Usign a 2-1/2 bore, 24" stroke pneumatic cylinder.

[indieFan]

My team is using a 2" cylinder with a 24" stroke to hang our robot, but we're having problems retracting and lifting.

We were using a single air tank at the first competition we went to. It was found that gently nudging the robot at the start of retraction seemed to get it going.

We then added two more air tanks and checked the gauges immediately after we extended to see if that was the issue. The high gauge read about 50psi, if I remember correctly, the low was 50psi for a split second and then back to 60psi. We did not have the chance to test actually hanging with this set up.

We took our robot to a practice field, but our controller was not working correctly. To test our pneumatics, we tried to manually trigger the solenoid. This did not produce the results we were hoping for; however, it is unclear if this was due to the manual triggering or a pneumatics issue.

Our robot weighs 77lbs with battery (and I believe bumpers).

My questions:
1. How much time does a pneumatic of this size take to refill?

2. Will the 2nd and 3rd air tanks mitigate the time in question 1?

3. Is there anything else that can be thought of in relation to pneumatics that might need troubleshooting?

Thanks for any help,
indieFan

[DanielPlotas]

If you use constant force springs in line with your cylinder, you can use a smaller diameter cylinder. There's a voucher for six free springs from Vulcan in the KOP.

[CloakAndDagger]

We use two 1 3/4" BIMBA cylinders, and hang by the rods. We haven't had any pneumatic problems yet

We have 5 air tanks also, and run it off of two solenoids and two regulators. The solenoids each lead to both cylinders, and are slaved together. We do this because the internal diameter of one solenoid it too small to facilitate rapid airflow

[hrench]

Originally Posted by DanielPlotas

If you use constant force springs in line with your cylinder, you can use a smaller diameter cylinder.

This constant-force spring thing seems like a good idea, but it means that it takes more pressure (equals force) to extend your rod initially. Which means it uses lots of your stored air reaching up for the bar.

I wonder if it would be better to actually put a pressure regulator between the extension-end of the air cylinder and the air solenoid valve and just extend at say 5-psi? If you can still reach up very fast but not actually pressurize the extending side of the air system to a very high number, you'll save all of that stored pressure in your tanks for the lifting-retracting stage.

We built a robot-lifting cylinder in our prototyping at the start of build--used a 2" dia--which should've been able to lift 176 lbs, but with a 120lb robot, battery, bumpers and the added friction of dragging the bumper up the wall, it didn't move very well at 60 psi and was very slow after the air in the storage tanks was used up.

I hope you can make it work. good luck.

Also note,

I know these equations are easy, but if you need a quick-reference for how much force each bimba-sized cylinder makes at 60 psi for pushing and pulling, I've created this easy chart.
https://docs.google.com/spreadsheets...it?usp=sharing

[pfreivald]

Originally Posted by hrench

This constant-force spring thing seems like a good idea, but it means that it takes more pressure (equals force) to extend your rod initially. Which means it uses lots of your stored air reaching up for the bar.

Unless you add in the additional pressure regulator, you're extending at 120 psi anyway...so add ~75 lbs (or however much) of constant force springs, extend at full pressure to extend them, then let them help you on the way down. The pneumatics will be smaller, so you'll be saving air on the up and down strokes (which might obviate the need for the additional regulator to bring down the extension pressure.)

Some math (maybe some graphs with an eye toward that 150-lb requirement) should help you determine an optimal* amount of spring vs. bore.

*optimal, of course, depending on which resources you're trying to preserve.

As another idea, consider constant force springs that are already extended along the body of the cylinder, but don't lock in to the rod until it's fully extended--so you don't have to push against them at all, but they'll help you pull it back. Might require some cams, spring-pins, or whatnot.

[FrankJ]

Originally Posted by pfreivald

Unless you add in the additional pressure regulator, you're extending at 120 psi anyway...

Your stored air pressure is a max of 120 PSI. Most pressure switches are shutting off at around 115 indicated. Your working air pressure shouldn't ever be above 60 psi.

[Jaxom]

Originally Posted by CloakAndDagger

We have 5 air tanks also, and run it off of two solenoids and two regulators. The solenoids each lead to both cylinders, and are slaved together. We do this because the internal diameter of one solenoid it too small to facilitate rapid airflow

That's by design; see rule R17 C. Unless I'm misunderstanding your post you need to take a good look at R90.

[hrench]

Originally Posted by pfreivald

Unless you add in the additional pressure regulator, you're extending at 120 psi anyway...so add ~75 lbs...

I'm sure as FrankJ mentioned, you mean that the cylinder is operating at running pressure, 60 psi (or less depending on your robot), not 120 or 75, but I say that the pressure inside the cylinder while the piston is moving is definitely Not that high.

What I mean is that the piston will begin moving immediately when the pressure on the pushing-side of it has exceeded the resistance-- friction loads, weight and if you have them, springs. The piston will continue to move at very low pressure staying just ahead of the friction and load until the time that the piston reaches then end of travel. Only then does any real pressure build up inside the cylinder on the 'up' side of the piston.

So if you have a pressure regulator between the valve and the piston, you'll be able to limit the pressure on the 'up' side of the piston to conserve air. Lots of it actually. You'll still need all of the pressure you can muster to lift the robot, so you can't put the regulator before the valve or anyplace that would limit the 'down' pressure.

So if you don't have springs to overcome, you'd be able to extend the lifting hook under very low pressure, like 5 psi (a 2.5" dia has 4.9 sq inches, at 5 psi is close to 25 lbs force)

Originally Posted by pfreivald

As another idea, consider constant force springs that are already extended along the body of the cylinder, but don't lock in to the rod until it's fully extended-.

Yes, this is a very interesting idea too. Though I would rate it as 'difficult'. Of course there are teams that completely lifted the robot with springs that were already storing energy too (I saw 1619) So in this iteration, if you used an air cylinder, it would only need to get the hook up to the bar. Could be tiny.

[pfreivald]

Yeah, yeah, yeah. Fingers before brain and all that.

60 psi working, not 120.

[CloakAndDagger]

Originally Posted by Jaxom

That's by design; see rule R17 C. Unless I'm misunderstanding your post you need to take a good look at R90.

Not seeing a subsection of any type within r17, so not sure about that one

In regards to r90, I'm not sure that a solenoid actually qualifies as a valve, because (As I understand it) a valve contains or limits pressure, whereas a solenoid simply directs it one direction or another, without limiting it in any way.

Based on that, we are basically just connecting two pneumatic tubes together.

I'll check on that with our mentors in our meeting tonight though- I am but a humble programmer, so it is very likely that I'm incorrect on that.

[GeeTwo]

Originally Posted by CloakAndDagger

Not seeing a subsection of any type within r17, so not sure about that one

I'm sure that was supposed to be R77C:

The only pneumatic system items permitted on 2016 FIRST Robotics Competition ROBOTS include
the items listed below.

• .
• .
• C. Solenoid valves with a maximum 1/8 in. NPT, BSPP, or BSPT port diameter

Originally Posted by CloakAndDagger

In regards to r90, I'm not sure that a solenoid actually qualifies as a valve, because (As I understand it) a valve contains or limits pressure, whereas a solenoid simply directs it one direction or another, without limiting it in any way.

Yes, a solenoid valve is a valve. Valve outputs on an FRC robot may pass to the input of another component (or components), or vent to atmosphere.

[hrench]

Originally Posted by CloakAndDagger

... I'm not sure that a solenoid actually qualifies as a valve, because (As I understand it) a valve contains or limits pressure, whereas a solenoid simply directs it one direction or another, without limiting it in any way.

I've been cringing at this terminology/usage all year.

A 'solenoid' is a controlled magnetic field. We use a solenoid to move a piece of iron magnetically that operates an air valve.

I sometimes refer to them as 'solenoid air valves' just so the people that call them 'solenoids' will understand, but yes, they are definitely air valves.

And if you have two plumbed together on your robot to operate two cylinders, I encourage you to separate them before your next inspection.

[kstl99]

Originally Posted by CloakAndDagger

In regards to r90, I'm not sure that a solenoid actually qualifies as a valve, because (As I understand it) a valve contains or limits pressure, whereas a solenoid simply directs it one direction or another, without limiting it in any way.

They are solenoid valves.
In 2010 when you had to kick a soccer ball we (1922) used 4 solenoids all plumbed to one cylinder and had one of the strongest kickers around, strong enough that Dean Kamen was examining it at GSR. The next year was the first year that was not allowed. We kinda think we caused this rule.

[CloakAndDagger]

Alright, things were cleared up for me at our meeting: They each route to separate cylinders, completely my bad on that one.