so i was asked to make a thread were we could discuss pneumatics and i decided to involve any design stuff you all want.
so yeah i was saying that i was also weary about the pneumatics being used as a launcher. with a 2" stroke that probably wouldn’t do the trick so it would have to be lengthened by using a lever and that would decrease the strength (12lbs) and what i asked was is max force taken when the regulator is set to 100psi meaning you could only have 1 stroke or what is the deal with the max force data given on the pneumatics page under products?
The 12 lbs of force comes from multiplying the pressure out of the regulator by the surface area of the piston inside the cylinder (FYI - On a simple double-acting piston, one stroke is weaker than the other because the cylinder’s push-rod takes up space on the surface of one side of the piston).
As you use up the compressed air in the storage tank, the pressure out of the regulator will eventually fall below what you need to get a 12 lb push out of the piston.
12 Lbs is a lot of push, especially if you can get it to occur throughout a 2 inch stroke.
To get an impression of what is possible, try hitting an object that sticks out past a barrier by 1/4 inch or so. Let the hitting device be stopped by the barrier so that the hitting device only acts on the hit object for at most 1/4 inch. The hitting device can be a stretched bungee cord, or a weight on a pendulum, or some other gizmo that you can adjust.
Using the set-up I described, I’ll bet that you can send light objects, into the air, for decent distances. In the set-up I described, the mass of the hitting object (compared to the mass of the hit object) and the speed you can accelerate the hitting object to are going to be very important for how far the hit object travels. (Fast BBs will bounce off of bowling balls; and slow bowling balls striking a tennis ball won’t impart much velocity to the tennis ball.)
My hunch is that 12 to 6 lbs of force acting over 2 inches (give or take any changes made using levers/gears) can accelerate a massive-enough hitting object up to a decent speed for creating Clean Sweep artillery.
The max speed the Vex pistons will move is an important parameter. Attempting to use one to push something any faster than that top speed (without using levers/gears) will be an exercise in futility.
Finally, take a look at the videos of FRC Overdrive robots (YouTube, The Blue Alliance, Team websites) that used pneumatics. They were mostly punching the Overdrive balls, not smoothly accelerating them over the entire stroke of a pneumatic piston.
On the first day back from Dallas, we designed a scissor lift launcher. Before the addition of pneumatic power, we managed to shoot a small ball 6’ in the air and 3’ forward, but it doesn’t supply consistent power to launch multiple objects at once. As one team member put it, it works, but is completely impractical due to the amount of variance, and is good for only a few shots due to the way we designed it.
Not necessarily. If you look at the archives from FIRST from 2006 and this year, there were plenty of robots that could rapid fire balls. I would think that someone will be able to figure out a way to do it with the VEX equipment as well.
in the other clean sweep thread we talked about the unlikelyhood of this working and how at a certain point you are just uselessly adding motors due to friction. it was brought up somebody put 8 motors on 1 axle to shoot ping pong balls and never really got any results that were any good
I’m waiting for the new kit to be released before my son and I start building proofs of concepts, but the more I do the math, the less it makes sense to me that the ping pong gun wouldn’t work.
For example, I believe the wheels weigh roughly 1/4 pound each. With the half pound football, the acceleration of the football would mean a reasonable deceleration of the wheels. But with a ping pong ball, the wheels and motors shouldn’t even notice the change.
What needs to be done is three things:
Have the spacing between the wheels be correct. Both wheels need to contact at the same time.
Have the wheels get a grip on the object. With ping pong balls spongy wheels would help. With this years balls, it shouldn’t matter much.
The wheels need to spin FASTER, much faster than the motor. a 7:1 increase (84 tooth gear on the motor, 12 tooth gear gear on the wheel) should do the job and my guess is the wheels should always be spinning so that when the ball contacts them, they impart their energy on the ball. It may be that a 7:1 ratio isn’t enough though. a 7:1 increase on 100 rpm with a 4" diameter wheel is:
7100 rev/min * 1min/60sec * 4 in2*3.14 * 1ft/12in is only 25 feet per minute (depending on my math).
An airsoft gun, on the other hand shoots at roughly 150-250 feep per second.
However, we don’t want to launch the ball across the room, just over the wall.
There are enough unknowns that some proofs of concepts need to be built, but I’m not seeing anything that indicates 8 motors would be needed. I suspect it was simply the limit of the 100 rpm of the motor that was causing the issue.
It could work, but to get the shooters up to the level of efficiency that some of the FRC robots had then that would be an accomplishment! FRC Team 71 the Beast is a great example of an efficient shooter!
Picture a scissor lift with elastic bands between the middle of the diamond area, pulling the lift into an extended position. At the bottom we chained 2x pneumatic cylinders together and wired them together to fire off of one input. The pneumatics keep the elastics in check until we fire. The problem was the elastics bent the metal for lack of a better word, sideways
In all honesty, at this stage, I think the biggest reason to build something that shoots footballs, volleyballs, AND tiny soccer balls is “Because we can”.
The main advantage of a shooting design I can think of is that you can score from locations far from the wall, or have an easier time clearing defensive “wall bots.” However, I believe effective mass-shooting designs will be rare, and the game will be dominated by various designs of dumping hoppers.
We set them up in series for a 4 inch stroke. Main reason for doing this was because a team member didn’t feel like just dumping objects over, and decided launching would be a much better alternative.
