"hydraulics"

Anyone else have the problem of people coming in to look at the robot, then shouting out "Hey, look at the cool hydraulics!" WE have to constantly tell people that they are pneumatics, not hydraulics.

[JoshJ]

Lol yeah, that just happened to us at one of our meetings. The little brother of our pneumatics guy sat and argued with him about whether or not they were pneumatics or hydraulics.

[Sscamatt]

most people don't know the difference between pneumatics and hydrolics...i didn't know until a few years ago

[Aignam]

Yeah, when we practice with the robot in the commons (our school's main passing/social area) we'll get a number of kids with the usual questions/comments.

"Cool! Hydraulics!"
"What does it do?"
"Can I drive?"
"WOW! A battlebot!"

[ngreen]

Or the sarcastic one:

"It doesn't fly"

You can let them assume it is hydraulics unless they need to know different. Their are only slight differences kind of.

[pras870]

It's easy to get mistaken, the only difference between the 2 is that hydraulics is powered by a fluid of some time (water or sometimes an oil of some sort) while pneumatics is powered by air.

[IndyStef]

Originally Posted by pras870

It's easy to get mistaken, the only difference between the 2 is that hydraulics is powered by a fluid of some time (water or sometimes an oil of some sort) while pneumatics is powered by air.

BIG difference!
Air is compressable, hydraulic fluids are not (usually oil, rarely water)! That means that pneumatic systems can store energy relatively easily in a tank, but are not very accurately positionable under changing loads. Hydraulic systems are a lot heavier, and all energy has to be provided by the pump at the time when its needed (unless a pneumatic tank stores energy - in which case you could use pneumatics right away).
For the uneducated admirer of the bot, though, they are just the same LOL

[kmcclary]

Originally Posted by IndyStef

BIG difference!
Air is compressible, hydraulic fluids are not (usually oil, rarely water)! That means that pneumatic systems can store energy relatively easily in a tank, but are not very accurately positionable under changing loads. Hydraulic systems are a lot heavier, and all energy has to be provided by the pump at the time when its needed (unless a pneumatic tank stores energy - in which case you could use pneumatics right away).

Yes, the most cited air/hydro differences are: compressibility (vs non), and a MUCH higher average working pressure in hydraulic systems.

But it is not true that a hydraulic system HAS to be limited by the pump's output. There are devices commonly known as "hydraulic accumulators" or "hydraulic surge suppressors". (You can web search on them.) These devices DO accumulate energy for hydraulic systems in the same way that the air tanks accumulate energy for pneumatic systems.

The main parts of a hydraulic accumulator are an expandable chamber for the fluid, working against a "spring force" of some kind. This is often implemented as a very high pressure vessel with a flexible diaphragm of some kind bisecting it and air on the other side to act as the spring, or as a hydraulic piston with a VERY heavy duty spring, air, or displaced vertical weight giving the back force.

For example: Smart multi-car hydraulic "elevator array" systems in buildings can use the unused elevator cars as "accumulators". They SWAP energy for "nearly free rides" with valves by sending one or more empty cars one way as the full one goes the other, or transferring the surplus "down" energy into a BIG standard accumulator to be reclaimed later for "up" use. Down can ALWAYS be had at any time by simply opening a valve. A Smart Array system (hydraulic OR electric based) can save the building owners a LOT in energy costs over the long haul.

Anyway... Standard compact hydraulic accumulators are NORMALLY used for one of these reasons (there may be others, but these are the most common):
A) To store energy for high frequency actuation you otherwise couldn't directly GET out of a pump;
B) Act as a "shock absorber" to help reduce "water hammer" effects, or
C) Allow a MUCH smaller "average capacity" pump to be used instead of a large "peak" one, for serious cost savings.

Just like with air, once an accumulator is pumped up, you can go crazy for a while with the actuators. However, pressures in a HYDRAULIC accumulator vessel can often exceed several THOUSAND PSI. The volume depends on your application.

The total energy stored is related to the total displacement volume times the maximum rated working pressure. IOW, a HECK of a lot of stored hydraulic energy can be had in just a TINY accumulator package, as much as a HUNDRED times higher than is available in OUR air based systems of the same size. "A couple thousand PSI" systems are fairly common. Anything over "a few thousand PSI" hydraulic systems DO exist, but are VERY dangerous, and take special plumbing parts and rules to avoid ruptures.

For safety, systems with hydraulic accumulators MUST include a way to CAREFULLY purge the energy stored in them. The easiest schematically is to add a simple bleeder/purge valve between the high pressure side and the oil reservoir.

BTW, hydraulic systems can be much more complex, too. Some components (like decent servo valves) may require microscopic oil filtering to eliminate even tiny contaminants for proper operation. I've once been in situation where even cracking a system for a SIMPLE change may lead to a DAY of lost time refiltering the entire oil load. But that's an extreme case...

I worked with accumulated systems when I helped a well known auto company develop their hydraulic active suspension system. Trust me, you quickly develop a HEALTHY respect for the kind of stored energy that can make a multi-ton car make significant corrective motions several hundred times a second, using only a hydraulic pump similar in size to our FIRST air pump, and a hydraulic accumulator not much bigger than a large grapefruit! Your health and safety hinges on proper procedures and rituals, and you think TWICE before taking ANY action in the lab.

During R&D tests, we even once had a full sized car jump over a foot straight up into the air on powerup due to a software error. (Whoops...) You might say, "there were puddles everywhere"... Trust me though, not ONE of them was the car's hydraulic fluid!

...And THAT is why we don't include even NON-accumulated hydraulics in FIRST contests, and seriously limit working pressures! If you think an air piston can be dangerous, imagine a TINY hydraulic system which can EASILY produce THOUSANDS of pounds of crushing force in a gripper using with an itty bitty cylinder. In addition, hydraulic oil spray from a leaky high pressure connection intersecting a person can "pressure inject" oil directly under or even THROUGH your skin. NOT fun, and it may require some messy surgery to attempt to clean it out. (I've seen it happen... Luckily, it was an arm and not a FACE...)

But ACCUMULATED hydraulics are WORSE. They're that dangerous WELL AFTER the power is cut off. One mistake with a well sealed but unpurged multi-K PSI accumulator based system (even DAYS later) could easily be crippling, or fatal. On the suspension project, we had some SERIOUS safety classes before we could even get NEAR the project hardware.

Now, I don't mean to scare anyone off from the field. Accumulated Hydraulic systems are VERY USEFUL, and some things simply can't be easily done WITHOUT them. But they're VERY serious systems, not something to "play with" as a first time user. Air is MUCH better for learning on, and teaches you the same things with fewer safety issues. NEXT comes Basic Hydraulics, and THEN Accumulated and "High Pressure" Hydraulics.

I'm SURE we'll be sticking with low pressure, "limited storage" air for THIS contest. I just want people to know that the field of "Accumulated Hydraulics" EXISTS, and can be quite exciting!

(I hope this has been informative...)

- Keith

[Elgin Clock]

Originally Posted by Aignam

Yeah, when we practice with the robot in the commons (our school's main passing/social area) we'll get a number of kids with the usual questions/comments.

"Cool! Hydraulics!"
"What does it do?"
"Can I drive?"
"WOW! A battlebot!"

That last one got old REAL FAST!!!

[Paradox1350]

Originally Posted by Sscamatt

most people don't know the difference between pneumatics and hydrolics...i didn't know until a few years ago

I didn't know until February 19 at 5 PM when my team decided that we would be using pneumatics and I had to learn how to hook them up right and make sure it was programmed correctly . . .

Oddly enough the penumatics worked perfectly on the first try.

It seems that, in FIRST, the harder something is to do, the more likely it is that you will get it to work. We've done at least 4 good things completely by accident.

[Tom Bottiglieri]

as a janitor who walked into our room said.. "What are you STUPID?! That things never gonna fly!"

Then..."What is this, Monster garage?"

*Stephen shows the janitor our arm mounts, telling him they are the 50 cal cannon mounts...*

"50 Caliber, now thats what I'm talking about!"

[greencactus3]

fill 4 tanks to 120 psi. release all the air into an aluminum tube with inside diameter of 3/8..... ther is a steel 3/8 rod inside.....
goes through a couple pizza boxes and quite a bit more.....
now WHO says hydraulics are more fun than pneumatics???

EDIT: make sure you have your safety goggles on!!!

[KenWittlief]

pneumatics are more fun to play with because hydralics are so slow

you cant compress hydralic oil so you have to pump it to make the cylinders move - the speed of the cylinder is dependant of the speed of the oil through the pump.

but with pneumatics, you can pressurize a tank and BLAST it into the cylinder in a fraction of a second

(or so I have been told :c)

[russell]

We are built our bot in a "special education" classroom. About four people every day would ask us if it could go off jumps or grind railings and just generally stupid questions.

[pryoplasm]

Originally Posted by greencactus3

fill 4 tanks to 120 psi. release all the air into an aluminum tube with inside diameter of 3/8..... ther is a steel 3/8 rod inside.....
goes through a couple pizza boxes and quite a bit more.....
now WHO says hydraulics are more fun than pneumatics???

EDIT: make sure you have your safety goggles on!!!

we might have done something similar with a single tank, 100 psi and launching a drywall screw through a piece of 1/4" plywood....also rigged it to a air horn for some ear drumming good fun, we almost defeaned, well half the team at 100 psi....hearing protection for the people running the horn a must, after the first try my ears were ringing for the rest of the day...