Seismic Shake Table - Help For A Non Mech Guy 1

[sticksandtriangles]

I want to make a semi-pro level seismic shake table, but I have no clue where to even start.

What I what:

- Motion control in the x and y direction​

- Motion control in the vertical direction if at all possible, but very willing to settle with motion in just the x and y​

- I want to be able to program an arduino/raspberry pi type element that can read displacement/velocity/acceleration vs time data and move the shake table accordingly​

- I was thinking a scale of around 4'x4' but willing to work with this dimension. Still not sure the weight that I would be pushing, but the weight of the structure above would probably be 10 lbs and the subassembly being shaken below would be 20 lbs if I had to guess.​

I have started to do some preliminary research on this topic and this website with actuators looks promising:

https://www.actuonix.com/category-s/1934.htm

Speed:

https://www.youtube.com/watch?v=NOupeajCX-0

Programmable:

https://www.youtube.com/watch?v=g-1Sx5ckEt0&t=213s

Questions that I have though are the following:

- These actuators do not look to move fast enough to capture the fast ground shaking that an earthquake typically represents (I would love to be able to input an El Centro type ground motion into this thing

http://www.vibrationdata.com/elcentro.htm.

Are there any actuators that move this quickly?​

- How programmable is this actuator? Can I input lots of data and get this thing to respond properly under crazy earthquake accelerations​

- Is there any other product I should look into? Let's for now assume budget is not a concern... feel free to fire away with thousand dollar ideas​

Appreciate the thoughts!




S&T

 

[sticksandtriangles]

IRstuff,

The only fascination with the lead screw was the wide price difference... You may have convinced me though that using a lead screw is like trying to fit a square through a circular hole. The actuator I linked though claimed to fit the bill though... but I was just dealing with sales people I am sure.

Seems like to get back into a reasonable price range for the voice coil actuator, I need to compromise stroke length to be in the range of 1" as compared to the 4" I was targeting. I think I could live with that as long as I can get my acceleration and velocity targets.

glass99,

in order of importance 1. be really cool, 2. inspire youngsters .
I think I am going to go down the voice coil route and forego the geared screw idea all together. I will have to research how to control the voice coil actuator as well. I guessing each company produces some piece of software the controls vibrations, speed, etc.






S&T

 

[glass99]

the other thing to take into account would be the actual natural frequencies of the models you will put on the shake table. A real building may have a first mode in the range of 2Hz, but a scale model would be faster wouldn't it?

 

[sticksandtriangles]

That's a good point glass, I was thinking that maybe the loss in stiffness to loss in mass would be proportional?

freq = sqrt(k/m)

I should probably build a quick test model in a analysis program to see if this holds true

S&T

 

[glass99]

what would be cool as a demo for the kiddos would be to show that skyscrapers have low frequencies and are therefore safe, and short stiff buildings like NYC brownstones made from brick are unsafe. How will you build your skyscraper? Could you rivet together aluminum strips with angle brackets? You could probably get a model dialed into what frequency you want with some lead weights, then remove the weights to show the effect on frequency and therefore seismic response.

 

[sticksandtriangles]

That was goal glass99, have a tall guy that responds very little to fast excitations, and a short stiff guy that falls over.

S&T

 

[glass99]

also, why do you need the model to be 20lb plus for this? its all going to be much easier with the voice coil etc if its like 2lb. I mean you gotta schlep this from your car into the schoolhouse too. High frequencies and long strokes will imply a high power device which really ups the difficulty level. You want to build this with arduino bits and 24V or less power.

 

[IRstuff]

Seems to me that you are conflating "short" with "stiff," which is only true of brick/masonry construction. Wood-frame houses tend to survive earthquakes tolerably well. A better demo would be two-story wood-frame vs. two-story masonry construction.

TTFN (ta ta for now)
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[glass99]

the peak of the seismic spectrum is at higher frequencies (~10Hz - 2Hz) which covers most houses. Yes properly built timber is much better than unreinforced masonry because it has tension strength and ductility. Skyscrapers have a first natural frequency of about 0.1Hz which is way down the spectrum in terms of acceleration, but the cool thing demo-wise is they sway by a lot. I worked on a building in LA which moves by +/-30ft in a design seismic event (ie 60ft total).

 

[fel3]

I don't know what the prices are, but I found this using the search term "portable shaker table structural engineering":

https://www.quanser.com/wp-content/...ables-and-Smart-Structures-Datasheet-v1.6.pdf

This also came up on the first page of my Google search, but I don't think it's what you want:

https://vermontwoodsstudios.com/cat...MIhaHty6Cm5AIVsCCtBh1lrwnfEAMYAiAAEgJWJfD_BwE

I guess "shake table" would have been a better term than "shaker table."

==========
"Is it the only lesson of history that mankind is unteachable?"
--Winston S. Churchill

 

[sticksandtriangles]

Those quanser ones are in the range of 20k. Where's the fun in buying one that just works.

S&T

 

[fel3]

20k seems a bit high. 19k would be more reasonable.

==========
"Is it the only lesson of history that mankind is unteachable?"
--Winston S. Churchill

 

[glass99]

I just bought a hobby grade CNC router for $200. It has an X-Y table that moves back and forth pretty quickly. You could program it to shake fairly easily, and it would be easy to try to see if it actually works for school demo purposes.

https://www.amazon.com/Genmitsu-301...nsmart+router&qid=1567030045&s=gateway&sr=8-1

 

[sticksandtriangles]

I think I will be pulling the trigger on one of these guys:

http://www.beikimco.com/motor-products/VCA-voice-coil-actuator-developers-kit

The developer kits looks easy to program and I like that this is one stop shopping for a controller and feedback mechanism.

Thanks for all the assistance on the thread, I think the voice coil actuator will be a good investment over the geared actuator.

S&T

 

[MintJulep]

Shaker tables are anchored to a solid foundation because Newton.

Difficult to reconcile with portable.

 

[sticksandtriangles]

I don't think this thing will be too difficult to hold down, get some locking wheels and it should be fine

S&T