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Pre-charging pneumatic system
I know the rules state that the pneumatic systems can be recharged prior to the match. However, I am failing to understand how that is possible. The robot only starts the compressor when enabled. When and how do we fill the tanks prior to a match?
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You can directly connect your computer to the cRIO and enable through driver station. At least, thats how we plan to do it.
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You can't do it on the field, but you can do it ahead of time in the pit or in queue.
Spend a lot of effort to make your pneumatic system leak free. |
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Thanks guys, guess I was trying to overcomplicate it!
Mark, we definitely have spent time to ensure our system is as leak free as we can make it. Last time we checked, it took over 2 minutes for it to drop from 115 to 95. Obviously I would like to get it even more sealed than that. |
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We were last at ~6 minutes from 115 to 80 psi. Off to find the crooked tube/bad teflon tape/loose fitting come out-of-bag time!
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Plan for holding pressure a long time.
You don't want to drop any pressure for at least 10 minutes, preferably 30 minutes. A match cycle is 6-8 minutes on average. Some take longer. There are delays when schedules get too far ahead and things have to be slowed down, Head Ref match reviews or hearing of student appeals or corrected scores, robot connection issues, overly long team introductions, being on-field for Opening Ceremonies, or unscheduled VIP drop-ins. The actual match is only 2 min, 10 sec of that cycle time. Add a minute for you to be finished in the queue before carrying the robot onto the field. If having a lot of trouble, then practice making foolproof connections off the robot on a simpler layout where it's easier to identify what's going wrong. Fresh Teflon tape every time a screw fitting is tightened, perfectly square cuts on tubing ends, remove worn tubing ends, identify leaky components (dump valve, regulator, solenoid, pressure gauge, cylinders-extended & retracted), and damaged parts. |
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Add 20-45 minutes if you're told to be on the field for opening ceremonies. Add an hour if it's champs.
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1 PSI per minute is a bit high. 10 PSI per minute is cause for panic!
Make up a weak solution of soapy water and paint it onto each and every fitting. Bubbles will point to the leaks very quickly. |
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Ouch! I didn't realize how bad that is! I will definitely be pushing for curing those leaks during our robot access period. Thanks everyone!
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When I teach a team new to pneumatics, I emphasize that each component should be leak checked extensively before installing it on the robot. I know that this advice is a bit late for your 2014 robot, but it has helped out team immensely over the years. As we typically check each component a week or two prior to installation, final installation is typically a function of hooking up the hoses, and doing a final pressure check.
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One very common place that many teams overlook is the Festo screw in fittings that seem just impossible to make tight from the outside. The trick is to insert the correct size metric allen key into the fitting to allow you tighten the fitting to the body.
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Polytetrafluoroethylene (PTFE) is a synthetic fluoropolymer of tetrafluoroethylene that has numerous applications. The best known brand name of PTFE is Teflon by DuPont Co. |
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It's probably an age thing. I ask for a Kleenex all the time, and I still Xerox stuff for the team. :)
I'll try to be better. |
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A difference which makes no difference ... |
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When in the first match after ceremonies we have always been able to tether on the field and charge our pnuematics. That being said as everyone has already stated, you should make your system as leak free as possible.
I'll stop calling it teflon tape when everyone on CD stops calling cylinders pistons! |
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Thankfully those people don't work in my build space. When I ask for the Teflon tape, I get the white stuff we put on the threads of our pneumatics. It is right next to the Kleenex.
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This thread made me actually laugh out loud, and it hurts to laugh right now as I have a terrible cough.
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Thanks everyone! I now know how to recharge our pneumatic system, so our pistons can be powered. I will be sure to use lots of Teflon! :D :D
I love this thread, thanks for making it awesome guys. |
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Now is it Bar-Loks or zip ties if I wish to bundle some wires??
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Alright, I'll practice using the correct terms.
Next chance I get I'll try asking a student for the polytetrafluoroethylene located next to the facial tissue behind the thermoplastic polycarbonate just to the right of the external-wrenching hexagons under the adjustable end wrenches over by the electrophotography machine. |
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This topic epitomize many of the ChiefDelphi threads out there. Forbid someone write anything not completely correct. I know this thread is in good fun, but I actually know people who wont post on ChiefDelphi because of this phenomenon. :ahh:
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Re: Pre-charging pneumatic system
Jarren,
Since the robot is already together and in the bag (a soap solution will not be the right solution at this time of course)....So start w/ a simple plug or 2. Remove the tubing line running from the completed high pressure side to the low pressure side and insert a plug. (Thereby dividing the system to start searching for leaks in the high pressure half first). Divide & conquer. Power up the robot and let pressure build to compressor shutoff (110 PSI - 120 PSI...Remember, at 125 PSI (the robot inspector will use a jumper on the electrical compressor cutoff or limit switch and bypass/jumper the switch to test this during inspection), the pressure relief valve that is required to be mounted w/ appropriate metal fittings after the compressor check valve, to the actual compressor, should begin to open slightly and bleed off excess pressure to just below 120 PSI...That valve is adjustable...Set it to No Higher than 125 PSI and tighten the jamb nut, but must be done very carefully w/ system under pressure if necessary), and then power off the robot (let sit and record the pressure, and have someone constantly watch the high pressure gauge for any pressure leakdown at all). No leakdown noted...Skip the next step and move on to the low pressure side as you are halfway there already! If, a leakdown though is noted over a 5-10 minute period, listen for leaks, feel for leaks at each fitting or tube end (easier done w/ the robot off and in a nice quiet location without many people around or any other noise generation), release the pressure, fix and repeat. (Quickly check each of those tubing ends for nice straight cuts and proper seating in the fittings too!) Once the high side is fixed (no leaks, & the pressure holds steady for 10 minutes). Then remove the plug and reintroduce the other half of the system (the low pressure side), one item (or circuit), at a time using that same plug and adding items along that low pressure route. These can be accomplished very quickly and the bugs in the system (air leaks), can be worked out without wasting too much robot access or pit time. (You should be able to fix your problem in much less than minutes, to an hour or so done this way, if done very methodically starting at the compressor). A well done system like others have said above will literally hold pressure (if left alone), for days and leak down very little. (IMPORTANT!: Please DO NOT RE-BAG THAT ROBOT w/ any pressure present!) That is a risk that nobody should ever take. During the build we always, after completion of that particular system, mark the robot as charged (Do Not Touch!), and test over time logging pressure checks, and after final practice and robot shakedown & just before bagging, we again check that entire system for any possible leakage present. (Much harder to do in the pits of a very noisy event location). _______________ Now that others here have told you about the pre-charging procedure in advance of placement of the robot on the field, inform those who will be pre-positioning that robot on the field, in the proper handling of that fairly dangerous if mishandled beast please, as it will have much stored energy in it during their placement and can be dangerous to themselves and others if mishandled. The drive team member placing the drivers station on the shelf (and plugging in), also needs some instruction as he holds the actual controls. Then teach them to IMMEDIATELY UPON REACHING THE ROBOT after a match, relieve the air pressure via the dump valve before doing anything else in the retrieval of that same robot from the field after the match is over. ________________ One more suggestion...As soon as you get to your event, seek out a veteran team (Just ask for help...and they will be more than willing to teach you in the name of both safety and professional courtesy)....Then ask lots of questions! Good Luck and be safe! |
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Now to join the others....I'm just a self described dumb Mechanical Type Parent of a Student, FIRSTFRC team mentor (who is still a mentor work in progress myself)...But, the best story I can relate to some of the above "fun answers", was a few years ago now.....I asked a brand new freshman FRC student on kickoff day, as soon as we returned to the team classroom & shop, to please retrieve a pr. of Channel Lock Pliers from a specific drawer of a tool chest...in a specific spot of a specific tray.
He went to that tool chest and stared in the drawer for a good 10 minutes. (I just watched....See, I was a product of the 60's & 70's...Had both wood and metal shop in Jr. High, Auto shop and all kinds of drafting in both Jr. & High Schools (I have worked on machines since being a small child, access to tools was / is my life....So, I sort of impatiently just watched, figuring he'd just figure it out eventually). Many students today do not have many of those electives like we did in school prior to being exposed to the World of FIRST. Back to the story....I sidled over and said very quietly (so not to embarrass him). You have no idea what Chanelocks are, do you? He shook his head no, (still looking in the drawer), and the hurt was quite evident (so we had an hour or so tool lesson right there, in names and what they each allow us to accomplish)... That student who so wanted to learn, had no previous "working on things, or other mechanical type knowledge" whatsoever. But, near the end of just the 6 week build season in his Freshman year, I handed him a printout of a cad drawing "he had just designed," and off he went out to the machine shop. (I sauntered out a few minutes later), and there he was, milling that part to perfection, and our lead Industry Team Mentor, a very patient and filled w/ the love of teaching, a "Master Machinist" w/ over 20yrs. now of FIRST mentoring and dedication (TY to George Williams, your devoted wife, and FRC build season widow & forever FIRST Volunteer Crystal, and your Great Employer & Team 60 Sponsor Laron, Inc.), was not over his shoulder teaching any longer (he didn't have to), but he was watching all of the students as usual from a short distance across the shop. You should have seen the gleam in that students eye, and the pride he had over that perfectly milled part (among many others since). That is the FIRST difference! And that, will keep me coming back long after my own student is gone off to attend college next year, and he hopefully returns to FIRST as an adult mentor (he's been a student mentor already constantly for 4 years now!) Now go grab a kleenex while I reach for some teflon tape...Some of us now have to tend to a leak or 2. |
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