The LEGO Catapult

Everyone takes breaks at work. Some people take smoke breaks. Others go on a walk around the building. Me? I play with LEGOs. I figure if people can take a 10-minute smoke break every couple hours, I can certainly take a 10-minute LEGO break. And what happens when you give three engineers a bucket of LEGO bricks and a couple days of 10-minute LEGO breaks? You get the LEGO Catapult.

This is a functioning catapult built entirely out of LEGO bricks. The only “foreign” objects included in the build are rubberbands, which gives the catapult its power. The catapult shown is actually the second catapult we built. The first catapult kind of just happened as we casually played with the bricks. Once of said, “We got any rubberbands,” and a prototype catapult up and working.

While our first model was great and it worked, it lacked a few things. First was power. The prototype had a good arc shot but it used several standard-sized rubberbands wrapped in an odd fashion that lent to breaking bands and flying bricks. The trigger mechanism was also extremely weak. After every shot we had to carefully put the trigger back in place to keep the launch arm down while we loaded up our projectile.

The current model we really thought about what would make a good design that would be stable and provide for maximum power. The catapult was built with your generic LEGO bricks for the housing and limited use of Technics LEGO bricks to achieve rotation bricks and axles.

The “engine” uses two .25-inch rubberbands. The launch arm has two tire hubs at the end that the rubberbands go around. Another hub is lower and near the back of the housing, the bands go over this hub and then around a third hub that is near the bottom of the housing and right below the hubs on the arm. The second hub is adjustable, so if we want more or less power we can move it, but during testing we found the distance between brick holes made the stretch too much - in that it would pull the bricks right off the housing - or not enough power.

The new trigger mechanism is a LEGO door frame (from the old LEGO sets) attached to hinged bricks. One bricked tire axle is used keep the trigger rubberband from rubbing against the hard edge of a normal block. That rubberband is stretched just barely around a stack of bricks so that when the trigger is pulled back to release the arm, it is immediately pulled back into place ready to be cocked again. On top of the trigger is a roof brick that lines up with a hull brick under the end of the arm. This way when you push the arm down the two pieces slide against each other and the end of the arm is held by the top of the door frame.

The arm itself had one major problem - the brick nubs! The nubs would catch on various objects we launched, so we needed a smooth launch pad. We dug out all the novelty plates and put them on the end of the arm (hence all the arrows in the pictures). This allows any projectile to slide off as it is launched giving it a nice arc.

Our standard for shot testing was a regulation LEGO man with a helmet. Afterall, when you’re riding a catapult you gotta think safety first. However, a LEGO guy equipped with a helmet and backpack made a much better weight that gave the man more arc and distance.

The trick to a good shot is the weight of the object and its position on the launch arm. Putting the object near the bottom of the launch arm made for a straighter shot while putting it at the end of the arm gave it more arc and height.

The catapult is built on the dividing wall that separates my workspace from that of my co-workers. The wall is roughly 4-inches wide and the catapult itself is a about a foot long, give or take. The catapult is pointed towards the wall in order office that has our whiteboard on it. So to give us a little more motivation for the project, we taped styrofoam cups to the wall as targets.

The catapult is pretty hefty and can launch a variety of objects. Beyond your LEGO men, we regularly launch MUSCLE Men, Hot Wheels cars, and plastic army men. We once launched a peanut and the peanut actually cracked when it hit the wall. We also took an old mouse and took out the ball and shaved off the rubber coating. At the heart of a mouse ball is a solid metal ball, we guess steel or something. It’s pretty heavy but the catapult can handle it, although it doesn’t launch it nearly as far.

All in all, we’re quite proud of the LEGO Catapult and now the activity of catapulting fills in our 10-minute play breaks. We’re not sure how long we’ll keep the catapult around. It’s serving us quite well right now, but we’ll certainly think up something else to build…and hopefully it can shoot something too!

Personally, I was amazed what four rubberbands can do for some LEGOs. If only I had thought about it when I was little. Man, I could have built a ton of stuff that actually had some functionality.