Is there a valve that will allow the cylinder to stop at any point of the stroke? Or should this all be done in programming?
Andrea Hudson
The Bimba pistons can be obtained with a magnetic sensor to allow for this.
It’s usually not something you’d ask pneumatic cylinders to do, however. The sensor will tell you when the piston passes a certain point in its travels but it’s unlikely you’d be able to come up with an active system to KEEP it there. Since air is compressable, most people think of pneumatic cylinders as binary devices, they are either extended or they aren’t.
Good point Dale … I misread the OP and missed the “stop” portion. Thanks for the clarification.
It is difficult to stop a cylinder in mid-stroke. It can be done but I wouldn’t recommend it to a FIRST team.
If you want to have multiple positions it is best to use multiple cylinders.
Agreed, I would use multiple pistons. That shouldn’t be an issue this year because of the unlimited number of air tanks.
We’ve done this once. On our 2005 robot Sidewinder on our arm. We used a special valve. A 3 position, center closed valve. Something like an SY3340 SMC Valve.
http://www.smcusa.com/sections/first/SY3000valves.pdf
When you energize the coil on the valve the valve will extend the air cylinder, when you take away the power from the valve, the air cylinder with stop in mid-position. It’s not going to be ACCURATE by no means, but it does allow for mid-stroke air cylinders. Of course if you energize the retract side of the valve, it starts to retract the air cylinder and will stop on the way down too.
You can also do it with 2 valves. Use one for direction, the other to open/close the exhaust from the ‘direction’ valve. We used this with our ‘tetra’ arm, worked well.
Here is an example of how to plumb it: http://www.chiefdelphi.com/forums/showpost.php?p=671701&postcount=5
And a whitepaper: http://www.chiefdelphi.com/media/papers/1476
Except for this:
<R74> Each commanded motion of a pneumatic cylinder or rotary actuator must be accomplished via the flow of compressed air through only one approved pneumatic valve. Plumbing the outputs from multiple valves together into the same input on a pneumatic cylinder is prohibited.
it looks like they dont want double imput. well that that would be connected to the output, so it would be legal?
They do make multi-stroke cylinders as well, which are accurate AND simple.
http://www.bimba.com/pdf/catalogs/FL_OriginalLine.pdf
Go to page 67 for the three position cylinders, I’m sure you could find cylinders with more positions from other suppliers if you looked hard enough.
Hey everyone, I know this has more than likely been already covered but our team has read the rules and read the rules but we still cannot find exactly how many canisters, (Used for Volume) we are allowed to use?? Can anyone help? Please? Thank You!
There is no limit as to how many pneumatic storage tanks you can use this year.
From the FRC Forums:
Team Update #2 makes doesn’t give a limit to the number of pneumatic storage tanks a team can use. This makes it sound like teams can use an unlimited number of storage tanks on the hostbot. Is this true?
GDC: Correct, there is no explicit limit on volume of stored air permitted on the ROBOT.
hey thanks for the reply! thats exactly what our team thinks about it! but we’re not exactly for sure ya know?