I need to build a catapult -- HELP!!

[jodog]

The grandkid needs a catapult for a school project that shoots a marshmallow at least 10 feet. Well I can do that, but the teacher told me something I didn't need to hear. The record is 77 feet.

I have built dead-weight trebuchets, bungie powered catapults, and spring powered catapults. I have googled. The best distance I have gotten is around 50 ft.

So far, spring power is the best but the power of the spring has destroyed 2 axles and one stop bar. This may be the catapult equivalent of a Corvair -- unsafe at any speed.

Oh, it has to be carried by an 11 year old on a bus to a class room and then to a football field. Size matters, and of course you can't disturb the sacred football field.

Any ideas?

Bob

 

[DannoXYZ]

potato gun powered by ether
Are you allowed to aerodynamically shape marshmallow before launching?

 

[ibike2havefun]

Trebuchet in front of a very large fan?

 

[DannoXYZ]

Trebuchet in front of a very large fan?

jet engine!!!

 

[STFlips]

Soak the marshmallow in water and then freeze it.

 

[Nashcat]

Are we talking, full-size or mini marshmallows? Stale or fresh? I would think that old, stale marshmallows would travel further. Are slingshots allowed?

 

[rogo]

I've launched marshmallows with an air cannon.
They become denser after launch.
Good for a 100 yds maybe.
A catapulted marshmallow off a fishing pole? Bungee cords should pack enough power.

 

[SMSW]

I'd salvage a garage door's torsion spring. You will have to find a way to preload it by twisting the end not attached to the throwing arm. I'd use a short section of the pipe (or say 3/4' electrical conduit (EMT)) for an axle. In fact, I plan to use these materials hopefully this summer to build a squirrel launcher....

There was a TV show - Northern Lights(???) - and in one of the episodes a grand piano was launched from a very large trebuchet. The piano did not survive its landing.

 

[Larry Fine]

There was a TV show - Northern Lights(???) - and in one of the episodes a grand piano was launched from a very large trebuchet. The piano did not survive its landing.

That was key.

 

[SMSW]

Another propulsive device occurred to me. You can buy air tanks for paintball guns that can be filled with compressed air up to 3000 or 4500 psi (different groups of tanks). By modifying a cheap paintball gun and using an air cylinder, you should be able to flip the throwing arm of a catapult at very high speeds. Paintballs are limited to around 280fps but you can probably get better than that at the end of the lever arm for your catapult.

I also like the idea of increasing the density of the projectile - not by cheating like those anglers who were dropping lead weights down the gullets of fish caught in fishing tournaments here in Ohio. (As I remember, they were fined tens of thousands of $$$ and got jail sentences.) You will have to explore ways of reducing the size of said marshmellows -drying???- and then infusing them with water and freezing them.

 

[jodog]

Creative ideas all. The marshmellows are provided and cannot be altered in any way. Air Cannons and some of the other ideas seem like a lot to ask an 11 year old to handle, or even carry, to the test site. Garage door tension springs? Come on guys, put on your thinking caps. Whole thing needs to weigh 15 lbs or so, be easy to set up and operate, and be SAFE.

I just feel bad about not being able to obliterate the record.

The general wisdom is the short end of the swing arm to long end ration should be about 1:4. Dead weight trebuchet won't work as the weight is too much. Bungies don't provide enough distance, and surgical tubing has to be stretched A LOT. Ideas! Better yet sketches!

 

[Igofar]

Insert a steel ball bearing inside the marsh mellow for weight

 

[Larry Fine]

 

[W0QNX]

Creative ideas all. The marshmellows are provided and cannot be altered in any way. Air Cannons and some of the other ideas seem like a lot to ask an 11 year old to handle, or even carry, to the test site. Garage door tension springs? Come on guys, put on your thinking caps. Whole thing needs to weigh 15 lbs or so, be easy to set up and operate, and be SAFE.

I just feel bad about not being able to obliterate the record.

The general wisdom is the short end of the swing arm to long end ration should be about 1:4. Dead weight trebuchet won't work as the weight is too much. Bungies don't provide enough distance, and surgical tubing has to be stretched A LOT. Ideas! Better yet sketches!

So use rubber bands. Bands around the long lever wrapped down over the axle to a hook at the base of the uprights.

 

[ibike2havefun]

There was a TV show - Northern Lights(???) - and in one of the episodes a grand piano was launched from a very large trebuchet. The piano did not survive its landing.

Close- Northern Exposure.

 

[SMSW]

Insert a steel ball bearing inside the marsh mellow for weight

They use tungsten in Soapbox Derby cars. It is more dense than steel or lead. Depleted uranium is just too hard to get...unless you live near an old battlefield.

 

[Nashcat]

Whole thing needs to weigh 15 lbs or so

Well, that ruins my plans. I was thinking automotive leaf spring, with a come-a-long to cock it. Then, light the marshmallow afire and storm the castle.

John

 

[Sadlsor]

This whole escapade smacks of mechanical engineering.
I can operate a firearm (not for this instance, I'm sure), or many ancient or modern devices which are designed by those smarter than myself. (Which is a wide and deep pool of talent, to be sure.)
But I will enjoy watching the brilliance here, like I enjoy watching fireflies on a summer's eve (soon), or fireworks in the night sky.

 

[Cogmeister]

Streamline the marsh mallow

 

[northwestparider]

I helped my eldest build one a couple of years ago. We did the basic bungee cord one. One thing I noticed that impacts distance is release point. Where is the "basket" in the arc of travel when it stops. It needs to be before being perpendicular to the ground.

We used a board as the launch arm. Afterwards I thought of a two piece arm. Solid on the bottom and flexible on the basket end. This would be to gain some who action like a golf club arcs when swung. This may make figuring out the stop point for the solid part of the arm trickier so that the "basket" doesn't exceed perpendicular to the ground.