pneumatics or hydraulics ?

[rexi]

I am trying to figure how to build a chair that would tilt (with a person in it)forward and back and side to side.This chair would be programed by
video game software.My question is ,would pneumatics ,that are used
in robotics be strong enough or is this something that would have to be
hydraulic?

[EricH]

If you don't want to be confined to just two or maybe three points, I'd go with hydraulics. Also, I think hydraulics can give a smoother ride.

[Jay H 237]

As long as you size the cylinder correctly, pnuematics will be plenty strong. The correct cylinder running even 50 - 60 PSI (about 4 millibars) will be enough to lift someone.

The cylinder length will have to be determined by your design. A 1 1/2 to 2" bore should work. The mounting of the pivot points is also critical to how much the cylinder has to work. You will have to do some trial and error here.

[Scott358]

In the end, you'll need to calculate the force you need, then the question can be answered, but as some data, consider the following....

If you use a single 2" dia pneumatic cylinder with a working pressure of 60psi (which is the working limit within FIRST), it will exert 188lbs of force in extension, and 170lbs of force retracting. If you use 90psi (which is more typical in industrial applications), the force increases by 50% (since the force equals the pressure x piston area).

Hope that helps.

[Peter Matteson]

Also remember you can create a jerkier (Is that a word?) motion with pneumatics. Hydraulics would allow you smoother translation.

[Arkorobotics]

Personally I would use electromagnetic actuators. But if it has to be between pneumatics and hydraulics I would choose hydraulics because:
a) really smooth
b) they can be accurate, and extend to a specific distance, rather than pneumatics which is more like point "a" to point "b". there is not a point "a in half". (example: you have a 6" stroke piston, but sometimes you want to extend 4" then like 5" then back to 3" (such as a car bouncing around in the game). A hydraulic can do that very accurately (depending on your equipment))

here is the cons:

a) really messy
b) leaking may happen so make sure you have a "gutterish system" (I really do not know how to prevent leaks, so you might want to search up on that)

Well good luck on the chair, it really sounds like a lot of fun.
Post pictures when you are done, I would really like to see it.

P.S. : http://www.bushleagueracing.com/how_it_works.htm
(this link might give you an idea.)

Motors also can work well (example: the van door motors that come in the KOP)

Good luck ;)

[GeorgeTheEng]

Given that you probably want a lever of repetition and quick response, I would think pneumatics aren't the way to go. Hydraulics are usually a closed system which means no (or much less) recharge time. Unless you want some massive air cylinders. :yikes:

[Jack Jones]

Let me know when you get it perfected. I'll copy and tweak it for use as a WarCraft ejection seat so my son will know when it's bedtime.

[Jizvonius]

Hydraulics are the better choice if you want more precise motion control as you won't have to deal with the high compressibility that gases have. The downside to hydraulics is that you will have to run a pump for every movement as you can't store energy in compression of the fluid as you can with pneumatics.

Both systems can put out the force that you need. You can get the partial stroke movement using pneumatics with the correct valve, but you still don't have precise control of position or velocity.

My vote goes to hydraulics. Just try to find a relatively quiet pump.

[rexi]

Thank you for your help.A lot more help than I expected.This chamber
I want to build will also hold the computer and lcd monitors(2).The chair
won't have to be so strong as to lift a person ,just side to side and
front and back movement.Also would work as flight simulation.

Thanks Rex

[BoyWithCape195]

Heres an interesting prefab motion chair I came across. Maybe it can give you some ideas? Link below...


http://shop.rightthing.nl/index.php?main_page=product_info&products_id=17

[KenWittlief]

Im not sure I understand why people are saying pneumatics are rough, and hydraulics would be smoother?

Pneumatics use air, which will compress. Pneumatic cylinders act like adjustable air shocks, or air springs.

Hydraulics use oil, which is un-compressible. When you extend a hydraulic piston to a certain position it will be rock solid and will have zero give.

With hydraulic valves you can let small rates of fluid through - they are proportional valves, but you can also let large amounts of fluid at high pressure through, and send very violent jerks into the chair someone is sitting in.

[Cuog]

I think that everyone means that it will be smoother(if u want it that way) with hydrolics, with air its very fast and harder to control accurately.

To me it think i would need to know more about the kind of motion you want, it you want it smooth and undeniable but still very flexible(in options) then go pneumatics,

if you want insta-action that is giving but sometimes "mushy" then go pneumatics the choice is ultimately up to you.

[Arkorobotics]

Im not sure I understand why people are saying pneumatics are rough, and hydraulics would be smoother?

Pneumatics use air, which will compress. Pneumatic cylinders act like adjustable air shocks, or air springs.

Hydraulics use oil, which is un-compressible. When you extend a hydraulic piston to a certain position it will be rock solid and will have zero give.

With hydraulic valves you can let small rates of fluid through - they are proportional valves, but you can also let large amounts of fluid at high pressure through, and send very violent jerks into the chair someone is sitting in.

I have seen that before on hydraulic hoists in big OLD auto-shops. Our school use to have an auto-shop before it became the robotics shop, and this had 2 gigantic hydraulic hoists. I remember lifting it without a load on and it would lag and jerk around, but with a load it still did it, just not as much. I think the jerking is due to a lack of oil lubricant. Now I am not sure, but I do agree now, that pneumatics are smoother. I forgot about that hydraulic experience. I know at times pneumatics time to time might have a minor lag, but that is only at low pressures (from my experience). I think mainly because people touch the shaft and leave it out extended and it collects dust.
Thanks for the reminder, I just still say hydraulics because you can regulate the stroke :D . I am not sure if it is the same on pneumatics, because I have never seen a device that can do that.

[rexi]

I have a post puller or frame machine and it uses pneumatics and
hydraulics. the pump is connected to my compressor witch pumps the
fluid into the ram,slow but real strong.

If this chair is to react to video game software ,it needs to be quick
and smooth.Maybe even use an electric motor ,that would pull and
push the chair from side to side,or just push with an opposable spring
of some kind.Braking would be quicker motion forward and a slower
motion coming back to normal position and the reverse of that for
acceleration.Also the chair would have to lean and accelerate at
the same time.Any Ideas I can get get would greatly appreciated.