pneumatic air cylinder bore.

[JohnC]

Team Lone Star / Bounty Hunters / Boom Bots is trying to upgrade a bot that uses Slam Specialties Airbags.

Are there any composite tubes off the shelf other than from Australia that can be used as replacement for aluminum Pneumatic tubes?

Our design is a power multiplying 3 stage design 8" in diameter with a 3.5" extended length.  The tube would have to be extremely smooth on the inside and structurally strong in the vertical plane.

We can handle machining the end caps but if there are any suggestions for pistons and tubes (off the shelf) I would be very interested.

The attached is an example but our design would most likely have input and outputs per cylinder not just a vent.

 

Thanks

JC

[John Kimball]

As with any design that requires precision and specific loads, an engineering analysis and design is critical to prevent failure or potential safety concerns. It's understood that in your world, the damage mitigation is mostly centered around impact and collision (with the ground and other kinetic energy whirling weapons), which makes it even more critical to design properly. Most composite cylinders that are used for hydraulic pumps use a somewhat flexible, but compliant seal on the piston to build pressure without allowing leaking. Most composite tubes are made on polished mandrels, so they may be smooth enough, but if the mandrel is old, it may introduce some scoring on the interior. 

Long story short, It's not wise to use an off-the-shelf solution unless it's specifically designed for the internal pressures required. Do you know what those loads are?

[JohnC]

1 hour ago, John Kimball said:

As with any design that requires precision and specific loads, an engineering analysis and design is critical to prevent failure or potential safety concerns. It's understood that in your world, the damage mitigation is mostly centered around impact and collision (with the ground and other kinetic energy whirling weapons), which makes it even more critical to design properly. Most composite cylinders that are used for hydraulic pumps use a somewhat flexible, but compliant seal on the piston to build pressure without allowing leaking. Most composite tubes are made on polished mandrels, so they may be smooth enough, but if the mandrel is old, it may introduce some scoring on the interior. 

Long story short, It's not wise to use an off-the-shelf solution unless it's specifically designed for the internal pressures required. Do you know what those loads are?

Well I can say that failure is expected but not the preferred mode of operation.

I would assume the internal air pressure not to exceed 200psi of air as I am trying to get away from the 400 psi pressures of the air bags.

That would put each 8" tube at approximately 9000 lbs assuming a 1-1.75 shaft diameter. 

ideally safety parameters don't need to be 3x but thats what I strive for. Each "section" would have an aluminum or composite end plates (or combination) secured on 4 sides. 

Its likely I don't have the weight to do it but the present bags are approx. 11lbs with the end plates being another 7-11lbs each. 

So right now my system is approx. 25 lbs.  Side loading shouldn't be an issue as a linear guide is employed to keep the shaft perpendicular to the base.

(sorry I have to be vague as I am away from my bot right now and just using cad estimates).

Custom (not of the shelf) would work as well its just a last minute change out prior to my May competition. 
Thanks JC

[lo_0l]

@JohnC, 9,000lbs is quite a bit of pressure. You're definitely headed towards needing engineering support unless you can find or adapt something off-the-shelf. If you're willing to do the calculations on your end, Rock West Composites does have a Build Your Own Tube tool. They have a variety of existing mandrel sizes (ID), and the OD is virtually unlimited. You could talk to @John Kimball about this. You could also possibly under size your tube and then bore and polish it out to your required dimension and tolerance. You could also bore it out, apply a coating to the ID, and then bore and polish it to size.

Is there a particular reason this needs to be made from composite? Are there weight limitations? It seems like aluminum or steel might be a better fit.