Need help on Drop Testing & Equipment

[BretMan]

Hello,

If this is the wrong forum for this question please correct me.

I need to conduct some drop tests on a device about 1ft. sq. and weighing about 5lbs. I'll be testing impact forces but I only need to go between about 10Gs and 200Gs. The equipment just needs to tell me what the G reading is at impact given drops from different heights. I can easily make the necessary jig with a ramp and roller guide bars.

My question is for a solution to find inexpensive (used is fine) equipment to do this. The least expensive I've found online is about $1200 (new) for an accelerometer connected to a PC with an associated program, which is about twice as much as I can afford right now. I've had no luck finding used alternatives.

Any suggestions are very appreciated. I'm willing to make one out of parts you may recommend as long as the results from the readings are reasonably accurate, consistent and the reading display, whether mechanical or electronic, "holds" the reading until it's re-set. Thank you.

Bret

Miami,FL USA

 

[rb1957]

if you have to measure acceleration (or in your case, deceleration) you need an accelometer.

what if you measured the peak force instead ? that would be much easier, a quick registering scale, and maybe a video camera (loaned from some parent!) to record it ??

 

[IRstuff]

Depends on what you want to do with the data. If all you're interested in is some gross information, then a force measurement might be OK. However, if you want PSDs and the like, then you need accelerometers. Moreover, you generally need to have all 3 axes, unless you are just that good at dropping thing EXACTLY on the sides.

TTFN

FAQ731-376

 

[BretMan]

Thanks for the suggestion. I hadn't thought of that. Is a "quick registering scale" a bathroom scale? If so, I don't think that would be presentable for the needed convincing data I'll be gathering. I definitely need to have a display reading sudden deceleration in g-forces. I can't be the only person in this situation. There must be many places that sell used measurement equipment for drop testing - I just don't know of any.

Bret

Miami,FL USA

 

[unclesyd]

These are just a few of the devices to measure impact on shipping containers. Some devices are relatively inexpensive and I believe that they will do what you require.
We use to use them as one shot deal.

http://www.isthq.com/Products/tabid/582/Default.aspx

http://www.gtbcases.com/category/4719/impact-indicators.htm

 

[MintJulep]

Have you thought about contracting out the test, or renting equipment.

A load cell under the target plate: F=ma

High-speed video: Differentiate a couple times.

Off-the-wall idea: One of those "radar" baseballs. (I doubt that it's up to 200G)

 

[FeX32]

rip the accelerometer our of you iphone and recalibrate it....


Fe

 

[unclesyd]

Here is one the site who's equipment I think we used. They have pretty good cross section of equipment with all the ranges you should need.

http://www.shockwatch.com/shipping_handling_monitors/impact_indicator/selection_guide.php#SWMag

 

[BretMan]

You guys are great! Thanks for those ideas. I've emailed each of the company links and am waiting on their replies.

Regarding the baseball idea, I think I've seen those on TV. I'm pretty sure they're designed to measure the speed of the ball, not the measure of G's with a glove or bat.

Regarding the iPhone, I'm pretty sure the accelerometer in them (I don't own one) is for motion sensing, just to keep the screen oriented horizontally for the user.

Regarding the 3-Axis accelerometer, those are more than what I need as I just need to measure impact in one direction. Plus they're expensive.

The range I need of less than 200 G's is tough to find. 1K, 5K, 10K accelerometers are available. DigiKey has a good selection too but I'd have to do all the electronic connections to those, which I don't know how to do. I also looked into G force instruments for airplanes but they only go up to about 10 G's max.

If you have more ideas, please let me know. Otherwise I'll get back with feedback from the links. I'm also going to contact UL and Consumer Reports but I'm sure the ones they use are very high end.

Bret

Miami,FL USA

 

[MintJulep]

Regarding the baseball idea, I think I've seen those on TV. I'm pretty sure they're designed to measure the speed of the ball

And how do you think it does that?

 

[unclesyd]

The link that I posted to Shock Watch has impact indicators that range all over the map. Some are single axis or jsut impact indicators.

 

[flash3780]

Once you have the G's of deceleration, what are you going to do with them?

 

[IRstuff]

I don't get what the problem is. Digikey lists an Analog Devices ADXL001 with +/- 500g range for about $60 and there's an evaluation board for about $80:

http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=ADXL001-500BEZ-ND

http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=EVAL-ADXL001-500Z-ND

TTFN

FAQ731-376

 

[BretMan]

I'll check with Shock Watch on that, thanks.

If the accelerometer in the baseball is for providing a reading of it's speed, that won't help me for my need, I need a G force reading at impact. Yes, it has an accelerometer, probably similar to ones that can be put into cars to measure it's 0-60 time or cornering G's but those aren't the readings or the range I need. There are different ones for different purposes all having to do with reading motion of some kind. For example the 3 axis ones are used a lot for measuring machine vibration because the vibrations can come from different directions. The less vibration, the less friction and the longer the machine will last. The iPod one detects tilt position, others can be placed into artillery shells and measure huge G numbers. All measure motion but for different applications.

Bret

Miami,FL USA