SparkFun selling load cell possibilities

https://www.sparkfun.com/products/13230

https://www.sparkfun.com/search/results?term=load+cells

I might buy a loadcell and amp from them in the next year, awesome stuff!
For right now though, the two half-bridge strain gauges and arduino that I'm working with are good enough. I hope to build thrust-meter with them, but these would definitely be a step up for my efforts.

I wonder how many other people on here have done a similar project?

I have a couple load cells and a National Instruments Fieldpoint strain gauge reader module. Haven't gotten around to the test stand project though.

I have two load cells / strain bars. I've thought about mounting a launch rod through them and making a reader of how much force the rocket puts on the rod on a windy day. In the x-y directions, at least.

Charles_McG said:

I have two load cells / strain bars. I've thought about mounting a launch rod through them and making a reader of how much force the rocket puts on the rod on a windy day. In the x-y directions, at least.

Click to expand...

That sounds like an outstanding NAR research competition entry...

Did anyone read the sparkfun specification sheet? There are only 2 sampling rates: 10 Hz which is worthless and 80 Hz with is still very slow for obtaining motor thrust curves.

Bob

While those aren't good for motor testing, some might find other uses. And they could possibly use a different amplifier to get faster sampling.

I'm using an HX711 in my thrust stand, although I didn't buy the breakout from Sparkfun. It's nice to see them make one though.

The 80 Hz depends on using an optional externa crystal, which the SF board omits. The part can run on internal oscilaltor, and I'm getting over 100 samples per second with it. It's possibe that other samples err on the slow side and produce a rate lower than 80Hz. Datasheet is here: https://www.dfrobot.com/image/data/SEN0160/hx711_english.pdf

HX711 is a very common part. Its purpose is to go into kitchen, bathroom and desktop scales. While fancier parts are definitively available, the results I'm getting are interesting enough for me.

Here's a 38mm 1G sugar motor I burnt recently.

Ari.

I should add that this is raw data with no filtering.

Ari.

Here's a 38mm 1G sugar motor I burnt recently.

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That's a sugar motor? Sure doesn't look like one with that flame. What are the x and y axis references, seconds and pounds?

Steve G

Straight up 65/35 KNSB. The axes are seconds and newtons. If it were pounds... that would a heck of an achievement to pack that much impulse into a 1G 38mm :=)

I'm curious about your comment on the flame. I wonder what flame you expect on a sugar motor.

Ari.

Usually you don't see any flame especially in broad daylight. Was that an endburner?

Steve G

iter said:

I should add that this is raw data with no filtering.

Ari.

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That's not correct. All sigma-delta converters average data. That's how they work, and it the only way you get 24-bits.......or real data.

The problem with this chip is there is no indication on what the chip is doing. Take a look at any Analog Devices sigma-delta converter and you get a very detailed data sheet that tells you exactly what it's doing and how to modify the processing. For ~$55 you can purchase an AD sigma-delta converter on a demo board with software for a plug and play digital LCA. The only item I would add would be an external USB cable extender since I don't want my notebook within 10' of a test stand which is the limit of a USB link.

Bob

There's a data sheet in the documents listing below the YouTube video. Should be adequate.

Steve G

bobkrech said:

That's not correct. All sigma-delta converters average data. That's how they work, and it the only way you get 24-bits.......or real data.

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I see what you're saying. My statement is about my processing. I apply no additional filtering on top of what the chip does.

Ari.

sghioto said:

Usually you don't see any flame especially in broad daylight. Was that an endburner?

Steve G

Click to expand...

Yes, an endburner. You deduce that from the flame? :=)

Ari.

From the thrust curve.

Steve G