If this looks like an oversized nut cracker, then I need one

That would work, but seems overly complicated. Why not just set the product up in a support base and hit it with a pneumatic cylinder with a steel plate attached to the end of the rod? You can easily adjust the speed and force of the impact with a pressure regulator and a simple 3-way valve.

Hi,

I posted the question.

A pnuematic solution might be possible. I am not familiar with pnuematics.

One thing I didn't mention is that the unit under test must move at ~70 mph so that it's innards experience deceleration forces. So, it would have to be mounted to the steel plate you mention.

One important point is that the unit should not be crushed by the test rig. That is damage to the unit should be limited only to that inflicted by it's collision with the stationary object. I know, my own contraption violates this. One fix is to actually have the unit flexibility attached at the end of the lever in my drawing rather than on the underside. The same could be achieved with the pneumatic approach.

How common are such reciprocating pneumatic fixtures, what are they called, and can they perform this work on the order of 60 cycles per minute for a few hours?

Thanks,

Dave

I don't have the capability on this machine to draw it or to scan a drawing but my description will probably suffice.

Why not attach one end of an arm to the shaft of an adjustable speed motor.

Attach to the end of the other end of the arm a length of cable, chain, etc., whatever is appropriate, and to the other end of the chain a means of holding your test piece in an attitude so that when it is swung around it will hit an appropriately shaped and positioned hard surface. As it hits, because it is on a flexible length of whatever, it will work its way around the obstacle to come around for another hit, and another and....

j.

Thanks. I wonder how big an engine would be required to maintain the 700 RPM required to cause 70MPH collisions considering the drag of those collisions?

Dave

I suggest different approach:

Take a scrapped single cylinder diesel or petrol engine. Open the cylinder. Connect an electric motor to the shaft of the engine. Attach the unit to be tested to the piston of the engine and run it at required speed (found out from the calculations).

Keep some plate in front of the unit to impact on it approprately.

This will give you all your test conditions

As you can see in my previous mail, I already suggested this method but with an old piston air compressor, there is the motor mounted and everything ready to plug and play.

Yes jangkly. I do appreciate, you first suggested almost same method. Before putting my post, I did not go through all the posts.

This prooves that discoveries take place independently but simultaneously in the world.

Yeah..This is almost like when Mr. Bell stole the invention of the telephone from the other guy Whateverhisnamewas,

Oh! This is not fare. You are blaming me. Take it in good spirit. Please believe that I didn't read your post, before I wrote mine.

I grant you the patent of the idea, though I though similar thing parallaly.

Please read appendices of "Act of Creation" by Arthur Koestler, where he has given many such evidences of parallel discoveries. According to him, when the time is ripe enough for the discovery, discoveries take place at many places over the globe.

Don´t get me wrong, I was only joking. Interesting dude this Arthur Koestler.

This is a typical setup for a drop test on some or other equipment (electronic etc).

The spring is there to get the correct speed in a shorter distance.

What about something like a baseball pitching machine?

This was my first thought also. It would be easier to pay some guy to sit there and drop it in then build a contraption.

Or if you are into building something build a return track and loader for the pitching machine. Sounds easy to me......

Great idea - we've actually done that in the past. Problem is that the turning wheels chew things up quickly.

You could end up life testing the spring and/or pivots. 10k is not so much. How many to stress? How much time? Test to destruction?

They do destructive test on equipment to determine its value.

I have dropped my mobile phone a few times (and so have a lot of other) and it is still working (thanks to such tests).

I have a 2 way radio 5" long and just falling over caused the soldering to crack loose (thanks to not testing).

I bought a ASUS eee laptop and you really must see the testing performed on the design. (there is a video about it)

Your solution is more complicated than it has to be. Take a electrical-motor driven air compressor(buy an old one for 1/2 price), open the compressor and use the piston of the compressor to make the impact to your product. If you need you can make an extencion on the piston by drilling in the piston three holes and make threads and screw in long bolts perhaps with a plastic plate on the end to make wider "impact wall". NB. take care not attaching to much weight on the piston as it will un-ballance the compressor resulting in loud and ugly noise and shorten the lifetime of the bearings and all. you can fix this by adding more weight to the counter ballance weight.

This will give you, depending on the rev. on the motor used, a few hundred impacts pr. second so you maybe would like to slow things down with a motor drive.

You can then adjust the speed of the impact by adjusting the position of your product -easy to calculate.

Good luck

sounds lame to me also but could you find the right bridge/67th story or the perfect height to simply drop it?

just a few ideas.

The object should be float mounted and the travel of the beam should be limited to prevent squeeze.

A servo or stepper could be used to regulate the speed throughout the cycle. fast lifting may not be part of the test.

I've built one of your "nutcrackers" about ten years ago. I'm replying from my home desk and don't have the exact reference books here to quote.

Look up SAE handbook "vibration testing machines" and you'll see what you're after.

Motor driving a "lifting cam" and adjustable springs to pull your item under test into a stationary target item with a hard stop to stop overtravel (crushing) as you described.

The most challenging part was to vary the motor speed.

SAFETY GLASSES AND HEARING PROTECTION IS REQUIRED!!!!!!

Watching the catastrophic failures can be very theraputic.

Why not just put the Unit Under Test in the bottom of several nylons (stockings), and tie the top of the nylons to a rotating arm. The UUT should bounce off and swing past the striking surface before starting its next full circle.

Watch out: although my idea is very amateurish, nearly all the other ideas here (including your own) end up crushing the sample between the striking surface and the actuating device. With this scheme you get the required slam. Text reads: Counterweight, Axle, 3 foot arm, 6 inch sample "sack" and striking surface.

With these dimensions you would need 4 revolutions per second to achieve the required 60 mph.

This approach is appealing in its simplicity and offered by a few contributors. How powerful a motor will be required to sustain the 60-70mph impacts?

You should employ this dog!!!

Another thought, would it be easier to hold your product still & repeatedly hit it using a ram, pneumatic, hydraulic or electric.

That is hilarious!!

Do you have hydraulic capabilities at you test lab? If so check some equipment by MTS. You can do what you are looking for and obtain feedback as well. I have designed and built equipment similar to your needs in the past and you may be able to do the same. National instruments makes PC cards and programs that can control and acquire data for your test while it runs. I do not think you will have the control and speed that you require with a pneumatic test stand.

Perhaps a trebuchet or pitching machine would also work. 60mph is quite fast for the limited accelleration of a small spring. However both are impractical for the repeated impact.

Hitting with a spring-loaded triphammer would work as well, and much easier to repeatedly impact. I used to do this with glass testing, albeit at lower impact levels, and with a "home-made" weighted hammer with a foot-pedal release and many fewer impacts.

It's important the surface hardness and shape it impacts (metal/hard plastic/wood/?). Flat hammer face, sphere like a billiard ball, pointy like a metal punch.

Is it important that the object be held in place during the impact (hammer-crushed), or must it be allowed to bounce/resonate/fly (golf swing). Something to think about. Whetever the system you decide upon, make it test what needs to be tested, not something else.

Also the possibility that I could place it between the wall and my head at work on a bad day;}

Mag

Consider this:

An electric motor with a flywheel about 36" diameter with a cover over it. A shute on the top and one at the bottom. They are both just a bit larger in diameter than the ball you are testing. The top shute is the delivery shute and the bottom is the return. The ball will be "flung" against a nearby wall, fall to the return shute below, enter the bottom of the spinning wheel and be accelerated around the wheel and, again, "flung" against the wall.

I am not certain if you can accomplish one "fling" per second, but, with some speed adjustment, you just may be able to do it.

This is similar to our previous "pitching machine" approach. The flywheels tend to chew up the product so we are looking for a better method. Thank you!

What you are looking for is a test lab with a hydraulic or electrostatic (voice coil) vibration test jig. Voice coil machines can also do vibration testing at much higher frequencies than hydraulics can (hydraulics are limited to about 500 Hz max). Hydraulics on the other hand can expose the DUT to much higher amplitudes within it's frequency spectrum capabilities. Hydraulics can also handle much higher DUT weights than voice coils. The mounting fixture design is very important because you do not want harmonics from the test fixture altering the energy input into the DUT.

That said, where I used to work. We had an electrostatic one that could handle down hole tools that weighed around 150 lbs and we could go as high as 20Khz at 1G and 20G's at around 150 hz if memory serves. it was made by Ling in Anaheim CA. But there are a lot of manufacturers listed in Globalspec if you want to buy one. There are a lot of testing labs that will rent time to you for your test. Southwest laboratories in San Antonio is one we used when ours was down or overbooked.

Maybe a person could come up with something like this:

Think on the line of a paint-ball gun or a potato gun. Pressure, length of barrel and steel plate would have to be adjusted to accomplish the speed needed and withstand the testing abuse.

The barrel would be elevated to return the item to the firing position. The higher the elevation the faster you could cycle the test.

Neat drawing - I have imagined such a solution just like this. However, with no pnuematics/hydraulics/fluid mechanics experience I have no idea of what this type of equipment is capable of. Can the air compressor recharge quickly enough for repeat shots every 5 seconds or less? Preferably in less than 3 seconds. Can the valve triggering be electronically controlled? Where do you find these parts?

Thanks.