I have a "MTS" system with several cylinders (or linear actuators in MTS lingo). I do general structural fatigue testing of off-road equipment. Normally I run in the 0.5-1.5 cycles/second, but I will probably be getting into low end shaker testing (requirements not known yet, 200Hz?).

My question is, what spool design should I use? Critical/zero overlap? Negative overlap? (I think they have a slight negative overlap.)

The valves that I have bought so far have been directly from MTS, and they don't provide this information as it is "proprietary." The valves are manufactured by Moog, supposedly with special parts for MTS. I can get 76/760/761 series valves cheaper from other sources.

And speaking of spools, one spool option for Moog 760's is a "Pc >80% of Pp". What is this?

Thanks in advance, ISZ

I'm not a Moog guy but, deisgned for applications where pilot supply will see 80% or higher of maximum rated operating pressure?

As far as shakers go, can't help, sorry

quote:

Originally posted by IceStationZebra:
My question is, what spool design should I use? Critical/zero overlap? Negative overlap? (I think they have a slight negative overlap.)

I prefer zero or slightly underlapped.

quote:

The valves that I have bought so far have been directly from MTS, and they don't provide this information as it is "proprietary." The valves are manufactured by Moog, supposedly with special parts for MTS. I can get 76/760/761 series valves cheaper from other sources.

Moog 760/761 are good valves. There are other valves that are just as good.

quote:

And speaking of spools, one spool option for Moog 760's is a "Pc >80% of Pp". What is this?

I have no idea. I have not seen that in the specifications for valves.

BTW, 200Hz is very optimistic, especially if there is any amplitude to the motion.

quote:

Moog 760/761 are good valves. There are other valves that are just as good.

Who else do you recommend? I am limited to a SO4 mounting, unless there are some adapter plates available.

quote:

BTW, 200Hz is very optimistic, especially if there is any amplitude to the motion.

I'm starting to see that. Unfortunatley I don't have any concrete design spec's yet, but my rough estimation gives a displacement <0.005" @ 200Hz. I'm looking at designing a single axis table, about 24" x 24", probably aluminum to help keep weight down. The test specimen is <15lbs. Right now I'm looking at linear bearings vs. a MAST table with only one actuator.

ISZ

quote:

Originally posted by IceStationZebra:

quote:

Moog 760/761 are good valves. There are other valves that are just as good.

Who else do you recommend? I am limited to a SO4 mounting, unless there are some adapter plates available.

That is a problem. I don't now what a S04 valve looks like. I did a search and didn't find much.
I am only familiar with D03 and D05 mountings because we gave them on our test system but I have seen bigger.

quote:

BTW, 200Hz is very optimistic, especially if there is any amplitude to the motion.

I'm starting to see that. Unfortunatley I don't have any concrete design spec's yet, but my rough estimation gives a displacement <0.005" @ 200Hz. I'm looking at designing a single axis table, about 24" x 24", probably aluminum to help keep weight down. The test specimen is <15lbs. Right now I'm looking at linear bearings vs. a MAST table with only one actuator.
ISZ[/QUOTE]
Do you realize that the acceleration is 20.45g? Moving the weight will not be an issue. Controlling it will be. I would consider using two cams with the mass between the two cams. As the cams rotate the mass moves back and forth. The cams are geared together so they take turns pushing the load. This is obviously and 'old school' solution. It is simple but unfortunately not flexible.

A high tech solution would require getting a motion controller that updates very quickly, at least 2000 times a second, and controls an electric actuator. We can go as fast as 4000 updates per second. California linear devices makes some very fast actuators. A lot of energy will go into compressing and decompressing oil to get the required accelerations.

My quick calculations must be off, I was shooting for only 5-7G's @ 200Hz. On the good side it sounds like I only have to get up to 40Hz now that the NVH engineer has finally done his work.

And S04 was standardized under ISO 10372-04–04-0-92. The highest flow I have seen in this mount is 16gpm.

Thanks, ISZ

quote:

Originally posted by IceStationZebra:
My quick calculations must be off, I was shooting for only 5-7G's @ 200Hz.

The position as a function of time is 0.005*sin(2*PI*Hz*t)
velocity as a function of time is
2*PI*200*0.005*cos(2*PI*200*t);
The acceleration as a function of time is
(2*PI*200)^2 *0.005*-sin(2*PI*200*t)
Sine the maximum value of trig functionsi is 1 then the peak acceleration is simply
(2*PI*200)^2 *0.005
and the peak velocity is
(2*PI*200)*0.005
Test systems are not simple to design if you haven't done it before. That is why MTS charges what they do and I can't hold it against them because I know that half of our customer screw up their calculations and end up with expensive redesigns. We sometimes get called before the hydraulic design but usually we get called after wards because "the motion controller can't go that fast". This winds me up tight because we just shuffle around electrons. Another little known fact is that it takes 8 times as much power to cycle twice as fast. That takes many people my surprise.

A quiz. Why does it take 8 times as much power to cycle and 2 Hz vs 1 Hz if the amplitudes are the same? Can you prove it?

This message has been edited. Last edited by: Peter Nachtwey,

Sealum Industries makes transition plates for everything

quote:

And speaking of spools, one spool option for Moog 760's is a "Pc >80% of Pp". What is this?

Moog dist. says "linear flow spool with null pressure greater than 80% of system pressure"

Thanks for the info Doug.

Hopefully I will get back to this project in the next couple of days so I can answer Peter's challenge!

ISZ

Peter, I just wanted to let you know my employer decided that he could save money by eliminating my employment, so needless to say I am not motivated to solve this problem anymore.

Thanks for the help, ISZ