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Author Topic: Recording laser tachometer for automated spin-decay curve capture  (Read 316 times)

Jeremy McCreary

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A while back, ortwin pointed me to the UT372 recording laser tachometer as an affordable solution for automated spin-decay curve capture. You can download the PDF manual and Windows software at this link for inspection if you like.

Got the red UT372 below for $66 on Amazon. Seems to be well-designed and well-made. Tested the USB recording functionality for the first time today, and I'm happy to report that it works just fine on Windows 10!



After opening the bare-bones software on my laptop and connecting to the UT372 via the included USB A to USB B cable, I spun up the top shown and started collecting (time,RPM) data points at 1-second intervals. (The sampling rate is adjustable.) Then I exported the data to a file for processing in Excel.



The export files bear ".xls" extensions but are really tab-delimited text files, not Excel files per se. Nonetheless, Excel will open them after some complaining. Another 5 minutes of work, and I had this raw spin-decay curve and exponential fit (dotted line). The blank RPM values in the table were obvious outliers that I deleted manually to keep Excel from plotting them.



Plan to use exponential lifetime as a figure of merit for comparing top performance going forward. This top's 46.3 s lifetime is very short by endurance top standards. But over my entire LEGO top collection, it's pretty middle of the road.

Still streamlining my workflow with it, but you can get an idea of what's involved from this video...

https://youtu.be/jIXdYjuObiw
« Last Edit: June 08, 2021, 07:02:47 PM by Jeremy McCreary »
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ortwin

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Re: Recording laser tachometer for automated spin-decay curve capture
« Reply #1 on: June 08, 2021, 02:31:49 AM »

Great to hear that it does what it should!
So that bicycle courier from China was going fast to deliver it to you?
A few days ago,  I promised myself I will also order one as soon as I reached my 25 minutes goal. 
That thread on the back for the tripod sounds good also. My current tachometer also has one, but it didi not come with one. My friend suggested it and made it. It proved extremely useful ever since. Could you just drop a quick picture of the backside with that "threaded metal hole" visible? You could just modify the first post, I will find the picture.
Thank you for the review!

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ta0

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Re: Recording laser tachometer for automated spin-decay curve capture
« Reply #2 on: June 08, 2021, 09:28:26 AM »

Having entered decay data by hand in the past, I fully appreciate the usefulness of a data logging tachometer. I've got good and bad stuff from China, so thanks for taking the risk for us.
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Jeremy McCreary

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Re: Recording laser tachometer for automated spin-decay curve capture
« Reply #3 on: June 08, 2021, 07:03:47 PM »

The back of the UT372 has a brass hole with a standard 1/4"-20 tripod thread.

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Jeremy McCreary

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Re: Recording laser tachometer for automated spin-decay curve capture
« Reply #4 on: June 08, 2021, 08:48:33 PM »

Having entered decay data by hand in the past, I fully appreciate the usefulness of a data logging tachometer. I've got good and bad stuff from China, so thanks for taking the risk for us.

The Chinese seller on Amazon opened the package before shipping and removed the software and 4 AA batteries listed as "in the package" in the printed manual that came with the tach.

After calling them on it, they offered me a 60% refund if I'd agree not to return it. Since the tach itself looks new, I accepted. That was yesterday. We'll see if and when the refund appears in my account.

Fortunately, you can download the software, and there are several other sellers on Amazon.
« Last Edit: June 08, 2021, 08:54:43 PM by Jeremy McCreary »
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ortwin

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Re: Recording laser tachometer for automated spin-decay curve capture
« Reply #5 on: June 21, 2021, 08:41:09 AM »

. ...I promised myself I will also order one as soon as I reached my 25 minutes goal....
I did not order mine yet because  I still did not reach my 25 minutes goal.
But I am positive that I will get there eventually, so I want to suggest to you, Jeremy, already to think about "standard settings" each of us should use so that the data and the curves can be compared easily. Maybe even some template, excel or something, where we can bring our measurements in to?
Some fields would be needed to be filled in: time, date, location, equipment, author, comments, ....

Does that make sense to you? It would be better to have that at the beginning before everyone has 50 files but comparing the files to those of other people becomes unnecessarily hard due to small incompatibilities.




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Jeremy McCreary

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Re: Recording laser tachometer for automated spin-decay curve capture
« Reply #6 on: June 21, 2021, 12:32:50 PM »

...think about "standard settings" each of us should use so that the data and the curves can be compared easily. Maybe even some template, excel or something, where we can bring our measurements in to?
Some fields would be needed to be filled in: time, date, location, equipment, author, comments, ....

Does that make sense to you? It would be better to have that at the beginning before everyone has 50 files but comparing the files to those of other people becomes unnecessarily hard due to small incompatibilities.

Wow, having 50 raw spin-decay curves (SDCs) to analyze and compare -- beyond my wildest dreams!

Ideally, we'd use Excel files to share the raw (time,speed) data so that anyone could analyze it.

Personally, I'd find the following useful:
1. Experimenter's name
2. Date data was acquired. Time if necessary.
3. Name of top.
4. Enough low-res photos of top to show its shape and aerodynamic properties.
5. Top description, including any noteworthy features not clear from photos.
6. Pertinent top dimensions, with reference to photos as needed for clarity.
7. Known or estimated mass properties, including mass, CM height, and moments of inertia if known.
8. Tip details, including material and estimated radius of curvature over contact patch.
9. Plot of raw SDC in RPM vs. seconds.

I'd really like the graph to include an exponential fit -- including the associated decay constant or lifetime and R² goodness of fit. I think we'll learn a lot from seeing how much the measured SDCs differ from their best exponential fits.

Finally, would love for all data other than speed (in RPM) to be in meters, kilograms, and seconds for direct comparison and easy analysis without conversions.

Likelihood of getting even half of that wish list = zero, but a template might help.
« Last Edit: June 21, 2021, 09:22:49 PM by Jeremy McCreary »
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ortwin

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Re: Recording laser tachometer for automated spin-decay curve capture
« Reply #7 on: June 30, 2021, 02:41:49 PM »

Received mine today.
Mostly everything works fine as far as I tested.
The thread for the tripod is a bit far off center. That makes it too unbalanced for my little tripod: It tilts to where it wants to, not to where I put it. So I need to use my large tripod.
Other than that it is Like Jeremy said a matter of streamlining the work with it.@Jeremy: did you by any chance prepare a template for SDCs?I think we should also agree on some sampling rate. What would you recommend from your experience so far?

« Last Edit: September 19, 2021, 01:24:51 AM by ortwin »
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Jeremy McCreary

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Re: Recording laser tachometer for automated spin-decay curve capture
« Reply #8 on: June 30, 2021, 05:37:11 PM »

Received mine today.
Mostly everything works fine as far as I tested.
The thread for the tripod is a bit far off center. That makes it too unbalanced for my little tripod: It tilts to where it want to, not to where I put it. So I need to use my large tripod.
Other than that it is Like Jeremy said a matter of streamlining the work with it.@Jeremy: did you by any chance prepare a template for SDCs?I think we should also agree on some sampling rate. What would you recommend from your experience so far?

I'm having good luck with a short, highly articulated Delkin bipod with big suction cups for feet. Bought it years ago for my heavy DSLR but never found a good use for it till now.

You and Iacopo might settle on a sampling interval, but it would surely be way too long for most of my tops. So far, I've been using 1 s.

A more practical sampling standard would be to collect ~100 samples per SDC. That should provide plenty of resolution for our purposes.

Might start on a template next time I measure a batch of raw SDCs. But you said your spreadsheet skills are poor, and I don't know where Iacopo stands in that regard. So, realistically, who would use it?

Also, some potential SDC providers may not have Excel. If free web-based Google Sheets can import the data files and has the necessary plotting and curve-fitting functionality, might be a better alternative.
« Last Edit: June 30, 2021, 06:30:12 PM by Jeremy McCreary »
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