Over complicating a project (ideas)

[VoidsWarranties]

Our high school has a competition for someone or a team to design a catapult that will shoot soft baseballs not softballs like rubber baseballs.
Rules/goals:
Arm no longer than 4ft
Body volume 3x3x2ft
Distances 140ft and between 120 and 240ft
(Second distance will be given at the competition)
No weight or material limits
Must be a catapult not a trebuchet

Now for the over complicated part(after we get the main body working of course).  One of my friends happens to be a good programmer and I happen to be good at the hardware side so he said he wanted it to be able to calculate the power of the arm and pull or tell us where to pull the arm back to.  We have plenty of options to move the arm, steppers, wheelchair motors, etc.  I am just looking for any suggestions on what to do to get it as overly complicated as possible(obviously we can do it simpler but then the coolness factor decreases)


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[Mr. Scram]

When is the size of the thing established? Might it be possible to do some kind of fold out mechanism? It might be worth it to look at the rules very closely and carefully and see what section leaves enough ambiguity to build that one thing that is technically correct, but obviously not what was intended

[VoidsWarranties]

These are the very vague rules:



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[Mr. Scram]

Unfortunately, the arm length and explicit catapult requirements limit things quite a bit. You might want to look for exotic catapult system, though. An exotic catapult is still that.

The one thing I do notice it that the dimensions do not state which dimension is what. You might be able to use that to your advantage.

[Mr. Scram]

Looking at the catapult disambiguation on Wikipedia, quite a lot is possible. Even if you adhere to the traditional meaning of catapult, quite a lot of different machines can be intended.

Traditional machines in various shapes and sizes: https://en.wikipedia.org/wiki/Catapult
Modern artillery: https://en.wikipedia.org/wiki/M-46_Catapult
Steam powered: https://en.wikipedia.org/wiki/Aircraft_catapult
Physics effect: https://en.wikipedia.org/wiki/Catapult_effect

[Ian.M]

I belive the most 'bang for your buck' given those dimension limitations will be a sling Onager, as the sling acts as an extension of the arm.
See http://www.sg.sca.org.nz/docs/OnagerManual.pdf

If you want to pimp it out with hi-tech gadgetry, consider adding accelerometers, and strain gauges or load cells to monitor the stored energy and the efficiency in transferring it to the projectile, a laser sight for aiming, a rangefinder and wireless data acquisition back to a gunnery computer.  Done right, with a well built mechanism you could have a high probability of a 'one shot kill'.

I wouldn't add any electric actuators - if anything goes wrong on the day you would be FUBARed, and its very difficult to come up with something more effective than a man with a 5' steel pipe capstan bar.   

[Mr. Scram]

I belive the most 'bang for your buck' given those dimension limitations will be a sling Onager, as the sling acts as an extension of the arm.

It is important to note that maximum range is not that important, but that accuracy at a set and an additional unknown range is.

[Phoenix]

How about a rail gun? It's not a far stretch from an aircraft launcher...

[VoidsWarranties]

How about a rail gun? It's not a far stretch from an aircraft launcher...

I wish, but i think it must be closer to a pivoting arm with some sort of elastic or stretchy material or item to swing the arm and fire the object


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[Mr. Scram]

I wish, but i think it must be closer to a pivoting arm with some sort of elastic or stretchy material or item to swing the arm and fire the object

The rules are what they are. The rules explicitly state that it must be a catapult design. Building something that uses the catapult effect seems to be easily within those requirements. Just like it is important to label your axes, it is also important to carefully define requirements. If the teaches don't teach the children, you might have to resort to the opposite.

[Mr. Scram]

Not sure if that still falls within the strictest definition of a catapult though.

Look at the various contraptions under the Wikipedia entry for the term catapult. It being a family of devices, or even a couple of families, should yield plenty of leeway to stray from the obvious solution. Whether a paddle can be made to fit, I don't know, but there is bound to be something in there.

Elegance is great if you want to build something useful. If you build an inherently useless contraption, overdoing it seems more fun 

[John at the Falls]

What will be impressive will not be the catapult itself but the targeting system you build to accurately hit your target. Solving the targeting problem can use the time and energy wasted trying to be cool.

Do not confuse cool and clown.
Something "cool looking" will only make you look like a clown if does not even come close to performing.

[Mr. Scram]

Something "cool looking" will only make you look like a clown if does not even come close to performing.

I'm not sure I agree. Shooting for the stars and failing miserably might be a lot better than to middle-of-the-road the thing and do decent.

[VoidsWarranties]

What will be impressive will not be the catapult itself but the targeting system you build to accurately hit your target. Solving the targeting problem can use the time and energy wasted trying to be cool.

Do not confuse cool and clown.
Something "cool looking" will only make you look like a clown if does not even come close to performing.

That is exactly what I want to figure out how to make, a targeting system.  Of course I will have to get the main mechanism done first.  You can just attach bits of electronics to it if you want it to look cool but I want the way it works to be cool(and accurate )


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[HAL-42b]

If I were you I'd look into spearfishing guns and try to use their supplies and materials. The rubber tubes they use are perfect for your application and you especially would not want to design your own trigger mechanism since it affects accuracy and reliability. Buy a ready made trigger assy for 30$ and you will be ahead of the game.

[Smokey]

It didn't say it had to be an elastic potential energy system.  Just get an industrial servo motor, an industrial servo drive amplifier, and hook it up to an arm with a basket at the end.  Assuming you can come up with some really stable way to mount it (bolted down to the concrete?) you can have very accurate motion control and with some calibration before hand you should be able to hit specific distances no problem.  You could even manually adjust lateral positioning, like axis aligned rifle scope sighted to target or something, then lock it down.

[Mr. Scram]

It didn't say it had to be an elastic potential energy system.  Just get an industrial servo motor, an industrial servo drive amplifier, and hook it up to an arm with a basket at the end.  Assuming you can come up with some really stable way to mount it (bolted down to the concrete?) you can have very accurate motion control and with some calibration before hand you should be able to hit specific distances no problem.  You could even manually adjust lateral positioning, like axis aligned rifle scope sighted to target or something, then lock it down.

If you can accurately control the motion of a launch system, ballistic calculations which also compensate for wind direction and elevation should be fairly trivial. The only real problem is that round balls tend to drift over longer distances.

The rules do not forbid giving your ball a more aerodynamic shape. That should greatly improve the accuracy.

[Smokey]

Hopefully they are talking about those dimpled pitching machine balls.


If the deal is that the balls are so un-aerodynamic that you can't predict their flight characteristics, then it doesn't matter what anyone does for a machine since it's completely random.  Everyone will be tossing and praying so you might as well just give up now.

[tpowell1830]

Ok, looks like you are dealing with a simple catapult. Work the targeting system as best you can, but put a lot of LEDs on it, for instance in the shape of an arrow and have the LEDs turn on in a cascading fashion where the rows in back light up first and move toward the point of the arrow.  Have the LED arrow be pointed generally at the target area. Add sounds and more LEDs at your discretion. Make it cool and interesting for all observers. 

[John at the Falls]

So how did the competition turn out?

[Luminax]

Hmmm... if I were to nitpick, catapult is the "name of the method employed by such weaponry" and trebuchet IS a catapult...
Looking at the few posts, I'm guessing you want a Ballista? Onager? Could it be classifications by propulsion?
I suggest you clarify this with the teacher/instructor/board

[SL4P]

Dave -
Can you restrict viewership of this thread ?   
We don't want North Korea to get any ideas.

[tszaboo]

We have plenty of options to move the arm, steppers, wheelchair motors, etc.  I am just looking for any suggestions on what to do to get it as overly complicated as possible(obviously we can do it simpler but then the coolness factor decreases)

Make sure it has a raspberry pi with a web server tied into amazon azure and the pi only needs relay. Then you can say:
"Alexa, rain hell" to shoot. That is as complicated as it gets.

[Ian.M]

You want to over-complicate it?  Use an electric wheelchair chassis, and build a mangonel on it with a motorised rearming mechanism, a tube feeder for the ball ammunition, and the aforementioned Raspberry Pi for voice command and control.  Think ED-209 meets SCA!

[Luminax]

I think we can all collectively agree that "Catapult, not trebuchet" thing this person have in his mind is a Mangonel/Siege Onager, yes?

... explosion powered mangonel anyone?