Some simple pneumatics questions

Hi:

Looking to buy some pneumatics for the first time but wanted to know some items that will let us know how much to buy.

  1. Can/would you put a T after the solenoid and before the piston? Essentially like using a Y cable for two motors. Or should you have a solenoid for each piston?

  2. Have people done independent resevoirs versus chaining resevoirs together? I have seen some examples of chained resevoirs (up to 6!) but I do not recall ever seeing independent pneumatic controls from different resevoirs. Anyone try this? I guess you have a second pressure regulator and shut off switch but that is not much space/weight. Is there an advantage to this other than saving up for a guaranteed big blast for the end of the match?

  3. Are there presta valve attachments? Just a convenience to not swap out the bike pump valve at home. Presta valves tend to hold in the air better too. But it appears the part number is from Schraeder corp, the competitor of Presta.

  4. The solenoid uses the digital sensor port? Or is it like a motor port?

I’ll answer what I know… :slight_smile:

Can you? Yes.

Should you? No. You want to minimize the amount of tubing between the solenoid and the piston as much as possible. This is because all the air that fills the tubing after the solenoid is released from the system on every activation. I’m finding it a little hard to explain with words, but you could think of it this way: If the tubing after the solenoid and before the piston can contain 3 cubic inches of air, you lose at least 3 cubic inches every activation.

The solenoid uses a digital port.

Gonna do my best with my limited knowledge of the pneumatic system.

Yes, this is how my team powered two pistons simultaneously this year.

I don’t see any advantage to this, but I’m sure it would be possible. I’m sure it would just be a seperate solenoid for each system you wanted seperately powered, as well as having to fill it multiple times.

No idea on this one, I know that they use Schraeder bike valves and I assume its locked down to those.

It uses a digital sensor point, you have an off state and an on state, just like any digital value.

Thanks for the answers. If you don’t necessarily want to T the tube after the solenoid, can you use a Y cable to fire two solenoids simulataneously if digital ports are at a premium? Or is there not enough electical power to do so?

The extra air loss would be the volume of the tube times the length from the solenoid to the piston at the current pressure (and temperature). That should be compared to the original length of two tubes I guess for a fair comparison. The pistons air loss would be the same since you are firing both. (Isn’t that the specific volume??? It’s been far too long since I took Thermodynamics)

Yes, you can see our Sack Attack bot, TALUS.

I’m thinking of doing this strategy for Toss Up, you can guarantee you have air for some functions.

Not that I’m aware of, unless you attach it to the bike bump, which I believe are easy enough to find. I’m not sure about competition legality.

yes, digital sensor.

EDIT: looks like some people beat me to it. To answer the Y-cable question, I’ve never tried it. I don’t think you would run into any issues, but you would have to try it.

I have done this with two solenoids on one digital port, and it worked for a whole season. I don’t know if it worked safely though (e.g. no damage to cortex).

I don’t follow all of it (I haven’t taken thermo… maybe one of these days), but the idea of that sounds right.

The reason it uses more air is it uses a lot more tubing to get from the T to both pistons compared to extremely short tubing to go from a soloniod to a piston

You are fine to t after a solenoid, but as stated above you will lose air faster this way. With every motion of the piston all of the air in the piston and any tubing between the solenoid an the piston is discharged, so you loose the volume of the tubing as well as the volume of the cylinder; where as with a solenoid close to the cylinder, the loss is much smaller due to the shorter length of tubing. This is not a big issue as mentioned above we did it on TALUS and could last on 2 tanks for about 2 matches.

So it is fine to do just make sure to minimize the length after the solenoid as much possible and you should be fine.

I do remember someone saying that the amount of air in tubing is minute compared to a piston use and that you might not even notice but I would test that before treating it as fact.

Our team had 4 solenoids powered off of one digital port and also had no problems.

The calculations may say that the amount of air is very small, but in the real world, it actually has a big effect on the number of actuations you would get. Our team’s pneumatic lift was successful only because it had the solenoid tubes going directly to the pistons with minimal length.
Check out our last year’s reveal for more information:
https://vexforum.com/t/599d-gateway-reveal-pneumatic-lift/21777/1
It could also help with potential pneumatic lifts this year :smiley: