Bungy and Surgical tubing

[Jordan2389Diaz]

My team is trying to hook up our pneumatics system but we are wondering how power it would be? How do you hook up the surgical tubing and the bungy cords to the robot.

[Jones571]

Go to you tube and search 842 kicker and u will several great examples.

[DonRotolo]

Of course, the surgical latex tubing is not intended to be part of the pneumatic system.

The FRC Manual does explain a bit about how to connect the pneumatics. the FIRST Pneumatics Manual goes into greater detail. Both should be read before you do anything more.

As for the latex tubing, we have used it in the past as a spring to retract a mechanism, a cushion for a mechanism that hit the frame too hard, and in place of a rope or wire to kpps game pieces from falling out of the storage hopper.

This year, we tied some into a loop, and use it like a big rubber band to power the kicker. A pneumatic piston pulls the kicker back for another shot.

[Team 2811]

Originally Posted by Don Rotolo

Of course, the surgical latex tubing is not intended to be part of the pneumatic system.

The FRC Manual does explain a bit about how to connect the pneumatics. the FIRST Pneumatics Manual goes into greater detail. Both should be read before you do anything more.

As for the latex tubing, we have used it in the past as a spring to retract a mechanism, a cushion for a mechanism that hit the frame too hard, and in place of a rope or wire to kpps game pieces from falling out of the storage hopper.

This year, we tied some into a loop, and use it like a big rubber band to power the kicker. A pneumatic piston pulls the kicker back for another shot.

Yeah, I am with you on this one. The surgical tubing is not recommended or intended for the pneumatics system. It would not be a wise choice to do so, because depending on the amount of pressure that you need for your pneumatic system, the surgical tubing could expand and "pop" off of whatever you attach it to in the system.

[DonRotolo]

Not to mention it's prohibited by <R72>

[Taxi Quinn]

Originally Posted by Don Rotolo

Not to mention it's prohibited by <R72>

I dont understand what you are saying is prohibited? We are currently looking in the manual in the section you said, and we can find notheing that says anything is prohibited.

[Jones571]

Originally Posted by Taxi Quinn

We are currently looking in the manual in the section you said, and we can find notheing that says its prohibited

You may want to re read it Quinn. R72 specifically states what you are allowed to use in your pneumatic system and surgical tubing is not on there as it would be very unsafe to use in a pneumatic system. So Don is 100% correct.

[boomergeek]

Originally Posted by Don Rotolo

Of course, the surgical latex tubing is not intended to be part of the pneumatic system.
...

This year, we tied some into a loop, and use it like a big rubber band to power the kicker. A pneumatic piston pulls the kicker back for another shot.

Does your piston move during the shot? Most video examples I've seen of various pneumatic/tubing kickers show the piston moving during the shot.
If your piston moves during the shot, does it move faster than 20 inches per second?

Has Bimba (or any other actuator expert) sanctioned any conditions where a piston is "engineered appropriately" to move the piston faster than 20 inches per second?

[Ether]

Originally Posted by Taxi Quinn

I dont understand what you are saying is prohibited? We are currently looking in the manual in the section you said, and we can find notheing that says anything is prohibited.

Rule <R71> is quite clear:

<R71> To satisfy multiple constraints associated with safety, consistency, robot inspection, and constructive innovation, no pneumatic parts other than those explicitly permitted by the Pneumatic System Rules may be used on the ROBOT.

The "Pneumatic System Rules" mentioned in the above rule are those listed in Section 8.3.9 "Pneumatic System"


~

[Mike Betts]

Originally Posted by boomergeek

Does your piston move during the shot? Most video examples I've seen of various pneumatic/tubing kickers show the piston moving during the shot.
If your piston moves during the shot, does it move faster than 20 inches per second?

Has Bimba (or any other actuator expert) sanctioned any conditions where a piston is "engineered appropriately" to move the piston faster than 20 inches per second?

Dick,

This "specification" has been floating around these boards for a while now.

I'd love to find out the exact source of the 20"/sec specification. I downloaded the Bimba manual and can find it nowhere.

I calculate a 1" bore cylinder will move at about 70" per second (unloaded, 45 PSI delta with about a 2 CFPM airflow).

This was brought up in another thread. Upon reflection, my thoughts are:

1. If the cylinder is rated at 125 PSI, I would think it should be built to survive a 110 PSI delta actuation over years of use.
2. The rules state no more than 60 PSI as a working pressure.
3. Assuming that the piston is used to deflect the spring assist at a 45 PSI delta, then the effective contribution of the spring is that of a 45 PSI delta.
4. Added to the 45 PSI delta of the pneumatic system, you have an effective force of 90 PSI delta acting on the piston.

Even with pre-charged cylinders at some percentage extension to maximize speed and direct exhaust at .3 cv, I'm having a difficult time getting a dangerous material fatigue scenario for an expected lifetime of a couple of hundred two minute matches.

Like I said, I'd love to get to the source...

Regards,

Mike

[boomergeek]

Originally Posted by Ether

Rule <R71> is quite clear:

<R71> To satisfy multiple constraints associated with safety, consistency, robot inspection, and constructive innovation, no pneumatic parts other than those explicitly permitted by the Pneumatic System Rules may be used on the ROBOT.

The "Pneumatic System Rules" mentioned in the above rule are those listed in Section 8.3.9 "Pneumatic System"


~

Ether-
For the engineering rule that the maximum of 20 inches per second for piston speed, can be ignored if the piston is moving in excess of that only when powered by surgical tubing as opposed to when the movement is caused by pneumatic pressure against the piston?

I am a complete novice at pneumatics and I'm taking an educated guess that it's the seals between the piston and the cylinder that are only rated for a maximum speed of 20 inches per second, and my guess continues that it causes excessive wear is independent of whether pneumatic force or elastic force is used to drive the piston to the excessive speed.

Can anyone with knowledge of pneumatic mechanisms explain?


Thanks!

[Chris is me]

Just to be clear because someone sent me an email about it and I didn't see it in the thread, you can use surgical tubing in tandem with pneumatics (i.e. a surgical tubing power kicker pulled back with a piston), but you can't use surgical tubing to store compressed air (eg, it's not pneumatic tubing). Just in case anyone was confused, sorry if it's obvious.

[Bruceb]

If you are worried about the piston breaking itself because it hits the end stop to hard to many times then Bimba does sell pistons with adjustable air cushions at one or both ends.
Bruce

[Daniel_LaFleur]

Originally Posted by Mike Betts

Dick,

This "specification" has been floating around these boards for a while now.

I'd love to find out the exact source of the 20"/sec specification. I downloaded the Bimba manual and can find it nowhere.

I calculate a 1" bore cylinder will move at about 70" per second (unloaded, 45 PSI delta with about a 2 CFPM airflow).

This was brought up in another thread. Upon reflection, my thoughts are:

1. If the cylinder is rated at 125 PSI, I would think it should be built to survive a 110 PSI delta actuation over tears of use.
2. The rules state no more than 60 PSI as a working pressure.
3. Assuming that the piston is used to deflect the spring assist at a 45 PSI delta, then the effective contribution of the spring is that of a 45 PSI delta.
4. Added to the 45 PSI delta of the pneumatic system, you have an effective force of 90 PSI delta acting on the piston.

Even with pre-charged cylinders at some percentage extension to maximize speed and direct exhaust at .3 cv, I'm having a difficult time getting a dangerous material fatigue scenario for an expected lifetime of a couple of hundred two minute matches.

Like I said, I'd love to get to the source...

Regards,

Mike

Mike,

I'm not sure that that 'spec' is actually a spec, but instead is a 'recommendation' from Bimba.

Additionally, the speed of the cylinder is not an issue. What is an issue is the impact on the endcap of the cylinder. Consider that some teams are using upwards of a 2 pound mass on the end of a 8-10" lever and accellerating that to 50 ips and you have some serious forces trying to unseat the endcap of the cylinder.

My suggestion to all teams that are using this type of system (including elastomer assist) is to have a hard stop on your robot so that the cylinder does not 'bottom out' against the endcap.

[boomergeek]

Originally Posted by Bruceb

If you are worried about the piston breaking itself because it hits the end stop to hard to many times then Bimba does sell pistons with adjustable air cushions at one or both ends.
Bruce

Actually I'm worried that the 20 inches per second piston speed has been claimed (by multiple persons posting to CD) to have been given from Bimba Customer Support representatives.
As far as I know, no one with any expertise has stated equivocally under which conditions that it is SAFE to ignore 20 IPS guide on piston speed.

I typically choose to considered it likely to be deemed unsafe by thoughtful robot inspectors unless an expert vouches for the SAFETY of the configuration.

If leaving a piston attached to a "bow" when shooting an arrow is an engineering acceptable use of pneumatic piston, will someone with expertise in the failure modes of actuators please confirm?