3336 Catapult Prototype

[CheerlessBear]

My team was able to make an effective catapult by using surgical tubing and 80-20 and that worked fairly well.

[Physicguy]

Originally Posted by CheerlessBear

My team was able to make an effective catapult by using surgical tubing and 80-20 and that worked fairly well.

I would have to agree...speaking from experience trying to use pneumatics to drive your catapult may not be the best idea. You may want to explore a combination of surgical tubing and pneumatics would probably give a better result. Our team is trying a pure motor driven catapult.

[CheerlessBear]

My team originally tried pneumatics and we couldent achieve the speed we needed so we tried other designs. But we have not tried purely motor driven may I ask how you are implementing it?

[Aroki]

Originally Posted by CheerlessBear

My team originally tried pneumatics and we couldent achieve the speed we needed so we tried other designs. But we have not tried purely motor driven may I ask how you are implementing it?

We had success with our purely pneumatic catapult prototype. The key is using a lever and pulling down on the opposite side of the catapult instead of pushing up; this gives it more speed and with pneumatics you have power to spare.

[MichaelBick]

Originally Posted by Aroki

We had success with our purely pneumatic catapult prototype. The key is using a lever and pulling down on the opposite side of the catapult instead of pushing up; this gives it more speed and with pneumatics you have power to spare.

Based on how pneumatic works, they should push and pull at the same speed. You are likely getting better results because you are pulling closer to the fulcrum then you were pushing or because your pneumatic cylinders are acting at a better angle.

[Brian C]

Originally Posted by MichaelBick

Based on how pneumatic works, they should push and pull at the same speed.

This may not actually be correct.

There is more pushing force in the pneumatic cylinder as there is more surface area on the piston being pushed by the air. There is less force when retracting (pulling) due to there being less surface area on the piston face. This is due to the shaft attached to the piston.

While this may not sound like much it can be significant depending on what you are trying to accomplish.

[MichaelBick]

Originally Posted by Brian C

This may not actually be correct.

There is more pushing force in the pneumatic cylinder as there is more surface area on the piston being pushed by the air. There is less force when retracting (pulling) due to there being less surface area on the piston face. This is due to the shaft attached to the piston.

While this may not sound like much it can be significant depending on what you are trying to accomplish.

I didn't think about that, but you are correct. Regardless it is unlikely that Aroki's success is correlated with pulling instead of pushing but rather the angle and position that the pneumatic cylinders are pulling at.

[DRH2o]

Originally Posted by MichaelBick

I didn't think about that, but you are correct. Regardless it is unlikely that Aroki's success is correlated with pulling instead of pushing but rather the angle and position that the pneumatic cylinders are pulling at.

However -- Pulling is going to gain a great deal of speed due to the volume needed to fill the cylinder is reduced. I understand you can gain the same speed pushing by introducing the exhaust from the solenoid back in with the input air -- have not tested it, but will tomorrow.

[MichaelBick]

Originally Posted by DRH2o

However -- Pulling is going to gain a great deal of speed due to the volume needed to fill the cylinder is reduced. I understand you can gain the same speed pushing by introducing the exhaust from the solenoid back in with the input air -- have not tested it, but will tomorrow.

Or you can push with smaller cylinders

[Aroki]

I worded my response earlier pretty poorly, I wasn't talking about the difference in speed/power between a cylinder going in or out. I was merely making a point about using a lever to account for the slower speed of pneumatic cylinders as opposed to elastics or springs. The ri3d and several other places that said pneumatics don't work for shooting since they aren't fast enough were either placing the cylinders to far from the fulcrum or trying a punch, where the slower speed is a huge problem.

[thursam]

Here's the intake system, as requested;

http://www.youtube.com/watch?v=2T0Mk...eature=mh_lolz

[Hoffer5236]

Originally Posted by Aroki

We had success with our purely pneumatic catapult prototype. The key is using a lever and pulling down on the opposite side of the catapult instead of pushing up; this gives it more speed and with pneumatics you have power to spare.

We tried putting our cylinders on the opposite end of the fulcrum, but it made our length too significant to consider it being an option. Instead, we put the pistons (two 1.5in cylinders) on the same side as the basket with the ball. This decreased our length and seemed to give us some more power because pistons push with more force. The only problem that we ran into was that when the pistons were beginning to push up, the angle they were pushing at decreased any added force we had from leverage, giving us a much slower start.
This video shows our progression with the catapult.
http://youtu.be/r-9v9loC2As

[BBray_T1296]

Originally Posted by CheerlessBear

My team originally tried pneumatics and we couldent achieve the speed we needed so we tried other designs. But we have not tried purely motor driven may I ask how you are implementing it?

May I direct you to the Robot in 3 Days? (Specifically Team BOOM DONE)