Spring loaded Pneumatic piston

[Peter Matteson]

Traditionally we have not been allowed to use them but I have to say I don't see any rule against it this year.

Normally the GDC's round about way to get prevent use of spring return pistons is that you can only use cylinders equivalent to the free order form parts from Bimba which did not include spring return, bore size and stroke. This year <R73 D> only has a maximum bore and stroke.

I'm actually surprised they opened it up this way finally.

Edit: I guarentee that it is asked at least 6 times in the official Q&A anyway because this question is asked every year.

[IndySam]

Originally Posted by Peter Matteson

Traditionally we have not been allowed to use them but I have to say I don't see any rule against it this year.

Normally the GDC's round about way to get prevent use of spring return pistons is that you can only use cylinders equivalent to the free order form parts from Bimba which did not include spring return, bore size and stroke. This year <R73 D> only has a maximum bore and stroke.

I'm actually surprised they opened it up this way finally.

Edit: I guarentee that it is asked at least 6 times in the official Q&A anyway because this question is asked every year.

They opened it up last year. Teams did use spring return cylinders. Please don't call them pistons.

The problem with spring return cylinders is you are stuck at the return rate the manufacturer gives you (unless you find someone who will make custom ones.). It's not hard to use a little surgical tubing and make your own spring return where you decide how much spring to use.

[Al Skierkiewicz]

If you are talking gas shocks then those were allowed last year. If you are talking a spring inside a pneumatic piston that is connected to the pneumatics system that is another thing. I do not remember that something like that was allowed last year. From this year's rules
R72
I. For the purposes of the FIRST competition, closed-loop pneumatic (gas) shocks are not considered pneumatic devices, and are not subject to the pneumatic rules (although they must still satisfy all other appropriate rules).

[Team2191]

No not the gas shocks. A pneumatic cylinder with a spring bias forward or backward.

[Al Skierkiewicz]

Do you have a part number and supplier?

[Jared Russell]

Al:

McMaster sells spring loaded air cylinders. See: http://www.mcmaster.com/#pneumatic-cylinders/=5dun1p

The single acting, spring-loaded cylinders look to me to meet all of the pneumatic rules this year (assuming the bore and stroke are within the limits in the manual, and the cylinder is rated for sufficient pressure).

In my opinion, the main advantage of these cylinders (besides simplicity and one less air connection) is that you are guaranteed that they will return to a known position in the event of an air loss event. In the case of a two-speed, air-powered, dog-shifted transmission, this means that you will always be in gear even if you lose air pressure.

[Al Skierkiewicz]

Thinking.....
This raises some safety issues. Does anyone have other types they are thinking of using for a larger data sample?

[Jared Russell]

Originally Posted by Al Skierkiewicz

Thinking.....
This raises some safety issues. Does anyone have other types they are thinking of using for a larger data sample?

Al,

Could you elaborate on what safety issues you foresee with spring loaded cylinders of the type I posted? If anything, I could see them being safer than traditional double acting cylinders. (In extension, the total force is reduced by the amount of spring force; in contraction, only the spring is providing force).

[Al Skierkiewicz]

Jared,
Although there are no rules that prevent operation without power, I have never liked robots to move when the system is vented. If these types of cylinders are used, some part of the robot can move when the valve is opened.

A personal wish for safety.

[Tristan Lall]

As of last season, the pneumatic cylinder rules were greatly relaxed—the best robot rule change in a while—and seem to pretty clearly permit all sorts of strange and wonderful cylinders. (Your stroke, diameter and pressure rating are still restricted.)

Since the GDC didn't say (in this year's or last year's rules) that single-action cylinders were distinct from double-action models, I don't think there's any issue with using the manufacturer's definition of a cylinder (which happens to be accepted in industrial practice). I therefore don't think there's any point in asking this one on the Q&A.

Of course, the robot must still satisfy safety rules with regard to energy storage, and the spring in a single-action cylinder will be inspected as such. That shouldn't be a major obstacle, however—lots of teams use springs.

[Al Skierkiewicz]

Originally Posted by Tristan Lall

Of course, the robot must still satisfy safety rules with regard to energy storage, and the spring in a single-action cylinder will be inspected as such. That shouldn't be a major obstacle, however—lots of teams use springs.

Tristan,
I was thinking along the same lines but this does need a little more research.

For those reading this thread, I know stored energy is going to a big concern during inspections. Springs, surgical tubing and pneumatics are all going to be used to direct the ball. Safety in the use of these devices is going to be of prime importance. Be sure you have the ability to release energy before leaving the field as in previous years and follow this...

<R01> Energy used by FRC ROBOTS, (i.e., stored at the start of a MATCH), shall come only from the following sources:
A. Electrical energy derived from the onboard 12V battery (see Rule <R40> for specifications and further details).
B. Compressed air stored in the pneumatic system, stored at a maximum pressure of 120 PSI in no more than four Clippard Instruments tanks. Extraneous lengths of pneumatic tubing shall not be used to increase the storage capacity of the air storage system.
C. A change in the altitude of the ROBOT center of gravity.
D. Storage achieved by deformation of ROBOT parts.

Teams must be very careful when incorporating springs or other items to store energy on their ROBOT by means of part or material deformation. A ROBOT may be rejected at inspection if, in the judgment of the inspector, such items are unsafe

[JesseK]

Originally Posted by Al Skierkiewicz

Jared,
Although there are no rules that prevent operation without power, I have never liked robots to move when the system is vented. If these types of cylinders are used, some part of the robot can move when the valve is opened.

A personal wish for safety.

It's about the same effect as a robot with a single solenoid valve when the robot turns off.

[BJT]

the spring in these cylinders is usually very light. I was looking at a 1.5 inch bore single acting spring return cylinder and the specs said the spring had only about 6 pounds of force. I think the spring is always used to return a single acting cylinder, not to assist its push.

[Team2191]

Originally Posted by BJT

the spring in these cylinders is usually very light. I was looking at a 1.5 inch bore single acting spring return cylinder and the specs said the spring had only about 6 pounds of force. I think the spring is always used to return a single acting cylinder, not to assist its push.

if we were to use a spring loaded cylinder we would use the 2" bore with a 4" stroke and a front spring bias. this accomplishes the extra force needed and the extra velocity. the spring described in this system has 30 lbs. force by itself. with the pneumatics added this will be increased more. btw this is offered by clippard