Not enough info.
One issue re pneumatics is safety.
Having a metal arm being moved by pneumatics can be dangerous. I think most if metal are done in aluminum, not steel. This is to save weight and reduce mass which equals danger. You could go the PVC route. No welding required. Plus lighter and perhaps a bit less dangerous.
Please provide a detailed description of what you want to do.
You may want to search for other pneumatic prop examples.
One issue re pneumatics is safety.
Having a metal arm being moved by pneumatics can be dangerous. I think most if metal are done in aluminum, not steel. This is to save weight and reduce mass which equals danger. You could go the PVC route. No welding required. Plus lighter and perhaps a bit less dangerous.
Please provide a detailed description of what you want to do.
You may want to search for other pneumatic prop examples.