Most accurate mid-range projectile launcher

[Peter F]

< Mentor Note -- thread moved to HH from the technical physics forums, so no HH Template is shown >

Hello everyone,

I am a mechanical engineering student and was given the task to design a very accurate projectile launcher within a distance of 10 to 20 meters. It should be adjustable within that range and portable by one person. Accuracy is the most important though. I was thinking of a crossbow operated with a spring or a skeet shooter would fit the description well. Any ideas would be highly appreciated. Thank you in advance

 

[Evanish]

Hello everyone,

I am a mechanical engineering student and was given the task to design a very accurate projectile launcher within a distance of 10 to 20 meters. It should be adjustable within that range and portable by one person. Accuracy is the most important though. I was thinking of a crossbow operated with a spring or a skeet shooter would fit the description well. Any ideas would be highly appreciated. Thank you in advance

What about natural gas as a propellant? You could make a mini artillery piece. Maybe you could use some parts from a car like spark-plug, fuel injector etc.

 

[anorlunda]

Presumably, firearms are not allowed. What are the complete and accurate requirements that you're working with?

 

[berkeman]

Welcome to the PF, @Peter F

Since this project is for your schoolwork, I've moved your thread to the schoolwork forums.

As @anorlunda asks -- please post the exact wording of the project requirements. So far there are too many variables to help you much.

Also, please say more about your ideas so far. If accuracy is very important, what design factors go into a very accurate launcher and an accurate projectile?

 

[CWatters]

Peter - What factors do you think affect the range?

 

[Peter F]

Thank you everyone for your prompt responses. Thank you @berkeman for moving it into the appropriate topic, I was not aware.

The main factor affecting range will be the launch velocity and the launch angle. The release of trigger mechanism needs to be operated from at least 1.5m. The maximum operating force is 50N (which could be used to create a larger force through transmission) and the projectile is a 120g bean bag.

The resources available are steel and aluminium tubes, sheets, plates and round bars. Chains, bearings, belt drives and gears could be selected from standard catalogues. Principal design tasks are energy storage method, a mechanical ‘transmission’, launching mechanism and overall design.

The main aim of the task is to be able to adjust the range of the launcher based on a mathematical model between 10 and 20m reliably and most importantly very accurately. We thought about multiple methods such as trebuchet or mangonel but arrived at skeet shooters and a spring operated crossbow due to their high accuracy, adjustability and convenient trigger mechanism.

If there are any other opinions about this, they would be highly appreciated though. Thank you!

 

[CWatters]

So once the correct launch velocity an angle have been found the next thing will be ensuring those and the results are repeatable. You might want to consider what factors might effect the flight path of a bean bag and is there anything you can do to make it more repeatable.

 

[berkeman]

As @anorlunda asks -- please post the exact wording of the project requirements.

FYI, your more detailed description above helps, but it really would help us to see the exact wording of the assignment. Otherwise, we have to ask too many follow-up questions, like this one:

the projectile is a 120g bean bag

What is the beanbag put in for the launch? Are you given a standard cup of some sort, or just given the beanbag? If the latter, can you stuff the beanbag in a more aerodynamic container with directional stabilizers (like a little rocket ship shape)? Or is is supposed to just be a beanbag blob from start to finish?

(See what I mean?)

Okay, other questions/ thoughts:

The main factor affecting range will be the launch velocity and the launch angle.

Those are the gross factors, what are the fine factors that will determine the winner? There are a couple...

The main aim of the task is to be able to adjust the range of the launcher based on a mathematical model between 10 and 20m reliably and most importantly very accurately

What do you mean by "a mathematical model"? You are not allowed to fine-tune your settings and calibration constants with experiments?

arrived at skeet shooters and a spring operated crossbow

In my practical experience, skeet pigeon launch arms are notoriously variable. Are you sure about trying to use that paradigm? And a crossbow design would probably only be accurate if you can use the stuff-the-beanbag-in-the-model-rocket trick I mentioned above...

Fun project overall, but please give more info, and think more about what-all is involved in great accuracy in projectile motion. BTW, will you be filing a report of your group's work too, or is the full grade just based on the accuracy performance in the final testing?

https://s7d2.scene7.com/is/image/dkscdn/16DTRUBCKYRD34CLYTGS_is/

 

[diogenesNY]

Is trajectory an important part of the assignment? or do you just have to land the beanbag on a target, regardless of the space it passes through?

diogenesNY

 

[Peter F]

Thanks again for the quick replies!

What is the beanbag put in for the launch? Are you given a standard cup of some sort, or just given the beanbag? If the latter, can you stuff the beanbag in a more aerodynamic container with directional stabilizers (like a little rocket ship shape)? Or is is supposed to just be a beanbag blob from start to finish?

We are free to choose where to put the beanbag. However, we cannot edit the ball. The focus is on the launcher itself.

What do you mean by "a mathematical model"? You are not allowed to fine-tune your settings and calibration constants with experiments?

We can experiment, however we are given the aim (which will be between 10m and 20m) on the day and need to adjust accordingly. Therefore, we need to come up with a model that allows us to adjust the angle and tension so the projectile is as close to the aim as possible. We cannot test it on the day.

Fun project overall, but please give more info, and think more about what-all is involved in great accuracy in projectile motion. BTW, will you be filing a report of your group's work too, or is the full grade just based on the accuracy performance in the final testing?

We will have a report too. The main point of the project is to design a launcher whose angle and launch velocity can be adjusted using a model in order to accurately land it reliably on a target in a range between 10m and 20m.

Is trajectory an important part of the assignment? or do you just have to land the beanbag on a target, regardless of the space it passes through?

Not important, just need to land the beanbag.

I hope that makes sense. Thank you!

 

[diogenesNY]

For the description you have given, I suspect that a simple trebuchet

https://en.wikipedia.org/wiki/Trebuchet

would be an excellent solution:

It meets your specifications.
The design is time tested and well understood.
The physics and engineering are also well understood and easily demonstrable and all principles are citable in abundance.
Relatively few moving parts, and relatively few variables to consider, and all those variables are pretty easily documentable and demonstrable and can be pretty well calculated (or experimentally adjusted).
Comparatively simple to construct.
The main user experimental variable will simply be adding weight to the 'bob'.
Doesn't require springs or materials under complex tension for propulsion.

I am following a guiding principle that simpler is better.
Should be relatively easy, with a few weigh adjustments to put your beanbag right on its target.

Anyway, just a thought. I figure it would also be fun (and fairly easy) to build, and lots of fun to play with after the project is over. :)

diogenesNY

 

[Peter F]

For the description you have given, I suspect that a simple trebuchet

https://en.wikipedia.org/wiki/Trebuchet

would be an excellent solution:

It meets your specifications.
The design is time tested and well understood.
The physics and engineering are also well understood and easily demonstrable and all principles are citable in abundance.
Relatively few moving parts, and relatively few variables to consider, and all those variables are pretty easily documentable and demonstrable and can be pretty well calculated (or experimentally adjusted).
Comparatively simple to construct.
The main user experimental variable will simply be adding weight to the 'bob'.
Doesn't require springs or materials under complex tension for propulsion.

I am following a guiding principle that simpler is better.
Should be relatively easy, with a few weigh adjustments to put your beanbag right on its target.

Anyway, just a thought. I figure it would also be fun (and fairly easy) to build, and lots of fun to play with after the project is over. :)

diogenesNY

Thank you for the reply, that was very helpful. Due to portability issues, we decided against the trebuchet. Thank you again for the answers!

 

[diogenesNY]

Keep us posted!

I would be interested to know what you eventually decide on, and how it works out. Sounds like a neat project.

diogenesNY