pneumatics or motors?
 

In this year's game you can either. My team's inexperienced with pneumatics and more experienced with using motors. But using pneumatics this year seems more beneficial.
What are the pros and cons of each for this year's game?

For your ball shooting mechanism?

Re: pneumatics or motors?
 

Using pneumatics vs motors in what aspect? We need more detail before we can comment.

Re: pneumatics or motors?
 

Agreed. While I wouldn't use pneumatics for certain applications (like driving my drivetrain), I would definitely use them over motors in other applications (such as linear movement).

Re: pneumatics or motors?
 

Don't be lulled into false hope with the number of available motors. Add too many or have several running at the same time can cause you to draw the battery down to critical levels. Remember that the Crio will automatically disable all outputs when the battery voltage falls to 5.5 volts. It will generally reboot if the battery voltage falls to 4.5 volts for a short time. You are being given more motors to choose from for your particular design. Use them wisely.

Re: pneumatics or motors?
 

ahh sorry guys. My bad. What I mean: pneumatics or motors for shooting?

Re: pneumatics or motors?
 

Depends on your design. In my opinion, based off of tons of research, pneumatic rams would need reloading, and would have not as much power as motor powered shooters. For shooting basketballs, just use motors.

Re: pneumatics or motors?
 

I didn't see a possible way to use pneumatics to shoot consistently. You have to have a huge amount of force just to get the ball to move. My team tried it with a tennis ball earlier in the year to test the idea of shooting anything using pneumatics, and it barely made it 10 feet. That was with all the air pressure they wanted to use. They didn't have a tank restriction and didn't use just 60 working psi. It was unimpressive. I could be wrong, and there could be a genius way to use them. But right now using a baseball pitching design seems to be the only viable option to keep a consistent shot while it being reasonable in the sense that you can do it more than once.

Re: pneumatics or motors?
 

I just don't see any way that you can flow enough air to move a piston fast enough to launch a ball any impressive distance. For close up action that may work fine, but the maximum valve port diameter restrictions in the rule book just seem too restrictive to do anything worth while.

Re: pneumatics or motors?
 

Don't underestimate what's possible with pneumatics. Watch the robot in the lower right in the following video kick soccer balls pneumatically. http://www.youtube.com/watch?feature...4VhtI#t=16 0s

Re: pneumatics or motors?
 

That was fully pneumatic? Wow, I always figured it was surgical tubing/etc. Care to elaborate? That was (albeit entirely characteristically) an amazing machine.

Re: pneumatics or motors?
 

Using a pneumatic cylinder to push balls directly will be disappointing, given the equipment legal on an FRC robot.

In Breakaway, many teams kicked the soccer ball using latex tubing to power the kicking 'leg, and then used a cylinder to reset the 'leg'. A latch held the 'leg' in place until the driver decided to kick again.

In Aim High, the more successful robots used a spinning wheel, like a baseball pitching machine uses, to launch balls. A well-designed mechanism was extraordinarily repeatable, but that is difficult to actually do, since the wheel wants to slow down as its momentum gets put into the ball.

Don't be afraid of pneumatics, but please read the rules very carefully to make sure your robot uses ALL of the safety equipment properly. This includes the 120 PSI relief valve*, the pressure release valve, the pressure switch**, the primary regulator, both pressure gauges, and the cRio and a Spike to control the compressor.

*This is supplied uncalibrated, be sure to calibrate it before use
** This is wired to a digital input of the digital sidecar. That signal is used by the cRio to control the Spike relay controlling the compressor.

Re: pneumatics or motors?
 

There are some details in this thread http://www.chiefdelphi.com/media/photos/35118

Re: pneumatics or motors?
 

If you want to see pneumatic shooting at its best, check this out:

http://www.youtube.com/watch?v=cdzpC...&lf=plpp_video

close up CAD rendering of the robot:
http://www.teamtitanium.org/images/09botfull.jpg

I got to see this robot up close when it was in use for Lunacy, it was a really beautiful job!

Re: pneumatics or motors?
 

In Aim High, pretty much any team that did throw balls used a motorized wheel, like the aforementioned pitching wheel. It did have the tendency of slowing down the wheel, but if you give it a second or two to ramp back up to speed, I think it'll still be faster than drawing back a pneumatic cylinder to reload.

If you want to use pneumatics, my suggestion would be to use a "catapult" type arm to throw the ball, and place the pneumatic cylinder between the fulcrum and the load of the arm. Think how a hammer works driving a nail... the fulcrum is the butt of the handle, the arm swinging it is the arm (located up more on the handle), and the load is the head driving the nail with a lot of speed.

Re: pneumatics or motors?
 

Neither of you are thinking outside the box ;)

Take a 12" cylindar. lock it 1/2 way (mechanical lock like a fence latch). pressurize the cylindar. release the lock and see how fast the cylindar reacts and how far you shoot the ball.

oh, I'd put a hard stop on the rod so you dont damage the cylindars end cap ;)

Re: pneumatics or motors?
 

I dont think that will work very well Daniel.. We tried something like that on the 1st day, and the output port limits the speed at which the cilinder will react.. Very unimpressive.. Now if you could open one side with a huge port, that would be a different ball game..

Re: pneumatics or motors?
 

Check to see if quick release valves are legal in this game. We used one on a single cylinder in Breakaway and could shoot well over 30' if we had a good angle.

Re: pneumatics or motors?
 

In Breakaway, we scored from the far end of the field in autonomous and during the matches using a pre-pressurized, gate-latched pneumatic cylinder, and lots of surgical tubing to assist with kicking the soccer balls.

The cylinder re-tensioned the surgical tubing, was latched in the closed position, pressurized to 60psi (a force of ~180lbs), and another much smaller cylinder released the gate latch. Tremendous forces and speeds! That design helped our alliance win the 2010 Colorado Regional. With 120psi on the air cylinder our kick tests on soccer balls have gone about 55'.

If we wanted to kick a short shot, like if we were on offense, then we fire the solenoid to kick, and then immediately reverse it. We actually had good distance control, depending on how long of a delay we used between the extend and retract we had decent control of the stroke.

Re: pneumatics or motors?
 

That's exactly what our team did (servo release instead of pneumatic). Except our balls would go about 10 feet. Probably just "rookie mistakes"

Re: pneumatics or motors?
 

In 2008 we had a 2-stage pneumatic launcher that would throw the ball clear over the bars through direct actuation (no mechanical advantage or spring assist), something we were told was impossible. The trick? Use multiple 1/2"-3/4" pistons, each with its own solenoid valve. Those pistons will respond VERY quickly.

Re: pneumatics or motors?
 

The design of the shooter is very important, but what I, personnally, think should be focused on more, is the quality of the build. Even if you have an amazing design, lousy build quality can cripple any team. However, if your design isn't so good, a well-build mechanism can make up for lost range with upsides, like consistency.

Re: pneumatics or motors?
 

What about using pneumatics for the ball lifter (that carries the balls into the shooter from a ball gatherer)? In 2006 it seems like a lot of the more successful teams used rollers and belts in a conveyer system to carry the balls. We were wondering if we could use pistons to literally push the balls up into the shooter. All I know is that our rookie year in 2006 we tried to use an auger and failed epically. :)

Re: pneumatics or motors?
 

Arghhh, so many mentions of "pistons" in one thread! Sorry guys but that's one of my pet peeves, the correct term is cylinders.

Re: pneumatics or motors?
 

Tell that to the pneumatic shooter we have in our lab ;)

IndySam is right (mostly) ... although I prefer the term 'Pneumatic Linear Actuator'

Re: pneumatics or motors?
 

I'm toying with the idea of directly propelling the ball with compressed air: a cannon design. Think compressed air potato cannon. A quick calc for a cannon shooting the ball 25' would only require about 2 psi in the accumulator (air reservoir). This does not account for leakage around the ball and that may be a "show stopper". The calcs were based on a cannon only 8" long (same as ball diam) which would allow easy front loading.

Re: pneumatics or motors?
 

Take a look at the Cv of the solenoid valves we're allowed to use and determine if you have a prayer of flowing enough air through it. I have a feeling that might be your limiting factor.

Re: pneumatics or motors?
 

Thanks James for the heads-up. Compressed air limits are:

• Max supply pressure = 60 psig
• Solenoid Cv = 0.35
• Compressor capacity = 1.05 SCFM (says CFM in the rules ???)

My pressure required at the cannon will be less than 10 PSI = 50 PSIG dP. If I'm doing the air Cv calc right, I get between a bit over 10 SCFM.

I'm also looking at high pressure blower feasibility (~ 8 PSIG). Any thoughts on that legality?

Re: pneumatics or motors?
 

My math says that filling that volume chamber (8in diameter, 8in length, right cylinder) at 10CFM will result in an exit velocity of less than 0.5ft/s. No doubt this equation is simplistic, but it shows that the idea is two orders of magnitude off of what I consider a good exit velocity (50ft/s is what we're 'shooting' for) and I would abandon the idea as unfeasible, pneumatic component legality aside.

Hope this helps guide your design decision.

Using a fan or blower may work, and I don't *think* it would be illegal (I AM NOT THE GDC), but I don't think that it will efficiently transfer kinetic energy to the ball. I spent most of my junior year of college building and running turbo-machinery experiments, so this is a 'semi-expert' opinion, take it for what its worth. A decent, maximized, blower efficiency is usually around 80%, and I bet you won't be operating near this over a shot cycle given that the ball is accelerating away and therefore your flow rate is changing rapidly. I don't think the work of sizing motors, blower, housings, and a lunch tube to work optimally will be worth all of the inevitable efficiency sacrifices you'll be making.

Re: pneumatics or motors?
 

The 10 CFM fills an accumulator (reservoir) until charged to about 2-3 PSI. The compressed air is released directly into the end of the cannon; like a potato cannon. The air is released very fast and the 2 psi acts against the 50 sq.in. surface of the ball = 100 lb force at initial release. My calcs say I need about 15 ft-lb energy to accelerate the ball to about 31 ft/sec. The size of the accumulator will determine the final exit pressure on the ball. Of course leakage around the ball is a big variable.

Re: pneumatics or motors?
 

The valve you would need to release that pressure still would need to be higher than 0.32cv (not 0.35) correct? Blowers are not illegal when driven by legal motors only.

Re: pneumatics or motors?
 

Ah, I misunderstood.

I still think that you should check to see if the valve/hoses will flow enough air fast enough to do what you want. Though I'm still not convinced that an air-cannon is legal.

Re: pneumatics or motors?
 

that plus if you use 4 1/2 inch cylinders vs 1 2 inch cylinder you have the same force but 4 times the flow. when you need speed and force in pneumatics use multiple small cylinders in parallel. and using a mechanical stop to allow the cylinders to charge like daniel said makes a huge difference.

here is a example of a multiple cylinder launcher.
http://www.youtube.com/watch?v=QeQSGmFnKAE


here is another example
http://www.youtube.com/watch?v=0c6mym04OGs


both of those shooters used multiple cylinders with a mechanical stop the breakaway bot used a door latch type mechanism and the overdrve bot had a delta p of about 1.5 psi so the pistons would deform into the ball until there was enough force to break the vacuum.
which with that amount of surface area was about 200-300 pounds

Re: pneumatics or motors?
 

OK. Lets go through this:

1: How do you charge the accumulator without using a valve(0.32CV) between the accumulator and the cannon?

2: In order to release the air that fast you would need either a vane valve or sprinkler valve. Both have CVs too high for FIRST.
3: Consider your mass flow. As the valve is opened the air starts to flow and pressure begins to build in the cannon (I'll ignore leakage around the ball, which you'd want to lower frictional forces). When the pressure gets to ~0.15PSI (12 oz acting on an 11 oz ball) the ball will start to move up the cannon.

4: Pressure will remain ~ 0.15PSI as the air fills the, now additional, volume created by the ball movement. giving you only .75LBf of the 15LBf that you need.

My guess is that the ball never leaves the cannon, as the leakage around the ball will probably have a higher CV than the CV of the valve used.

Re: pneumatics or motors?
 

Good point, but the release mechanism isn't a solenoid and would have to be exempt form the Cv limitation. Maybe low pressure systems (< 5 PSI) won't be considered "compressed air" rather "high energy fan system". :]

I'm also thinking of charging the cannon directly by the blower (no reservoir) and just tuning the blower ON/OFF. Modulation of the force would be done by varying the voltage on the blower motor.

At any rate, I'll be protoyping this today and let you know if the performance makes it worth pursuing.

Re: pneumatics or motors?
 

Dad,
Unfortunately, any pneumatics are inspected under the pneumatics rules regardless the pressure. Blowers on the other hand will be looked at for electrical, motor, mechanical and safety parts of the inspection checklist. Of particular concern would be exposed moving parts. They are pretty much handled the way ball launchers would be. We don't want fingers getting damaged or worse so things do need shields when they pose a threat to humans.

Re: pneumatics or motors?
 

Hi Al,

Thanks so much for the clarification. This makes sense as any stored energy from CA is a potential danger and following a standard CA safety standard is required.

Much appreciated,

Craig