Noob possum got pwned by avo cannon

[moT]

I shot a possom out of a tree last week with my home made avo cannon it died.. I am also trying to figure out the velocity of the avocado when it is shot theres a method of doing this by takeing the weight of the avo and the weight of a block of wood which is suspended by 2 strings then by shooting the block measureing the angle of displacement of the block hence work out the momentum and velocity of the avo. im not 100% sure on the process could someone explain

[GIXser]

Wtf.............

[moT]

comon ppl i need to know

[nodrog]

bring it to the pub on thursday, you stand at the other end of the car park with a stopwatch, when you yell "go" i will shoot it at you, you can work out the velocity using the time it takes for you wake up.

and whats with an "avo" cannon? thats so metrosexual, eddie using that shit for a facial scrub.

real men use spud guns.

[Goblin]

Go get some english lessons.

[moT]

bring it to the pub on thursday, you stand at the other end of the car park with a stopwatch, when you yell "go" i will shoot it at you, you can work out the velocity using the time it takes for you wake up.

and whats with an "avo" cannon? thats so metrosexual, eddie using that shit for a facial scrub.

real men use spud guns.

thats 1 method but very unreliable as there is human error, i found that avocados are a perfect fit and are in plentiful supply where i live, potatos i have to go down to food town

[Gubb]

Potato Cannon FTW!

[moT]

Go get some english lessons.

Go get some physics lessons.

[moT]

there has to be someone here better at maths than i am

[nodrog]

there has to be someone here better at maths than i am

no, but theres plenty better at spelling :bleh:

[moT]

Potato Cannon FTW!

FTW? Free The Whales??

[Mikkel]

How precise do you need your measurement to be?

[moT]

no, but theres plenty better at spelling :bleh:

maths is by far the more universal language

[moT]

How precise do you need your measurement to be?

rough estimate as there will be vairiation between shots as weigt of shot changes, air/fuel mix changes. so i propably will do the process a few times to get a average FPS might be worth doing a R(squared) regression

[chrisso]

Very interestng...hmmm got any pics of this Avo cannon?. Ive got a Possum in my roof & as im a Kiwi i reckon im allowed to kill the fucker.Stupid animals are pr:devil2:otected here. Would said weapon work on Rabbits too?

[Mikkel]

You need to be fairly precise in your experimental setup - but yes, you are able to roughly determine the velocity (at the time of impact) by measuring the angular deflection of an object with a known mass.

You'd use two wires to keep said mass rotate around a single axis. If you could precisely measure an arbitrary deflection (regardless of both magnitude and direction) a single wire would be adequate.

[Goblin]

I shot a possom out of a tree last week with my home made avo cannon it died...


no, but theres plenty better at spelling :bleh:It's not so much the speeling, it's the punctuation...or the lack of. Did the avo cannon die?

[moT]

Very interestng...hmmm got any pics of this Avo cannon?. Ive got a Possum in my roof & as im a Kiwi i reckon im allowed to kill the fucker.Stupid animals are pr:devil2:otected here. Would said weapon work on Rabbits too?

yer i can post some up im in the process of makeing a bolt acton spud gun too.. If you want to increast the killing power hammer a big nail right thru the avo/potato or whatever

[Mikkel]

The simplest way of making a rough estimate would be to consider the problem from an energy conservation perspective.

The increase in potential energy of your pendulum should be equal the decrease in kinetic energy of the projectile:

dEkin + dEpot = 0

This is pretty rough since some energy will be expended deforming your projectile, localised heating, wind resistance, non-perfect wires, etc.

dEpot = (m+M)*g*dh - where m is the mass of the projectile, M the mass of the pendulum, g the gravitational constant and dh the change in height of the pendulum.

dh = l * cos(theta) - where l is the length of the wire and theta is the deflection angle.

The velocity should then be given by:

v = sqrt(2*(m+M)*g*l*cos(theta)/m)

:D

It's important that you choose the weight of the pendulum carefully in relation to the weight of the projectile. It is also important that the entire projectile moves with pendulum. You need to establish the centre of mass of the pendulum fairly precisely - or use a very long wire.

[Colapop]

Why don't you just post up the whole method of how to make one? With diagrams. And youtube links of it in action. And the police report....? :cool:

[ManDownUnder]

yer i can post some up im in the process of makeing a bolt acton spud gun too.. If you want to increast the killing power hammer a big nail right thru the avo/potato or whatever

Am I the first the raise the requirement for a firearms license...?

As for the velocity, set the thing up to any angle (I'd choose 45 degrees giving max range), fire it, measure the range then click here (http://hyperphysics.phy-astr.gsu.edu/Hbase/traj.html#tra13)

[nodrog]

Why don't you just post up the whole method of how to make one? With diagrams. And youtube links of it in action. And the police report....? :cool:

google is your friend (http://dangerouslyfun.com/spud-gun) :bleh:

a electric bbq igniter is all i used in mine

[Mikkel]

As for the velocity, set the thing up to any angle (I'd choose 45 degrees giving max range), fire it, measure the range then click here (http://hyperphysics.phy-astr.gsu.edu/Hbase/traj.html#tra13)

Nice - but it doesn't take wind resistance into account. If the firing range is decent then the error on that calculation will be significant.

Having half a metre between the muzzle and the pendulum would pretty much give you the muzzle velocity - with less error. The measuring is a bit more difficult though.

[raftn]

The title had me confused.......from then on its all been down hill.

[ManDownUnder]

Nice - but it doesn't take wind resistance into account. If the firing range is decent then the error on that calculation will be significant.

Having half a metre between the muzzle and the pendulum would pretty much give you the muzzle velocity - with less error. The measuring is a bit more difficult though.

I think close enough is probably good enough on this one... unless ultra long range stuff is going to be done. Avo vs. shipping might be interesting - even turn the tide in Iraq!

AVOCADO OIL!

[Mikkel]

I think close enough is probably good enough on this one... unless ultra long range stuff is going to be done. Avo vs. shipping might be interesting - even turn the tide in Iraq!

I'm more concerned with the terrorist applications of these weapons. They can be made with x-ray transparent materials and smuggling on aboard a plane should be possible... :shit:

:rofl:

[007XX]

Meh who gives a hoot!!! Let's shoot some things....yyeeeaahhhhaaaa!!! :2thumbsup

*sorry, inner redneck popping up every once in a while*

Eh Tom, make sure to post some pics of the result...please!

[moT]

The simplest way of making a rough estimate would be to consider the problem from an energy conservation perspective.

The increase in potential energy of your pendulum should be equal the decrease in kinetic energy of the projectile:

dEkin + dEpot = 0

This is pretty rough since some energy will be expended deforming your projectile, localised heating, wind resistance, non-perfect wires, etc.

dEpot = (m+M)*g*dh - where m is the mass of the projectile, M the mass of the pendulum, g the gravitational constant and dh the change in height of the pendulum.

dh = l * cos(theta) - where l is the length of the wire and theta is the deflection angle.

The velocity should then be given by:

v = sqrt(2*(m+M)*g*l*cos(theta)/m)

:D

It's important that you choose the weight of the pendulum carefully in relation to the weight of the projectile. It is also important that the entire projectile moves with pendulum. You need to establish the centre of mass of the pendulum fairly precisely - or use a very long wire.

thats great i was wondering how the length of the wire was going to factor into it that was my biggest problem

[avgas]

Nice - but it doesn't take wind resistance into account. If the firing range is decent then the error on that calculation will be significant.
Come one Mikkel its not like you to overlook anything.
Yes doing the parabola test has fail in it - but not due to wind resistance - due to fact that it gives you average speed.
Also shooting a avo into a bit of wood wont tell you speed if the wood spins, as the avo will deform loosing most of the energy.
If you want the best calculaiton your going to have to time between 2 points.
i.e. end of barrel to some distance that can be timed and is not too long.
If you were really cheaky you could put 2 sensors in your gun. average the speed down the barrel.

[BMW_RACER]

Fire it directly up, measure how long it takes to hit the ground, apply maths ?!

[moT]

Nice - but it doesn't take wind resistance into account. If the firing range is decent then the error on that calculation will be significant.

Having half a metre between the muzzle and the pendulum would pretty much give you the muzzle velocity - with less error. The measuring is a bit more difficult though.

i agree there is too much error doing it your way the only way i will find a fairly accurate mussle velocity is shooting the block

[moT]

I'm more concerned with the terrorist applications of these weapons. They can be made with x-ray transparent materials and smuggling on aboard a plane should be possible... :shit:

:rofl:

hmmm very true

[BMW_RACER]

i agree there is too much error doing it your way the only way i will find a fairly accurate mussle velocity is shooting the block

Or you could just use a chronograph.

[moT]

The simplest way of making a rough estimate would be to consider the problem from an energy conservation perspective.

The increase in potential energy of your pendulum should be equal the decrease in kinetic energy of the projectile:

dEkin + dEpot = 0

This is pretty rough since some energy will be expended deforming your projectile, localised heating, wind resistance, non-perfect wires, etc.

dEpot = (m+M)*g*dh - where m is the mass of the projectile, M the mass of the pendulum, g the gravitational constant and dh the change in height of the pendulum.

dh = l * cos(theta) - where l is the length of the wire and theta is the deflection angle.

The velocity should then be given by:

v = sqrt(2*(m+M)*g*l*cos(theta)/m)

:D

It's important that you choose the weight of the pendulum carefully in relation to the weight of the projectile. It is also important that the entire projectile moves with pendulum. You need to establish the centre of mass of the pendulum fairly precisely - or use a very long wire.

And is mass in g or kg

[chrisso]

Are we talking your standard Avo or the Hi power Magnum Avo round?;)

[moT]

Are we talking your standard Avo or the Hi power Magnum Avo round?;)

high power unripe avo round

[Skunk]

Pretty simple things. This one is Lynx powered.

Best barrel to chamber volume is 1:1.5

[Forest]

Wouldn't it be more fun just to eat the avocado?

Mmmmmm. Avocados on toast. :woohoo:

[moT]

photos of current one and project bolt action cannon

[moT]

Wouldn't it be more fun just to eat the avocado?

Mmmmmm. Avocados on toast. :woohoo:

yer there nice but its more fun shooting them

[Mikkel]

Come one Mikkel its not like you to overlook anything.
Yes doing the parabola test has fail in it - but not due to wind resistance - due to fact that it gives you average speed.
Also shooting a avo into a bit of wood wont tell you speed if the wood spins, as the avo will deform loosing most of the energy.
If you want the best calculaiton your going to have to time between 2 points.
i.e. end of barrel to some distance that can be timed and is not too long.
If you were really cheaky you could put 2 sensors in your gun. average the speed down the barrel.

Nope - the parabola calculation should provide you with the starting velocity, not the average. You don't directly measure the time it takes before the projectile touches down again - measure how far horizontally the projectile travels inside the timespan it takes for the projectile to reach the apex and return to the ground.
However you expect the ballistic profile to be a perfect parabola and it is not, due to wind resistance. Actually BMW_RACER has the essence of the parabola experiement sorted in the below quote - but that approach is not viable when using explosive shells or if you lack a precise stopwatch.

The reason I did not suggest the timing approach to measuring the muzzle velocity was quite simply that it is much more technical to do precisely. You need an electronic data logger and two sensors to respectively start and stop the logger.

Having a two point pivot on the pendulum using two wires could be sorted out in a way that would prevent spinning. The avocado will always deform, unless it's a crappy cannon - and there will be an energy loss there. It is imperative that all the avocado fragments are collected and swings with the pendulum, then the impact characteristics (bouncy or squashy) shouldn't matter.

If you have access to the right gear measuring muzzle velocity is both simple and precise.


Fire it directly up, measure how long it takes to hit the ground, apply maths ?!

[Mikkel]

And is mass in g or kg

Mate, as long as you're consistent you can use pounds for all I care...

If you want the velocity in cable lengths per forthnight - just make sure you convert the gravitational constant to cable lengths per fortnight squared and that the length of the wire is measured in cable lengths.

The SI unit for mass is kg - 1 g is equal to 1*10^-3 kg.

[moT]

Mate, as long as you're consistent you can use pounds for all I care...

If you want the velocity in cable lengths per forthnight - just make sure you convert the gravitational constant to cable lengths per fortnight squared and that the length of the wire is measured in cable lengths.

The SI unit for mass is kg - 1 g is equal to 1*10^-3 kg.

you sort of lost me there and is the gravitational consistant 9.8mps(squared)

[Mikkel]

you sort of lost me there and is the gravitational consistant 9.8mps(squared)

The gravitational constant is ~9.8 m/s^2 yes - varies slightly with your position on the planet... But it's in the range of 9.78-9.82 m/s^2. I think it's 9.81 m/s^2 here - but do the maths and you'll see it won't make much difference.

[moT]

The gravitational constant is ~9.8 m/s^2 yes - varies slightly with your position on the planet... But it's in the range of 9.78-9.82 m/s^2. I think it's 9.81 m/s^2 here - but do the maths and you'll see it won't make much difference.

and by consistancy you mean like everything is done in grams and centimeteres

[Mikkel]

and by consistancy you mean like everything is done in grams and centimeteres

I'd use kilograms and meters - however, as long as you use the same units throughout the equation you'll be fine whether you use grams and centimeters or pounds and inches.

[moT]

I'd use kilograms and meters - however, as long as you use the same units throughout the equation you'll be fine whether you use grams and centimeters or pounds and inches.

cheers you have been a great help im gonna try to get that test going asap

[Mikkel]

cheers you have been a great help im gonna try to get that test going asap

Make sure to take photos and keep us posted.

An idea for the pendulum would be to attach a bucket at a slight angle that'll gather the entire avocado. Just make sure it's light compared to the pendulum.

[BMW_RACER]

This isnt going to work very well.

[moT]

Make sure to take photos and keep us posted.

An idea for the pendulum would be to attach a bucket at a slight angle that'll gather the entire avocado. Just make sure it's light compared to the pendulum.

yer thats what i was thinking the avo normaly disintergrates on impact

[BMW_RACER]

I think the bucket might also disintigrate for some weird reason aswell.

[pritch]

Some people like a challenge and do things the hard way?

I have a chronograph for jobs such as this. Accurate answers, no pain, no strain. Basic models come cheap enough these days, and you get a special reduced price on a new one if you aim a bit low... :whistle:

[moT]

I think the bucket might also disintigrate for some weird reason aswell.

err well i wouldnt use a plastic bucket i might hammer together a box out of wood and shoot the avo into the box

[moT]

Some people like a challenge and do things the hard way?

I have a chronograph for jobs such as this. Accurate answers, no pain, no strain. Basic models come cheap enough these days, and you get a special reduced price on a new one if you aim a bit low... :whistle:

cornograph?

[BMW_RACER]

cornograph?

Chronograph.

Has two sensors, fire something between the two sensors and it tells you the FPS.

They are pretty cheap, Tim has one but I bet he wont let you fire your cannon at it.

[Swoop]

A chronograph is much easier!


Am I the first the raise the requirement for a firearms license...?
Not powered by a propellant powder... *enter Homer Simpson "WOOHOO!" here*

[Dave-]

how do you measure theta though mike?

by the time he gets the compass to the block of wood it would've settled.

nail in the end of the block with a paper sheet stretched out behind the pendulum? would take a few goes to find the approximate area the nail will pierce the sheet then its just simple geometry to work out your angle?

[ManDownUnder]

A chronograph is much easier!


Not powered by a propellant powder... *enter Homer Simpson "WOOHOO!" here*

Nor is an air rifle mate... and if you're under 18 you need one.

[Mikkel]

how do you measure theta though mike?

by the time he gets the compass to the block of wood it would've settled.

nail in the end of the block with a paper sheet stretched out behind the pendulum? would take a few goes to find the approximate area the nail will pierce the sheet then its just simple geometry to work out your angle?

I didn't say it was easy... But it is doable - without all the electronic bits and bobs.

If you have a video camera filming the pendulum from the side during impact would be the go. Choosing the weight of the pendulum so that you get just the right amount of deflection is critical though - too little deflection and you can not measure it, too much and it starts getting tricky again.

[kiwifruit]

Have you got lots of avos? Can i buy some?

[moT]

Have you got lots of avos? Can i buy some?

yeah tons too much to eat so im useing them as ammo

[doc]

Nope - the parabola calculation should provide you with the starting velocity, not the average. You don't directly measure the time it takes before the projectile touches down again - measure how far horizontally the projectile travels inside the timespan it takes for the projectile to reach the apex and return to the ground.
However you expect the ballistic profile to be a perfect parabola and it is not, due to wind resistance. Actually BMW_RACER has the essence of the parabola experiement sorted in the below quote - but that approach is not viable when using explosive shells or if you lack a precise stopwatch.

The reason I did not suggest the timing approach to measuring the muzzle velocity was quite simply that it is much more technical to do precisely. You need an electronic data logger and two sensors to respectively start and stop the logger.

Having a two point pivot on the pendulum using two wires could be sorted out in a way that would prevent spinning. The avocado will always deform, unless it's a crappy cannon - and there will be an energy loss there. It is imperative that all the avocado fragments are collected and swings with the pendulum, then the impact characteristics (bouncy or squashy) shouldn't matter.

If you have access to the right gear measuring muzzle velocity is both simple and precise.


you sort of lost me there .(squared)
Dumbass. :grouphug: :brick: I think I can speak for the rest of KB, it looks pretty simple to us.

[moT]

Dumbass. :grouphug: :brick: I think I can speak for the rest of KB, it looks pretty simple to us.

lol your funny

[lb99]

Pretty simple things. This one is Lynx powered.

Best barrel to chamber volume is 1:1.5

mine is just like that, I use the missus hairspray, the dearer the better.

mine is a perfect fit for a tennis ball, I havn't been able to get it to launch a surf line yet though :(

[The Pastor]

You need to time how long it takes to hit the ground and divide by distance to get an average velocity.

[mark247]

Have you got lots of avos? Can i buy some?


yeah tons too much to eat so im useing them as ammo

He was originally using the neighbours kiwifruit crop, until he found out. haha. This is one cool cannon. It fires for fucking miles.

[scumdog]

A chronograph is much easier!


Not powered by a propellant powder... *enter Homer Simpson "WOOHOO!" here*

It's a FIREarm - the missile is launched as a result of an explosion.

[nodrog]

He was originally using the neighbours kiwifruit crop, until he found out. haha. This is one cool cannon. It fires for fucking miles.

onions are the best, as they are close to round from standard, and you can peel them by layer to find the pefect fit.

[Colapop]

mine is just like that, I use the missus hairspray, the dearer the better.

mine is a perfect fit for a tennis ball, I havn't been able to get it to launch a surf line yet though :(
What is the best way to launch a surf line (in this manner)? I've heard of it being done but not sure how the mechanics would work. Yeah, ok, you could just stick your trace down the barrel after your projectile but will that carry it far enough or just drop it out the end of the barrel?

[Timmay]

There are three easy ways to do this:

1. Fire the avo straight up, measure the ammount of time it takes to return to ground. the fall is governed by acceleration due to gravity = 9.81m/s^2, The rise will be near enough linear deceleration causes by gravity, this almost totally eliminates air resistance due to going straight up the gravity factor massively outweighs the air resistance.

2. Hire the avo horizontally a set distance off the ground, measure the distance it takes before it hits the ground, the vertical fall of the avocado is governed by gravity = 9.81m/s^2 while the horizontal distance is governed by how fast the avo is going, it will hit the ground so soon air resistance will not be a factor.

3. make a striped velocity board, it will look like this

||||||||||||||||||||||||||||||||||||||||||||||||||

if you fire the avo past this board, and you know the spacing of the stripes and the frame rate of the camera you are using you can count how many stripes are passed per frame giving you the velocity.

I vote for the third method as easiest and most accurate.

PS, you could always find a willing cop with a speed camera to shoot at...

Looks like my engineering degree is useful for something after all

[jrandom]

Looks like my engineering degree is useful for something after all

I thought you just used it to pick up chicks.

[Mikkel]

1. Fire the avo straight up, measure the ammount of time it takes to return to ground. the fall is governed by acceleration due to gravity = 9.81m/s^2, The rise will be near enough linear deceleration causes by gravity, this almost totally eliminates air resistance due to going straight up the gravity factor massively outweighs the air resistance.

No. The wind resistance is proportional to the square of the velocity. You can not get around it without performing you experiment in a vacuum.

Although you are correct that the impact of wind resistance in this case will be less than for the parabolic experiment - simply because the projectile will not travel as far.


2. Hire the avo horizontally a set distance off the ground, measure the distance it takes before it hits the ground, the vertical fall of the avocado is governed by gravity = 9.81m/s^2 while the horizontal distance is governed by how fast the avo is going, it will hit the ground so soon air resistance will not be a factor.

...and the earth is flat.



3. make a striped velocity board, it will look like this

||||||||||||||||||||||||||||||||||||||||||||||||||

if you fire the avo past this board, and you know the spacing of the stripes and the frame rate of the camera you are using you can count how many stripes are passed per frame giving you the velocity.

This would work - however, let's say the exit velocity is 100 km/h this is equal to 27.78 m/s. Even if you had a camera that would be able to do a 10 fps capture you would need to measure a distance of ~2.8 m. Most consumer digital cameras can not achieve such fps. Besides, it's not unlikely that the avocado could be much faster than 100 km/h.

And we haven't even started thinking about aligning everything up, operating the camera and the cannon at the same time, getting the camera sitting at the right distance from the board to be able to get a decent field of view while still being able to resolve detail, etc...

The idea is good - but not that easy to implement.


I vote for the third method as easiest and most accurate.

PS, you could always find a willing cop with a speed camera to shoot at...

Looks like my engineering degree is useful for something after all

I'd have an immense respect for the cop who would be able to pick up the speed of a flying avocado with standard police equipment.


I thought you just used it to pick up chicks.

Nah mate, if you want to pick up chicks I guess poultry farming is the way to go.

[jrandom]

I'd have an immense respect for the cop who would be able to pick up the speed of a flying avocado with standard police equipment.

"scumdog, scumdog, he's our man..."

[vindy500]

to the post 3 up, if it was fired straight up wouldnt you need to know how high it went....

[Mikkel]

to the post 3 up, if it was fired straight up wouldnt you need to know how high it went....

If you knew how high it went you wouldn't need to record the time and vice versa.

[BMW_RACER]

Get a altimeter from a model rocket place, stick it in/on avocado. Find maximum height, apply maths etc.

[mark247]

Get a altimeter from a model rocket place, stick it in/on avocado. Find maximum height, apply maths etc.

you actually have good ideas?

[Dave-]

Get a altimeter from a model rocket place, stick it in/on avocado. Find maximum height, apply maths etc.

that'll only work if you attach altimeters to all your avocados...it'll also only work if you're high enough to witness and record the highest altitude, unfortunately for you glue does not always work but it seems to keep your posts consistent.



This would work - however, let's say the exit velocity is 100 km/h this is equal to 27.78 m/s. Even if you had a camera that would be able to do a 10 fps capture you would need to measure a distance of ~2.8 m. Most consumer digital cameras can not achieve such fps. Besides, it's not unlikely that the avocado could be much faster than 100 km/h.


high def video camera :P

only $1800...

[Patar]

yer thats what i was thinking the avo normaly disintergrates on impact

Mate, if you want the velocity of the avocado the best thing you can do is find a wall, measure 10m from the wall to the end of the nozzle, shoot and measure the time it takes to hit the wall, do a couple of these, average it out and you will have a fairly good average velocity.

i.e
Distance= 10m
Time taken to hit wall = 1.7s
Velocity = 10/1.7 = 5.9 m/s x 3.6 = 21.2 km/h

This is a) an infinite amount of times easier, b) most likely a lot more accurate as statistically speaking human error should be normally distributed having a mean error of zero, and wind resistance is negligible.
Not to mention all the difficulties in measuring angle of deflection on impact, actually hitting the block, assuming no friction loss in the roatation of the block.

If you really want an accurate measure of velocity, set up a video camera and a scale beside the muzzle and play back the clip measuring the distance the avocado moves per frame.

[Mikkel]

You got a filthy mouth on you BMW_RACER - any progress with the DEI kit yet?


that'll only work if you attach altimeters to all your avocados...it'll also only work if you're high enough to witness and record the highest altitude, unfortunately for you glue does not always work but it seems to keep your posts consistent.

The altimeter idea doesn't work for the simple reason that they are not very precise. Even with state-of-the-art GPS gear it'll take a couple of seconds to get the height just fairly precise.

A common altimeter which works based on air pressure is far less accurate and sensitive.


high def video camera :P

only $1800...

HD doesn't matter. What is important is the FPS - and how consistent this is.


delete me.

You can do that yourself - you should be a senior member by now. (Think edit...)


Mate, if you want the velocity of the avocado the best thing you can do is find a wall, measure 10m from the wall to the end of the nozzle, shoot and measure the time it takes to hit the wall, do a couple of these, average it out and you will have a fairly good average velocity.

i.e
Distance= 10m
Time taken to hit wall = 1.7s
Velocity = 10/1.7 = 5.9 m/s x 3.6 = 21.2 km/h

This is a) an infinite amount of times easier, b) most likely a lot more accurate as statistically speaking human error should be normally distributed having a mean error of zero, and wind resistance is negligible.
Not to mention all the difficulties in measuring angle of deflection on impact, actually hitting the block, assuming no friction loss in the roatation of the block.

If you really want an accurate measure of velocity, set up a video camera and a scale beside the muzzle and play back the clip measuring the distance the avocado moves per frame.

Good idea - except that the speed is likely to be considerably higher than 21.2 km/h and therefore it becomes very tricky to measure the time precisely with a handheld stopwatch -> specialist equipment -> dollars.

Then you may say that we'll just use a distance of 50 meters - however then we get into trouble with the trajectory and the fact that you are measuring the average speed over said distance.

[BMW_RACER]

Who cares, just shoot shit with it.

[scumdog]

Who cares, just shoot shit with it.

Who frikin cares about how bloody fast an avocado will goo...sheesh, get a life!:bash:

[jrandom]

Who frikin cares about how bloody fast an avocado will goo...

Faster than the Eagle auw!

:eek:

[Patar]

You got a filthy mouth on you BMW_RACER - any progress with the DEI kit yet?



The altimeter idea doesn't work for the simple reason that they are not very precise. Even with state-of-the-art GPS gear it'll take a couple of seconds to get the height just fairly precise.

A common altimeter which works based on air pressure is far less accurate and sensitive.



HD doesn't matter. What is important is the FPS - and how consistent this is.



You can do that yourself - you should be a senior member by now. (Think edit...)



Good idea - except that the speed is likely to be considerably higher than 21.2 km/h and therefore it becomes very tricky to measure the time precisely with a handheld stopwatch -> specialist equipment -> dollars.

Then you may say that we'll just use a distance of 50 meters - however then we get into trouble with the trajectory and the fact that you are measuring the average speed over said distance.

maybe i'm just an idiot but why on earth would he need it very precise?
also if it's done over a distance of say 20-30m all it would take to get a good average reading would be 10 shots with 2-3 people recording the time taken. This should give a fairly sufficient estimate at what the velocity is, especially considering the variability in mass of avocado and air/fuel mixture

[moT]

Who frikin cares about how bloody fast an avocado will goo...sheesh, get a life!:bash:

Me i have an interest in trajectorys and maths i like to know how stuff works

[BMW_RACER]

Who frikin cares about how bloody fast an avocado will goo...sheesh, get a life!:bash:

Was that directed at me? If so I think you misinterpreted my post :Pokey:

[Mikkel]

maybe i'm just an idiot but why on earth would he need it very precise?

If you're going to do a job - at least do it well.

Either do or don't - the half-arsed approach is a waste of time.

Now, this is more of an exercise in how to do the measurement without all sorts of fancy specialist equipment - and still get a fairly accurate measurement.

[Ocean1]

Point the fucker straight up.
Measure off 100M horizontally.
Get a sextant... OK so it’s moderately specialised… use a protractor and a sighting tube.
Fire said fucker.
Pick the max altitude with the protractor/sight.
Make with the trigstuff.


Clamp the fucker to a skateboard along with enough weight to make up, say, 10kg.
Weigh the avo.
Fire fucker.
Measure recoil distance.
Make with the numbers.

[vindy500]

i remember our science center used to have a cricket net where you bowled the ball and it told you how fast it was.... that could work

[Shadows]

Or you could just use a chronograph.

Wot he said. Somebody (or maybe a gun shop if you ask nicely enough and maybe flick 'em some cash) must have one you can borrow. FFS don't tell them what you are measuring though. Tell 'em you're reloading cartridges for a .303 or something.

And by the way you need a firearms license to possess or use a spud gun.

[Dave-]

HD doesn't matter. What is important is the FPS - and how consistent this is.


some new digi video cameras are coming out with 1080p60 which is 60fps 1080 video.

the reason i say 1080 is important is so you can see the lines clearly from a fair distance away which as you state you may have to do to fit in a decent sized ruler.

id cap my video using marks on a wall or a few cones or something, drop the video into after effects or premiere, throw some guide lines in and count the number of notches the avocado moves in 60 frames and say its moving at xm/s

you'd probably even get away with 25fps

the frame rate will be dead accurate and consistent unless you shoot on NTSC then your maths will have lots of decimal places :)

[pritch]

mine is a perfect fit for a tennis ball, I havn't been able to get it to launch a surf line yet though :(

I met a guy who had done some work on that.

He was at the stage where he had discovered that a length of Bungee cord as a shock leader was necessary. He was making "bullets" on a wood lathe but until he hit on the bungee idea he had launched a succession of projectiles waaay out to sea. He was attaining very impressive distances but still had his fishing tackle at his feet.

The line would be dealt with similarly to the system you would use with a fishing kite, a spool on the ground beside the gun so that the line could just peel off. No reel is going to spin fast enough.

The "bullets" worked really well but a big chunk of bait and a sinker being dragged behind it through the air would lower the ballistic coefficient dramatically.

As a friendly Police Inspector said though this should be done well away from crowds...

[Rollestonchick]

Omg Tom are you bored this weekend? Pmsl.

[BMW_RACER]

some new digi video cameras are coming out with 1080p60 which is 60fps 1080 video.

the reason i say 1080 is important is so you can see the lines clearly from a fair distance away which as you state you may have to do to fit in a decent sized ruler.

id cap my video using marks on a wall or a few cones or something, drop the video into after effects or premiere, throw some guide lines in and count the number of notches the avocado moves in 60 frames and say its moving at xm/s

you'd probably even get away with 25fps

the frame rate will be dead accurate and consistent unless you shoot on NTSC then your maths will have lots of decimal places :)

Yeah im sure hes got like 5k or so to drop on a hi def camera and premiere / aftereffects just to try and find out the FPS of his cannon.

[westie]

there has to be someone here better at maths than i am

You lost me at maths:wacko:

[Nagash]

Err.. not gonna bother reading through 7 pages but working out the velocity should be bloody easy..

V=dt (Velocity = Distance / time)

So really, get a mate with a stop watch, fire the avocado, time from when you launched it to when it lands. Measure the distance, and divide the 2 digits together. Viola, you have it's velocity in metres per second.. Granted it's only the average velocity but you only wanted a rough estimate..


[Edit] Okay, this has been pretty much suggested on every single page... I fail to see where the problem is.

[moT]

[Edit] Okay, this has been pretty much suggested on every single page... I fail to see where the problem is.

there is lots of error involved and gives a false reading shooting the block and working it out that way is a more precice measurement of mussle velocity