faster release

[ravichauhan]

how can we exhaust the air faster from our piston. it is slowing our kicker down. please help. thanks

[Ed Law]

Originally Posted by ravichauhan

how can we exhaust the air faster from our piston. it is slowing our kicker down. please help. thanks

What solenoid valve are you using? What size cylinder are you using (bore and stroke)?

[ravichauhan]

1.5" diameter, 8" stroke. smc sy3240 valve

[Ed Law]

Here are three options you can try.

1) Use smaller bore size if it creates enough force for you. Speed is more important than force here. There is less volume to fill and the piston will come out faster.

2) Add a spring (torsion/compression/extension/air/surgical tube) to help the piston extend.

3) Push closer to pivot point with less stroke. That will magnify your speed depends on how close you put to pivot point. It also saves air but you get less force on the ball.

Hope this helps.

[ravichauhan]

thank you

[Jones571]

Teams have also had luck with running more then one valve in paralell to increase speed. Other like 842 who we got the idea from preload the cylinder holding it back with a gate latch then release the latch to fire.

[dtengineering]

You have to consider the "bottleneck" in the system. There are some intentional bottlenecks imposed by the FRC rules that are specifically intended to limit the power (and potential hazard) of pneumatics.

One of the bottlenecks is the regulator. To de-bottleneck the regulator, consider putting one or two clippard air reservoir tanks on the low pressure side of the system, in addition to one or two on the high pressure side. That way, when you need 60psi air FAST, you don't have to wait for it to pass through the regulator.

The next bottleneck is the tubing. Consider pneumatic tubing to be similar to electrical wire... shorter runs makes for less resistance. So keep those clippard tanks close to the valves, and keep the valves close to the cylinders.

The valves also present a bottleneck... but you can put them in parallel if you want to debottleneck that stage.

Finally you have a bottleneck at the fitting. Even if you have more valves in parallel than you need, you can only pass air so quickly through the tubing and fitting attached to the cylinder. One way around this is to, as previously mentioned, use multiple smaller cylinders. That way you have many fittings (and many pieces of tubing and possibly many valves) in parallel. Just like a parallel circuit in electronics can deliver a higher current, a parallel circuit in pneumatics can deliver greater air flow.

I also believe there was a Q&A asking if you could use one of the brass couplings to connect a valve directly to the cylinder, which would debottleneck the fitting stage somewhat... but do check the Q&A forums on that. Perhaps a better way to get around that would be to partially retract the cylinder, latch it in place, and then pressurize the cylinder. There is another thread discussing the optimum "precharge" ratio, somewhere between 30-40% sounds about right. This way when you release the latched cylinder the pressurized air is already stored inside the cylinder and has passed by all the bottlenecks. 1726 posted some good photos of their trackball launching design a couple years ago that encouraged us to pursue this route, with good success.

Finally, consider that if you don't need to use air to retract your cylinder, that you can leave one end of the cylinder open to atmosphere. That way there is NO bottleneck on the venting side.

I haven't done calculations to determine which of these is the most significant step, but collectively they all add up to limit the speed that your pneumatics can retract or extend. In our experience using two 3/4" cylinders with latex tubing to improve retraction force (The final design will use 4 3/4"x4" cylinders in parallel, giving us a force equal to that 1 1/2" cylinder, but with four times the air flow rate), we found a significant improvement in performance when using two valves rather than one, and putting a clippard tank immediately upstream of the valves.

Good luck, and have fun,

Jason

[Ether]

Originally Posted by dtengineering

...
In our experience using two 3/4" cylinders with latex tubing to improve retraction force
...

Did you mean to say "retraction" here?


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[dtengineering]

In our design we retract the cylinders to kick. So we wrap just enough latex tubing around the clevis and cylinder ends so that the cylinder can just barely extend all the way.

Then we switch the valves and whammo!

Jason

[Daniel_LaFleur]

Originally Posted by dtengineering

In our design we retract the cylinders to kick. So we wrap just enough latex tubing around the clevis and cylinder ends so that the cylinder can just barely extend all the way.

Then we switch the valves and whammo!

Jason

Jason,

I'd be interested in why your team chose to retract the cylinder to kick when cylinders typically have less pull force than push force due to the area that the rod takes up.

[martin417]

Originally Posted by Daniel_LaFleur

Jason,

I'd be interested in why your team chose to retract the cylinder to kick when cylinders typically have less pull force than push force due to the area that the rod takes up.

I would guess that they are using the surgical tubing for the force, and the cylinders to stretch the tubing. You can get more stretch force on the extend side.

[Daniel_LaFleur]

Originally Posted by martin417

I would guess that they are using the surgical tubing for the force, and the cylinders to stretch the tubing. You can get more stretch force on the extend side.

Force is the pressure x area of the plunger. With the rod in place you will get less force, and thus be able to strech the tubing less.

I'm just wondering if there isn't some other design consideration that validates why he'd pull instead of push with the cylinder.

[Ether]

Originally Posted by Daniel_LaFleur

Force is the pressure x area of the plunger. With the rod in place you will get less force, and thus be able to strech the tubing less.

I'm just wondering if there isn't some other design consideration that validates why he'd pull instead of push with the cylinder.

See Jason's post #9.

He does push. They extend the pistons to stretch the latex tubing to arm the kicker.

Then they release it to kick.

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[IndySam]

Originally Posted by Daniel_LaFleur

Force is the pressure x area of the plunger. With the rod in place you will get less force, and thus be able to strech the tubing less.

I'm just wondering if there isn't some other design consideration that validates why he'd pull instead of push with the cylinder.

We are pulling instead of pushing because it fits in the robot envelope better. Also the real need is speed not power.

[Ether]

Originally Posted by IndySam

We are pulling instead of pushing because it fits in the robot envelope better. Also the real need is speed not power.

Yes, Speed is King, as long as the kicker has sufficient mass, or force at the end of the stroke, that it doesn't "bounce off" the ball, in which case you wouldn't get much ball speed.

For example, try striking a bowling ball with a bamboo stick. You can swing that stick as fast as you want, and the ball is not going to do much.

Now try hitting that bowling ball with an 8 pound sledge. You'll be swinging the sledge a lot slower than the stick (less speed), but you'll get a lot more action (assuming you don't break the ball!).

So, it's a balance between speed and force and mass. Take high-speed video of your kicker in action. If the kicker doesn't "follow through", you need more mass or force.


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