Testing and Modification

Testing and Modification

When we say and list these trial numbers, please note that while there are "three" trials on here, Harry and Derek actually tested their catapult dozens of times. These videos simply show samples of what happened.

Also, lucky for us, Derek offered to use his camera app to take high-speed video footage (8x slower speed) for the purpose of diagnosing whatever problem gets in our way.

Trial 1

Horay! It works! ...Partially.

Distance: 6 feet

One of the biggest problems we realized at first were the lack of restraints on the axle of the swinging arm. On our driveway, which sags westwards about 3 degrees, horribly threw the entire arm off center. In case this kind of angle also happens on the actual field, this should never happen. Not only does it compromise the structural integrity of the sides, it's dangerous---if that thing broke apart suddenly at launch, shards of PVC could scatter rampantly at unsuspecting victims.

Another thing that could have been off was the length of the rope. Notice how the counterweight's swing causes the arm to stall from 0.7 seconds to 1.0 seconds. It's as if the rope actually tries to force the projectile backwards during that time!

Our last possible reason we came up with was the lack of weights latched onto M1. After a few calculations involving the speed of the ball at launch, we've calculated the initial velocity to be just 5.3 meters per second, far short of the 10.3 meters per second we need. So, perhaps strapping random metal objects rigidly onto the counterweight will help? Let's find out.

Trial 2

There are quite a few modifications that our catapult underwent before the second trials:

• Cardboard/PVC sides were added onto the axle of the swinging arm to prevent excess swaying from side to side

• Our rope is only an inch shorter than it used to be---a series of unrecorded tests oddly shown that the rope length was just where it has to be

• A whole bunch of random metal objects were strapped to the counterweight via webbing and Harry's awesome knot tying skills.

<--We do what we must because we can.

So, did anything change?

What a disappointment. The release mechanism flopped.

Distance: None

The tests in Trial 2 were mind-boggling and confusing due to how inconsistent our catapult seemed to be. Sometimes our projectile would launch, sometimes it wouldn't. This video illustrates such inconsistency:

Distance: 19 feet, None

Harry and Derek argued on exactly what the cause of the misfires seemed to be in the first place. Derek suggested trying different angles for the projectile to launch from within the sling, while Harry wanted to duct tape over the hole near the top of L2. Either way, the debate raged for hours and the answer seemed indecipherable until a new video had to be taken just to work for the projectile motion sketches for this blog; it could have been done without it, but we tried it again for kicks. No one wrapped the sling up, nor was there any duct tape, so both thought the catapult would fail. BUT THEN...

Trial 3

By now, we painted our catapult orange and blue Portal colors.

WOOHOOOOOOOOO!

Distance: 28 feet

Neither one of us knew exactly what we did right at first, but we soon figured out that the secret was NOT spinning the sling in knots. Such a process prevents the releasing rope from flipping shut. As for duct tape, it just seemed unnecessary to add at that point. Don't fix something that works perfectly.

Excited, we ran run after run after run to make sure we're consistent this time.

Distance: 32 feet

Distance: 25 feet

Distance: 29 feet

At this point, Harry and Derek decided to stop construction; we had already done enough and were confident that our catapult would earn an excellent grade.