Reversing the compressor is a bad idea. Especially when we have a venturi vacuum generator that works perfectly fine with compressed air. Plus the advantages of using the compressor are that multiple functions can be powered by the compressed air it generates.
There are other, non-pneumatic, ways of producing a vacuum. Driving a piston with a motor works, but relies on a good seal (you can only evacuate the length of the piston). Drawing a good seal is still important for continous vacuum device, such as the venturi or a KOP motor+impeller, but since these type are always drawing in air, loss of seal doesn’t mean loss of object.
One other disadvantage (or advantage) of piston type suction devices are that once the seal is made, the amount of suction is determined by how far the piston rod moves. Since continous type are open to atmospheric pressure the vacuum is determined by other things like air flow rate and pressure or motor speed.
If you are using pneumatics this year, the venturi pump is great. If you not going with a pnuematics a KOP motor with an impeller (FP with an impeller from a small shop vaccum worked great in '04) will work and can fairly small and light (you only near the small motor, impeller (plastic), and a housing).
They (the copresssors) make the same air pressure when wired backwards, (don’t argue), the problem is the cooling fan runs the wrong way and the compressor will overheat early.
I can think of being able to evacuate with a partial throw and continue to slightly move the piston as one way.
Another way is when the end of the stroke is reached, switch the vacuum side of the piston to atmospheric pressure (solenoid with other outlet blocked) and move piston to starting position, swithc to open to the suction device again and then continue to evacuate.
Or the third is to run two connected pistons driven by a crank shaft with switching between the two vacuum chambers via solenoid.
The third is the most complex and closest to a continous vacuum. The second you have to stop for a bit to move and the first you still are stuck at the end of the throw.
edit: actually a single piston would work for the third. Just use a solenoid to switch because either way you pull/push the piston you will get a vacuum. Still this isn’t continous because of the stops at the ends of motion. Also without care the switching may introduce enough atmospheric air to break the seal.
I forgot to mention the obvious for this earlier the compressor uses check valves in the head so even if you run the motor backwards its still a positive displacement pump.
So, vaccums don’t count as pnematics. That leads me to two questions. One, if you run pneumatic devices with a vaccum, will they just work in reverse?
Second, if they work, does that mean we can forgo the pneumatc rules and use whatever actuators we want?
Is there an image/scematic for the most basic vacuum system using solenoids and the air storage tanks?? can you please post a url to it or maybe email it to me?
Wait a sec… That won’t work. There’s simply no way to run the kit Vacuum Generator (VG) an entire round solely from tanked air.
Unless you are generating vacuum with a kit motor and a pump assembly, you’ll need the compressor, just to operate the VG. The kit VG is a Venturi device. Think of a soda straw that you blow across, to raise the liquid in a drink cup. It works like that. So, the VG is going to require constant airflow running through it just to operate, whether or not you’re holding ANYTHING. Without a compressor, you’d run out of tanked air in only a few seconds after the very first time you activated your vacuum generator!
The basic schematic for a compressor based system is shown in the 2007 Pneumatics Manual. (See the sticky link for it at the top of the Pneumatics Forum.)
That said… IF you can come up with a vacuum pump assembly that you can hack to be run by a kit motor, NOW you have something! Your simplest move would be to design a “reversable air pump”, and directly connect it to your suction cup. Run it one way to stick, and reverse the motor to blow-off the ringer.
If that’s not possible, you’ll need to either vent the line between your motor based homebrew VG & suction cup with a valve of some kind (the kit valves won’t work for this app - they require pilot air pressure to work at all), or else inject compressed air with a separate valve into the line. (The latter IS possible with kit valves, but the system is more complex than a venting solution, since you’re right back to requiring stored air or a compressor, JUST to run the kit valves!)
Kit motors and scrounged shop vac parts or serch for two stage vacume motors from surplus places. Remove motor guts, attach pulley, belt and kit motor, gear for between 15k and 28k (hope to keep current under 46 amps). Built two models last year. Never used them in competion.
Biff
compressors are heavy and fittings are heavy
are you shure you are making the most wheight efficent decision?
wheight of part vs eficenty
a griper can be just as efficent
Has anyone else found that the suction cups really suck?
all puns aside… our team experimented alot with them and found that they were far from perfect, not only do they add a lot of weight, they take time to connect to the tubes [for the suction to build up] and are fairly easily knocked off the robot.
im thinking of trying the piston method as suggested above, since thats weight efficient and would probably be fairly powerful.
but i think custom suction cups are the way to go
The rules state that you absolutely never can and/or should reverse polarity on the compressor. If you do that the FIRST Safety Nazis will make you change it. Just use the vacuum pumps in the Kit (you can order more w/ cups for about 30$ from PIAB.com)
To add to that, OTHERS have already stated (I’m not trying it to verify!): IF you try reversing the compressor, due to the valving inside it is still a compressor! The thing you lose is COOLING. The fan is not blowing air properly across the fins anymore. The compressor overheats, and given enough time it potentially become damaged, or destroyed.
So again, do NOT try reversing the compressor!
(I’m not sure about that one team’s claim of being able to use the compressor as a vacuum pump. I’m curious how they actually did that.)
Keith McClary
Chief Engineer, Team 1502, “Technical Difficulties”
Your simplest move would be to design a “reversable air pump”, and directly connect it to your suction cup. Run it one way to stick, and reverse the motor to blow-off the ringer.
How do you connect the vacumm to the pnuematic parts and pump.???