Team 5236 catapult

[Hoffer5236]

Team 5236 has been hard at work on our catapult. Using two 1.5 bore cylinders on either side of the catuplt in the last videos. Also using a latching mechanism to allow the cylinders to fill up before firing. Check it out!

http://youtu.be/pzqawtl1D2Y

[thedude019]

looking great for your rookie year! There sure is plently of ways to go about a pneumatic catapult. The biggest problem was finding that sweet spot for every mounting point. In the early stages of our catapult we didnt get the ball to go very far or very high. After days and days of moving the pistons and pivot points we thought we had found a good position. it was about 5 feet away from the goal and the ball just barely made it. the following day one of the team memebers asked to move the pistons a certain way. once he did i wasnt so sure it was going to work until we fired it. from about 5 feet away the ball was tossed way over the goal. at that point we found our perfect setup. we still yet to find the correct distance but we sure know it works. Hope you all do well and have a great time.

also one of our mentors was helping us build a sping piston which consisted of one 2" bore piston. the piston would be already extended 2" to allow pressure to build and then a small lock piston would retract, letting the main piston extend at an incredible rate but still have the same amount of force behind it. I might be wong but at 60psi the piston could reach a max of 33fps whic is incredible. we saddley didnt use it as it was incredibly bulky and heavy. we still kept the design as it may be useful in the future.

[ZJ Lin]

Are you using a double acting piston in the video? If you are we found that the ball goes further if you take the fitting off the retracting port of the piston to let the air out faster during extending stroke for less resistance.

[thedude019]

Originally Posted by ZJ Lin

Are you using a double acting piston in the video? If you are we found that the ball goes further if you take the fitting off the retracting port of the piston to let the air out faster during extending stroke for less resistance.

if your port diameter on the extend side of the piston is the same as the retract, i dont think it will make a difference. the air can only leave as fast as it is put in so if the hole is equal to or greater than the extend side, you should be good. Also i wouldnt recommend elbow fittings because it causes friction and slows down air flow.

[AdamHeard]

Originally Posted by thedude019

if your port diameter on the extend side of the piston is the same as the retract, i dont think it will make a difference. the air can only leave as fast as it is put in so if the hole is equal to or greater than the extend side, you should be good. Also i wouldnt recommend elbow fittings because it causes friction and slows down air flow.

It's still an additional flow restriction, so speed will increase with the fitting removed.

[Dan.Tyler]

It's not simple volume in equals volume out.

The flow restriction changes mass flow. Specifically, it decreases it. You have to vent the same amount of mass out, but now you're doing it slower.

I will leave the real sciencey stuff for your research, but you'll have increased pressure on the exhausting side (and therefore reduced force, acceleration, and speed) with more flow restrictions.

Reference: pv=nrt and basic piston dynamics (specifically, f=A*delta_p) for the sciencey stuff.