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Understanding The Physics of Slingshots


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#21 busySteve

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Posted 18 May 2016 - 04:46 AM

 

Well, I just received the force sensor and driver board that will be used for the band measuring project. Next, I have to select a robotic motor for the band stretcher. If this is too far from a slingshot post let me know and I will be more reserved with the progress of this project.

gallery_11160_2175_246127.png


Hi Steve,

I've been tinkering around a bit with Arduino myself recently. Just a newbie side hobby and never imagined applying it to slingshots (got a pretty spiff binary clock in the works at the moment though!). This is very cool. Really looking forward to your next update!

Happen to have a link to the force sensor you bought?

 

 

The aluminum bar looking thing is the actual sensor, sometime called a load sensor.  The one here is 1kg max and was purchased on amazon with the driver board for $18.95, I am thinking I'll be using a 10kg sensor instead, otherwise I'll use leverage to reduce the load of the slingshot rubber by 10x.  I'll post the arduino software I write and the supporting libraries I used to test it on GitHub and provide links if you plan on using one.  

 

Here's the link to the sensor kit:

http://www.amazon.co...ailpage_o00_s00

 

Here's a link to my github for reference, but the code has not been posted yet:

https://github.com/busysteve



#22 Jeb

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Posted 18 May 2016 - 05:09 PM

Cool. Thanks s bunch for that, Steve.

#23 busySteve

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Posted 24 May 2016 - 12:33 AM

I received the 10kg sensor in the mail and hooked it up today.  Works as expected.  I started prototyping the software for the unit and will provided feature details when I demonstrate in a video.  I have decided to use a windshield wiper motor to drive the band stretcher as suggested by my brother in law.  I have an order of pure natural latex on the way too from rubbersheetroll.com.  I ordered .030", .040", and .050" thick sheets.  I will be comparing these bands with Theraband Gold, Silver, and Black.  I plan to provide graphs of all data gathered.  I'll share images and attach spreadsheets.  However, the main goal is to build an accurate rubber calculator page to share with all, and be challenged by it.  I have made some minor changes to the calculator page but it has a long way to go.  

 

For some reason I thought Joules and FPE were the same thing... but learned otherwise.  The site now shows both Joules and FPE.  I am also working on making it metric or US compatible.  Thanks for following along.

 

http://busysteve.com...gshot_calc.html



#24 busySteve

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Posted 13 June 2016 - 09:14 AM

Window motor for band stretcher

 

I finally received an electric window motor.  I will resume progress this week on the band stretcher tension measuring project.  Thanks for your patience.  



#25 Greyman

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Posted 13 June 2016 - 10:11 AM

I finally received an electric window motor.  I will resume progress this week on the band stretcher tension measuring project.  Thanks for your patience.



#26 aiping

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Posted 14 June 2016 - 02:49 PM

@busysteve:

what's about the approach
energy transmittion is optimized when the impedance
of the source is equal to the impedance of the sink

Something (rubber coefficient) x (taper coefficient) x (draw length) x (draw weight) = projectile weight

#27 aiping

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Posted 14 June 2016 - 09:56 PM

Man, I  was tired when I wrote that...

 

What I mean, can it be as simple as that:

 

weight of the rubber bands = weight of the ammo (considering the weight of the pouch and pouch fixing 1/10

(or less) of the ammo)

 

That does not mean maximum speed, but it should transfer optimum energy out from the rubber into the ammo.

Like this click-clack steel pendulum:

 

https://en.wikipedia...Newton's_cradle



#28 busySteve

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Posted 15 June 2016 - 04:29 AM

Man, I  was tired when I wrote that...

 

What I mean, can it be as simple as that:

 

weight of the rubber bands = weight of the ammo (considering the weight of the pouch and pouch fixing 1/10

(or less) of the ammo)

 

That does not mean maximum speed, but it should transfer optimum energy out from the rubber into the ammo.

Like this click-clack steel pendulum:

 

https://en.wikipedia...Newton's_cradle

 

Great point!  This assumes energy transfer is the goal.  Many times the goal is maximum energy(for Power Rangers) or penetration(not transfer) for hunters.  But even if optimal transfer is the goal... how do you band your fork?  How far do you pull back on the rubber for your given ammo mass?

 

The band stretcher is for measuring the stretch and retraction characteristics of differing types and cuts of rubber.  To remove yet another unknown from the list.  Remember, not all rubber is the same.  Inner tubes stretch differently than pure latex which stretch differently than synthetics.  Unless you know these differences it is less like you will be able to predict or guesstimate the outcome.



#29 aiping

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Posted 15 June 2016 - 05:44 AM

Sure! Predicting the energy outcome by given information of the rubber type, banding, fork width!, taper, draw length, draw retention, ambient temperature, humidity, ammo mass, density and shape, (plus band lifetime..) , such an application would be the holy grale. Do it, please!

#30 aiping

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Posted 15 June 2016 - 07:02 PM

to busySteve: This now is OT, but you have the technical background to verify my information, and if so spread it in your technical network. Here we go:

Warning: log_other_mode (Android)

This file is not only grewing by time and stealing precious
internal memory.

This file, when erased to the bone of 4 kB, is growing, when the Android
device is SWITCHED OFF. As long stwitched off, as bigger, proportionally!

For example I switched off after erasing 'log_other_mode' at 3:10 and switched on at 7:15, in this time it grew up to whopping 15.9 MB.

Growing proportionally within SWITCH OFF time makes only one sense:

The Android device monitors with its MICRO the surrounding OF YOUR HOME and SAFE THE SOUNDFILE in log_other_mode. From there it
can than sneak out when ONLINE.

Switched off, the Android device must be completly inactive, but its not!

You can check it by your own:
- root the Android device if it is not already
- install DiskUsage
- go into [root required] /data

NOW: WHO IS INTERESTED IN YOUR CONVERSATION WHEN YOUR ANDROID DEVICE IS SWITCHED OFF

#31 aiping

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Posted 15 June 2016 - 07:26 PM

Add:

If you want to verify my claim, this is also important:

I modified the two! micros of my Android device in a way that they are generating continously 'white noise'.

So you check it in this way:

Erase log_other_mode to the bone of 4kB, switch off (preferable when you go to sleep) and put it beside a continous sound source. When you wake up switch on OFFLINE , than check the size of log_other_mode.

The next evening you repeat that but cover it under a pile of cloth(and don't forget where you put it!)

#32 busySteve

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Posted 19 June 2016 - 07:22 PM

The initial prototype of the Band Stretcher is underway.  I have built the basic platform of plywood.  There is a flat base and a sled that holds the slingshot as it is slid away from the load sensor, in turn stretching the band(s).  The load sensor is held be an anchor point.  The software is not near ready.  I also need to build the H-Bridge driver circuit for the window motor from four 3055 power transistors.  That will probably be the next photo posted.  Here's what I have built so far:

 

 

Band Strether Full View
 
Electric Window Motor With a Fishing Reel Spool Attached
 
The Slingshot Fork Sled
 
Load Sensor and Pouch Hook


#33 busySteve

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Posted 19 June 2016 - 07:27 PM

to busySteve: This now is OT, but you have the technical background to verify my information, and if so spread it in your technical network. Here we go:

Warning: log_other_mode (Android)

This file is not only grewing by time and stealing precious
internal memory.

This file, when erased to the bone of 4 kB, is growing, when the Android
device is SWITCHED OFF. As long stwitched off, as bigger, proportionally!

For example I switched off after erasing 'log_other_mode' at 3:10 and switched on at 7:15, in this time it grew up to whopping 15.9 MB.

Growing proportionally within SWITCH OFF time makes only one sense:

The Android device monitors with its MICRO the surrounding OF YOUR HOME and SAFE THE SOUNDFILE in log_other_mode. From there it
can than sneak out when ONLINE.

Switched off, the Android device must be completly inactive, but its not!

You can check it by your own:
- root the Android device if it is not already
- install DiskUsage
- go into [root required] /data

NOW: WHO IS INTERESTED IN YOUR CONVERSATION WHEN YOUR ANDROID DEVICE IS SWITCHED OFF

 

Sorry, I am not an Android expert.  I suggest you seek Android assistance on Android forums.



#34 aiping

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Posted 23 June 2016 - 05:32 PM

Dear BusySteve,

here are some links which are may be helpfull for
you to develope the Wholy Grale:

https://m.youtube.co...h?v=4Yg9RjauzY0

http://slingshot-sho...ce/science.html

#35 busySteve

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Posted 24 June 2016 - 03:42 PM

This is very good information. Thank you.

#36 aiping

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Posted 26 June 2016 - 05:50 PM

thanks :-)

here what I posted in 'The quest of A-Ping..'
but I think it fits also in your thread:

About rubber science, the higher speed of thinner and tapered bands I
have my own explanation:

- as thin as fast=> the band consists of single molucular springs. These
tiny springs are orientated randomly, but some of them are alligned
in stretch direction. These orientated springs are the most efficient,
the others pointed in worst case 90 degree to the stretch is dumb weight. Imagine, what is 'thin' for our eyes, but the elastic molecule
is some nanometer, a hair is for example about 100.000 nanometer.
So I think, the process to produce thin bands alignes more efficient molecules than dumb molecules as the process for thick bands. If you could manage to align ALL molecules into stretch direction by for example applying a magnetic or electric field, that would be a superband and probably very resistant to rupture.

- fast taper
=> first, I think its all about direction of the force vectors, if
you focus the force vectors (taper) to one point you are most efficient, like a lense. A taper 1/0 is the perfect focus, but band life time...
=> second, taper cut off / eliminates the unefficient/non focused band area so reduces weight, which does not need to be accelerated

#37 busySteve

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Posted 27 June 2016 - 05:14 AM

thanks :-)

here what I posted in 'The quest of A-Ping..'
but I think it fits also in your thread:

About rubber science, the higher speed of thinner and tapered bands I
have my own explanation:

- as thin as fast=> the band consists of single molucular springs. These
tiny springs are orientated randomly, but some of them are alligned
in stretch direction. These orientated springs are the most efficient,
the others pointed in worst case 90 degree to the stretch is dumb weight. Imagine, what is 'thin' for our eyes, but the elastic molecule
is some nanometer, a hair is for example about 100.000 nanometer.
So I think, the process to produce thin bands alignes more efficient molecules than dumb molecules as the process for thick bands. If you could manage to align ALL molecules into stretch direction by for example applying a magnetic or electric field, that would be a superband and probably very resistant to rupture.

- fast taper
=> first, I think its all about direction of the force vectors, if
you focus the force vectors (taper) to one point you are most efficient, like a lense. A taper 1/0 is the perfect focus, but band life time...
=> second, taper cut off / eliminates the unefficient/non focused band area so reduces weight, which does not need to be accelerated

 

This is pretty intense.  I will not claim to understand it much either.  I know more about physical measurements and experimentation than I do about theory.  When it comes to nanometers... that's in the theory realm for me.  :-)



#38 busySteve

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Posted 27 June 2016 - 05:21 AM

I built the first H-Bridge circuit this weekend of MJE3055 power transistors and no-go.  The circuit did not supply enough current to drive the motor that stretches the bands so I may need to build it with power MOSFETs.  I'll be ordering MOSFETs today. 


Edited by busySteve, 27 June 2016 - 05:26 AM.


#39 busySteve

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Posted 01 July 2016 - 07:17 AM

The MOSFET hbridge didnt work either.  Too much current draw.

 

basicmosfethbridge.gif

 

I just ordered a relay pack with next day shipping. That will work for sure.

 

https://www.amazon.c...duct/B00KTEN3TM

 

I'll continue to keep ya'll posted.



#40 woshiqinkaixin

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Posted 14 October 2016 - 08:17 PM

helpful, thanks!






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