Pros and Cons of Using Pneumatics

[Joe_Widen]

What are the pros and cons of pneumatics. How does your team justify the use of all that weight for say only a two speed shifter. or one mechanism. Also, how do you find the weight to put the pneumatics system in there. My team tried it our first year, and we didnt have the weight. (25 ounds over) I've always like pneumatics because I havent seen them fail really. Why are pneumatics better than leadscrews. I guess its a bit scrambled but I guess the only way to justify them is by using alot of them. What does your team determine as alot?

[sanddrag]

For the past two years we have used pneumatics only for shifting. We use only one air tank and the smallest possible cylinders and no compressor so we get by. We design most of the other stuff to be pretty light (small wheels, sprockets, and chain, aluminum axles, and so on).

[anna~marie]

Our team usually tries to work without pneumatics, if there is a better way. We've had problems in the past with them and find the hassle not worth it if there's a better alternative. The past two years of HOT robots have no had pneumatics.

[EricH]

Cons: Weight: There aren't a lot of things heavier than the compressor in the kit, and the tanks weigh a bit too.
Limited use: You can only use them for a few things. the last time we used pneumatics, we had: 2 gear shifters, a winch lock (to keep us on the bar in '04), a wheelie bar deployer (to keep us from tipping), and an arm extender that didn't work too well against gravity.
Battery drain: If you use them a lot, the compressor will reduce your battery power as it runs.

Pros: Simple: one shot power for just hooking it up right, and a minimun of programming.
Won't stop when power turns off: useful if you need to climb on a bar or retract something at the very end.
Hard to backdrive: won't reverse without instruction, as long as the tanks are full.

As a side note, use of pneumatics is a lot better than it was back in the day. Many years ago, you got one huge tank (13 lbs or so, 10% of your weight budget) that would store all your air for the whole match and one cylinder that was your entire system (and often was the wrong size). Now it's a compressor, storage tanks, and your choice of cylinders.

[Donut]

Our team has used pneumatics (with an on-board compressor) in 5 of our 6 robots, with this year being the first year we didn't use them. It actually took alot of convincing and arguing with the lead mentor to convince him we could get by without them this year and needed the weight save.

Pros have to be their ease of linear movement, the amount of power you can get from them, and their relatively low failure rate (we have never blown a fuse in competition, though for some reason they enjoy frying during demonstrations in the off-season). The ability to lock them in a final position and the difficulty in back-driving them are good as well. And although the compressor is heavy, the actual cylinders are relatively light and work well on long arm extensions that can't afford a large motor.

Cons are weight, space consumption (for the compressor and storage tanks), weight, limited quick use (if you repeatedly use them quickly you must wait a few seconds to get some air pressure back), and weight.

In all honesty we probably would have used them again this year if the compressor wasn't so heavy (and we're firm anti-believers of the idea of not having an on-board compressor for pneumatics). In 2005 we used a cylinder as the final extension on our arm (we didn't want a motor 11 feet in the air) and used two for a tetra holder that ended up being worthless and unused. In 2004 we used a cylinder for a ball claw and 2 cylinders for herders on each side of our robot. 2003 had an identical setup with the cylinders used for grabbing bins instead. 2002 used a cylinder to grab the mobile goals, a cylinder to raise our ball holder up above the goals, and a cylinder to release the balls into the goal. 2001 had some as well but I don't really remember that bot.

[KenWittlief]

Personally I think the pneumatics system is one of the greatest things in the KOP.

You need to approach it from a robot-system perspective. The cylinders can be very small and very light in just the right place (at the end of an arm for example), while the heavy compressor can be low in the center of your robot to keep your center of gravity close to the floor.

You can get cylinders that will extend 2 feet in less than a second, with a considerable amount of force, and weight less than 8 oz. You cant do that with a lead screw.

If your team has not been able to get pneumatics to work, then you need to figure out why in the off season. The system is fairly simple to use, and as long as you have no air leaks it should be very reliable.

There are a few tricks you need to know, for example, when you attach the tubing to the fittings you push it in, then pull back on it to get it to seat securely (otherwise it will leak).

Also, dont mix tubing or fittings from previous years. Over the years there have been a couple different sizes of tubing used.

[Not2B]

Here's a big ol' PRO:

Because the team gets to learn about and use something they might not normally be exposed to. This is my big arguement for pneumatics.

This year the engineering design process did not allow us to use pneumatics, as being exposed to (and following) a design process is also important.

SO... our summer T-Shirt (And Parade Candy) Launcher is under contruction!! Sadly, it uses only limited pneumatics.

[Stephen Kowski]

I think that the KOP is great, but I cannot seem to get over how much it weighs. If you need a linear actuation it is going to be hard to get a better effectiveness through a rack and pinion, lead screw, or something else but the compressor and the tanks are a needed evil to do this. My main issue is that you have no choice with the pnuematics even though there have been hints over the years we may see some changes. We don't ever have more than two cylinders nor can we change the compressor to something smaller/lighter.

I know where pnuematics are the best option, but adding the entire circuit for one function is not worth it. There have been upgraded motor, controllers, electronics, lights/blinking LEDs, when will we see some changes to the pnuematic circuit beyond how many/what kind of solenoids we can use (I believe that was 2004 when it was under direst because of the lack of stock from SMC)?

[Jeff Waegelin]

When discussing the "weight issue" of pneumatics, I like to use an analogy to economics: pneumatics have high fixed costs, with low marginal cost, while motors have high marginal cost but low fixed cost. In this case, "cost" can represent weight and complexity of design. When you add pneumatics to a robot, there are a lot of support pieces you need (compressor, tanks, etc.) that weigh quite a bit. However, each individual cylinder represents only a small increase in both weight and complexity of your pneumatic system. Thus, the "cost" of adding pneumatics to a robot is high, but once you've added one, the "cost" of a second is pretty low.

Motors, on the other hand, don't really require any additional fixed weight, as everything they need (battery, RC, breaker panel, etc.) is a required component of any robot. Adding each one, though, can add lots of weight for the motor and any associated gear reduction. So, unlike pneumatics, there is no real fixed startup "cost", but each additional motor can be a major increase in "cost".

My philosophy in using pneumatics in FIRST is based partly on this idea. If I use pneumatics, I generally prefer to use them for as many functions as possible. Once I've added a compressor and all the other support pieces, it's easy to add more, and can be a very weight-efficient plan. On the other hand, if I only have one use for pneumatics on a robot, I will generally try and eliminate that mechanism, or change it to a lead screw or other motor-driven mechanism, so as not to have to add all the weight associated with that initial pneumatic cylinder.

All things considered, I like pneumatics. They're fairly easy to work with, fast, reliable, and consistent. Lightweight manipulation on the end of an arm is also a great feature. But, if I had no pneumatics on my robot, and a choice between adding 5 lbs. for a small motor and lead screw, or 15 for all the pneumatic equipment... it's an easy choice.

[Lil' Lavery]

Sense 2003 (my first year on 116), 116 has used pnuematics on 3/4 robots, this year being the only we didn't.
In 2003, we used pnuematics for shifting only.
In 2004, we used pnuematics for shifting, and our herding arms (later replaced by a pnuematic wheelie bar).
In 2005, we used pnuematics to extend a moment arm to make our winch expend less power to raise our arm (and later we added a pnuematic "claw" to keep tetras from falling off of our arm).
We had an on-board compressor for all 3 years.

Pnuematics are a tremendous asset for your robot, and are terrific for linear motion. They are quick, simple, and reliable, much more so than motors. While the compressor and air tanks may weigh a fair bit, you can position them near the base of your robot, therefore improving your CG and stability. The actually pistons are typically very lightweight, and won't hamper your total weight budget or center of gravity much. Motors can be quite weight, especially when you factor in gears, chains, pullies, and other mechanisms to adjust the motors speed and moving the force to other locations.
Motors have a greater degree of control though. In FIRST applications, pistons can either be extended or retracted, while motors can be anywhere in between.

I prefer to use pistons wherever you do not need huge degrees of control, as they are, in total, often lighter components than motors, and typically much simpler to design and constuct, recquire less space, help lower CG (usually), and are quicker at accomplishing functions.

[DonRotolo]

Pros: Can be fast, can be powerful, very repeatable positioning, air is a good energy distribution medium, reliable, simple, levers can be used to trade distance for force.

Cons: Air compresses, so the cylinder can't hold a varying load without movement. Difficult to have positions other than the end points. Compressor is heavy and power-hungry.

Plus everything said above.

Fon

[Daniel Morse]

During my time on my team, we have had two robots with pneumatics ('03,'04) and two without (05',06'). It is pretty much the same problems that get us every year, weight and performance of the compressor (too weak). In the past we have had very intensive, repetitive operations to be performed by pneumatics, and we have to wait for them to recharge (only one compressor, and many jobs) in order to complete an operation, which, as you know, is a huge liability. Also, we often cannot afford the weight, the performance is simply not high enough to justify us using it. On the pro side, the pneumatics give us a way to apply constant force without having to have a motor bias to maintain it, and are a great way to bring something to the same position over and over again. Speed is also a plus. The last two years we have used no pneumatics, and it has worked out for us in a positive way. 3 and 4 years ago, we used pneumatics and really, I don't think anyone has any regrets. When it comes down to it, after four years with seeing the results of both using and not using pneumatics, it seems to really depend on what you are trying to accomplish and what demands are to be placed on the system. After looking at these factors, you can make an informed decision as to what you need.

[=Martin=Taylor=]

Originally Posted by sanddrag

We use only one air tank and the smallest possible cylinders and no compressor so we get by.

This is what we did this year. And boy oh boy was it annoying.

Oh, sure the mechanism worked fine. I had no trouble with how it all worked. But the FIRST rules regarding off-board compressors were ridiculous.

At our first regional we got into trouble with the inspectors, who made us install a fan and a spike to the off-board compressor.

What controlled that spike you ask? Why the robot of course. We had to lug our compressor out on the field, turn on the robot, hook the compressor to the robot, charge our tanks, unhook the compressor. It was ridiculous.

I don't know if anyone else experienced this. Or if there is some totally logical reason for doing it that I am missing. But I felt this rule to be a little silly.

[KenWittlief]

Originally Posted by Hachiban VIII

... the inspectors made us install a fan and a spike to the off-board compressor.

...Or if there is some totally logical reason for doing it that I am missing. But I felt this rule to be a little silly.

I can think of reasons:

teams jumpering the compressor directly to a spare jell cell, getting the wires crosses and starting an electrical fire (no fuses)

someone getting the idea that 24V on the compressor will fill the tank twice as fast?

Someone who has never used the compressor before, thinking it runs on 120VAC?

if you dont spell out the correct way to power the compressor for off-robot use, then people are left to their own imaginations.

[Richard Wallace]

Originally Posted by Hachiban VIII

This is what we did this year. And boy oh boy was it annoying.

Oh, sure the mechanism worked fine. I had no trouble with how it all worked. But the FIRST rules regarding off-board compressors were ridiculous.

At our first regional we got into trouble with the inspectors, who made us install a fan and a spike to the off-board compressor.

What controlled that spike you ask? Why the robot of course. We had to lug our compressor out on the field, turn on the robot, hook the compressor to the robot, charge our tanks, unhook the compressor. It was ridiculous.

I don't know if anyone else experienced this. Or if there is some totally logical reason for doing it that I am missing. But I felt this rule to be a little silly.

FIRST addressed this in Team Update #18. While the timing of the update could have been much better, its message was consistent with the pneumatics rules that have been in place for some time now. The goal is safety. Basically, you are allowed to save weight by using an off-board compressor, but the pneumatics system must be functionally the same as it would have been with an on-board compressor, and must include all the same components. This has been discussed in an earlier thread.