## Introduction: MAKE a SPRING-ACTION MORTAR WITH ADJUSTABLE HEIGHT (using a Plastic Beer Jar and Discarded Stuff)

A few months ago, I had to help a cousin of mine with a college homework about the physics of parabolic trajectory. He's really good at math, but very bad at crafting. It was my turn to save the day!!

I had only one night to build a machine capable of launching an anti-stress ball, with adjustable height. So, I combined a plastic beer jar (marketing stuff from a colombian beer named "Costeña"), a toilet tree for the elevation and other stuff for the frame. It works with two spings, like some type of slingshot. You charge the mortar, lock the trigger, push the trigger and it launch the ball.

LEARNING OBJECTIVE:

By building this Spring-Action Mortar, students will be able to build a educational project reusing stuff and analize the physics of launching a projectile with parabolic trajectory.

## Step 1: Materials and Stuff

You will need the following materials:

• Acrylic beer jar
• Sheet made of acrylic or another hard plastic.
• Electric shower case, that fits in the jar mouth.
• Two springs (for the "slingshot")
• One smaller spring (for the trigger)
• One PC screen base
• Two printer pieces (for the mortar mount)
• Toilet plastic floater graduating piece (tree)
• Hinge
• Metallic angles
• parfum round cap
• bolts and screws
• Two key chain rings
• round telephone cover
• vents (for fixing the mortar to the ground)
• vaseline
• anti stress balls
TOOLS:
• Dremel
• Screwdivers
• Pliers
• Tweezers

And remember:

1. If you don't have it, replace it!
2. Use protective equipment (dust mask and goggles)
3. Beware of drilled and soldered hot surfaces
4. Work in a good ventilated area.
5. Always have junk in stock
6. Enjoy!

## Step 2: The Barrel

Cut the shower case in the way showed on the picture. It will be the mortar muzzle, and later you will fix the springs to it.

Make two grooves, each one opposed to the other. They will be the rails of the launcher.

Fit the shower case to the jar, and glue or fix with screws.

## Step 3: The Slingshot

Insert the springs in each side of the jar, aligned with the grooves.

Take a hard plastic plate to make the launcher. It has to slide in the grooves. It will  have holes in each side for fasting the spings. In the middle, it will have a hole where the nail of the trigger will fit. The parfum's cap will be ahead the launcher, for a better shooting of the ball.

## Step 4: The Trigger (Part 1)

For the trigger, take an acrylic piece and work it removing the black marked area. You have to create a nail with a quoin so, when you pull back the launcher, it pushes down the trigger, and when the trigger elevates, it inserts the nail into the center hole of the launcher. The shoot will be produced when you press the trigger, releasing the launcher.

7.

Make two grooves in the base of the jar: One small on the upper side (where you can slide the upper part of the trigger), and one bigger on the bottom side (where you can slide the lower part of the trigger). Put some grease on the trigger and insert it.

8.

## Step 5: The Trigger (Part 2)

Put a spring in the upper part of the trigger so, when you push and release it, it will come back to the original position. Attach the plastic disc using the iron angle, making the spring get trapped between the disc and the jar.

9.   On the lower part of the trigger, put a plastic lock. It will prevent the trigger to get out from the groove.

## Step 6: The Mount

Take an iron angle and put it bellow the lower part of the mortar muzzle. This will be for the adjustable height.

Attach two iron angles on the round telephone cover, and then screw it in the back of the mortar.

Attach the two printer pieces from the paper plate on the angles, and screw them to the PC screen base.

13.

## Step 7: The Adjustable Height

Take the toilet plastic floater graduating piece (tree). Attach the hinge to the lower side and then screw it to the front side of the screen base. Screw the upper part of the adjustabble weight to the angle in the mortar muzzle.

Drill holes on the upper part of the tree, so you can graduate the cannon height with a barrette.

14.   Put the suction cups bellow the base.

Attach the keyrings on each side of the launcher for a better gripping when you charge the mortar.