tapers. What's more unusual is that...

Why are tapered bands faster? And what useful information have I learned in the process of discovering the answer?

Tue, 25 May 2010 12:20:00 +0000

My kids are one of my main driving forces. They ask pertinent questions that I might otherwise not think to ask myself and they won't stop till you run out of answers.

Why is the Earth round? Because things stick together and the most efficient shape for a clump is round. Why? Because of gravity. Why? because mass curves...

My new blog

Mon, 24 May 2010 05:59:00 +0000

Hi and welcome. I have decided to create a blog to enter my thoughts about the sport and link to things I have made so that the forum doesn't fill up with the overflow of my hyperactive mind.

Throwing it all out

Mon, 24 May 2010 05:49:00 +0000

I think I've taken the conventional Chinese-gripped, flip shooter as far as I want for now. I've added and trimmed, experimented and embellished, but at the end of the day, it's become all variations on a common theme.

Maybe I'm doing it all wrong. Why do the bands have to come over the top? Why does the draw force work to fold...

Selecting and tuning bands

Mon, 29 Nov 2004 16:00:00 +0000

Picking bands is not unlike buying a car. You can buy a 2-seat sports car with a high state of tune, or a reliable family sedan. Of course, we all picture ourselves behind the wheel of the sportster drifting around mountain roads, but in reality it might not be the best thing for the daily commute or for towing a boat to the lake.

Let's...