My team was considering using some 2" bore 36" stroke length pistons for the wall scale this year. Would these be legal? I see nothing in the manual regarding max stroke/bore length, nor can I find anything more recent than 2005.
Thanks so much!
Legal? Yes. But, legal does not mean a good idea or practical. While large pistons may seem like a good idea, I’d recommend calculating the amount of air needed to actually use them.
Of course. I just wanted to make sure there wasn’t an issue with using them. 
According to the 2015 pneumatics manual, at 60 psi something of this size could lift 170 lbs. The volume needed would be ~113.1 in^3, or 1853.4 ml. This would mean we’d need four air tanks to fill one piston. Doesn’t seem /too/ terrible. It’s definitely doable.
First:
“It’s a cylinder, not a piston”
Brought to you by the IACNAP campaign.
Secondly, if you are pulling the rod back into the cylinder to lift, the area of the piston (yes that’s correct) is reduced by the area of the rod.
Get single acting pistons if you can, otherwise you’ll need 8 tanks.
well not necessarily, you could plumb it so one side is at a lower psi right?
Have you found anyone who sells these? I’m sure they have them but remember that it might be the heaviest single part of your robot and will definitely take away from your weight/pneumatic budgets.
Of course there are alternatives. I was assuming the same pressure on both sides because that is the simplest arrangement.
We have one we accidentally bought 4 years ago. https://uploads.tapatalk-cdn.com/20160112/9ebe737620edc014ac0ca2157bfbce12.jpgit’s actually only around 11 pounds.
Here’s one
McMaster-Carr, http://www.mcmaster.com/#6498k485/=10n6o8z
That’s one way to go, we are thinking of almost the same concept, and are preparing to arm many tanks on our bot this year.
Expensive, but it could work, honestly we are looking at putting 2 on the robot stored at an angle. Therefore, roughly half the power per cylinder is needed, but twice the air… the bore wouldn’t need to be a mile wide though, which is a plus.
Sweet Jesus…:ahh:
Yep. Ours is double acting, but we could get away with firing it once using 4 tanks, yes?
Our coach acquired them through the typical BIMBA voucher in our rookie season. He had no idea how large they were and we’ve just had them laying around. I took a look and thought they might be effective for this year.
You could fire only once if you spring loaded the return/lift motion
Makes sense.
you don’t really need to worry about the volume of your tanks as you need to worry about the volume of your pump and the diameter of your tubing.
filling a cylinder like that with 1/4" tube would take forever.
You could use smaller bore cylinders if you added powerful constant force springs (free from Vulcan Spring](http://info.vulcanspring.com/first-robotics-competition)).
For example, if you pre-loaded your lift with 40 or 50 lbs of force then you have to push the springs up when you’re extending, but only have to pull 70-80 lbs when retracting.
Of course you want to design in a fudge factor for safety.
Our Team tested this cylinder with ~120 in^3 of storage capacity lowering and lifting 135lbs. Here’s a video link of the test:
We used the pneumatic system from last years robot to get an idea of the air flow and the load on the compressor.
1518’s video seems to confirm this
Those batteries should be wrapped in electrical tape or heat shrink… those look dangerous
We prototyped this and learned a couple things that I’m happy to pass along.
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Bimba sells double-wall cylinders that go much longer than the standard 24" that the singles do. They weigh slightly more, but since it’s lifting the robot, I would’ve considered putting the cylinder in a tube to protect it anyway. 6.7 lbs for a 36" we bought on ebay.
Here’s a 28" for sale on ebay today.
http://www.ebay.com/itm/BIMBA-DWC-6028-2-DOUBLE-WALL-PNEUMATIC-CYLINDER-2-1-2-BORE-X-28-STROKE-/151469157440?hash=item234443ec40:g:X30AAOSwrx5UXm0g -
a 2-inch cylinder on pull (subtract out the shaft area) can lift about 170lbs at 60 psi. Don’t forget that your 120 lb robot has a battery and bumpers. Also, the friction of the bumpers dragging against the tower will be significant, based on your bumper design and the placement of the lift-point on the robot. We lifted a very heavy older robot (150lbs?), but we had to go to 65 psi to actually climb the wall with a 2-inch cylinder. Not doable there.
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Yes, we had two black tanks and they emptied in the first six inches. But the overall lift powered by a Thomas compressor still finished in the 20 seconds. More like 15 seconds.