Noob possum got pwned by avo cannon

[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. I think I can speak for the rest of KB, it looks pretty simple to us.

[moT]

Dumbass. 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:Me]

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.