Home Made Bearpaw Spine Tester

dvd8n

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I have purchased a couple of 1kg cells as the nearest I could get to see if I can resurrect my device, might decide on a more powerful CPU as well so I have control and write my own code.
Does the Bearpaw have facilities for the user to calibrate it?
 

dvd8n

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Good thought, it is more like 9mm, sorry the unit is currently in bits but it is well short of 12.7mm
That'll be why they can get away with 750g ones. 👍

By the way, mine were all etched with their range on the bar so yes, the Bearpaw ones will probably be 750g.
 

malbro

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At 28" and 1/2" depression you will, as you say, get 440g load on each cell from a 500 arrow. But remember that the 1/2” depression is used for all arrows so a 250 arrow will impart 880g force on each end, which blows the 750g limit of the cells by a fair margin. 250 arrows aren't common but they do exist. Is the depression used by the Bearpaw less than a half inch by any chance?
From the bearpaw manual,
Do not overload the arrow rests in excess of the maximum load of 750g each.
 

dvd8n

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From the bearpaw manual,
Do not overload the arrow rests in excess of the maximum load of 750g each.
Well, that fits with the 750g rating of the strain gauges.

Mind you, I don't know how you're supposed to know if you're going to exceed that rating without knowing the spine of the arrow that you're about to test...
 
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dvd8n

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Only to tare it, hence my thoughts to write my own code, the Arduino libraries are pretty comprehensive.
If you want a copy of my code to get you going then let me know.

It needs a re-write as it was written simplistically as a proof of concept that got out of hand and it's not how I'd do it now that I know what I'm doing. But it works.
 

malbro

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Just found some 750g ones on amazon, uxcell 750g Weighing Electronic Balance, the 1kg ones where much bigger but these are the same size as the originals.
 

dvd8n

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Just found some 750g ones on amazon, uxcell 750g Weighing Electronic Balance, the 1kg ones where much bigger but these are the same size as the originals.
That looks like a better bet; you could just swap them in with minimal drama.
 

malbro

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If you want a copy of my code to get you going then let me know.
I would be interested in what you have done so far, I am still interested in customising the device for my own purposes especially as the app they provide, has to be connected to collect the data. Using a more powerful CPU I can stream the data to SD card and then analyse on a PC that way it is independant of the PC, also with something like an ESP32 I can WiFi the data.
 

dvd8n

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I would be interested in what you have done so far, I am still interested in customising the device for my own purposes especially as the app they provide, has to be connected to collect the data. Using a more powerful CPU I can stream the data to SD card and then analyse on a PC that way it is independant of the PC, also with something like an ESP32 I can WiFi the data.
No problem; I'll post it here when it's in a fit state. Bear in mind that with an Arduino you get a USB interface for free; if you can figure out the data format you could maybe use their app. I don't suppose that it's complicated...
 

malbro

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No problem; I'll post it here when it's in a fit state. Bear in mind that with an Arduino you get a USB interface for free; if you can figure out the data format you could maybe use their app. I don't suppose that it's complicated...
I do have a usb monitor and can see the messages to and from the PC to the analyser but until it is working all I get are the connection messages.:cry:
 

dvd8n

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Well, I think that the spine tester is pretty much finished:

IMG_20210520_164639.jpg

The mechanics are finished, electronics are permanently fitted, the wires are properly secured and the software is good enough. Even the DIN socket has been flipped over so it's the right way up.

It's hugely over-engineered but at least I know it'll survive an apocalypse. Maybe the descendants of the cockroaches will have fun trying to figure out what it is.

To take a reading you press the arrow down onto the central pillar and read the spine from the display:

IMG_20210520_164730.jpg

It reads the modern 1.94lb at 28" spine as listed on most modern arrows by default:

IMG_20210520_164934.jpg

But will also give the older 2lb at 26" centres reading (without adjusting any of the mechanics; it's an arithmetic transformation):

IMG_20210520_165231.jpg

although I don't know if anyone is really interested in this older standard of spine reading.

It'll also do the poundage reading for old-school guys:

IMG_20210520_165330.jpg

I have to admit that I don't really know how accurate this reading is.

At the press of a button it'll average the last six readings and tell you the direction of the maximum:

IMG_20210520_164852.jpg

The code assumes that the last six readings were taken on the same arrow 60 degrees apart (ie on the vanes and half way between them). All my fancy ideas of taking a small number of readings and the software magically working out all this stuff itself came to nothing. But hey, at least it saves you hunting for a biro and a notepad.

It'll also weigh an arrow:

IMG_20210520_165601.jpg

although only to gram precision so I'm not really sure how valuable that is. I suppose given that it knows the front and rear weights separately it could do a FOC calculation too. There's a project for the next time that I throw my back out.

Being a homebrew item the gauges need calibrated:

IMG_20210520_165045.jpg

It's not too big a deal to do; it's really just a case of putting a known weight on the gauges; it just takes a few minutes. Once it's done it saves the calibrations in EEPROM so in theory it's a one time only thing but in practice you need to re-do this whenever you fiddle with the mechanics. And let's be honest - this is a fiddling with project. Nobody's going to trust their arrows to my shonky software and worse electronics.

The height of the centre pillar needs adjusted after it's been apart too:

IMG_20210520_165507.jpg

This is done with my trusty (and cheap) 1/2" ball bearing. At 99p it may be the only bit of this project that made financial sense.
 

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malbro

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This is my code if anyone wants to have a laugh.
Thanks for posting, looks to be well documented, my replacement weigh bars arrived today, they look exactly like the originals even down to the holes through the bar and the fixing points so a direct replacement.
 

dvd8n

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Thanks for posting, looks to be well documented, my replacement weigh bars arrived today, they look exactly like the originals even down to the holes through the bar and the fixing points so a direct replacement.
No problem.

I was looking again at the photos that you posted the other day and I don't know if it's just camera angles but one of the bars looks a little distorted. I wonder if that is your issue?
 

malbro

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No problem.

I was looking again at the photos that you posted the other day and I don't know if it's just camera angles but one of the bars looks a little distorted. I wonder if that is your issue?
The screen lights up and requests I place an arrow on the device but there is no response when an arrow is placed on the rests, it could be a faulty sensor as they are very sensitive and should not have a load exceeding 750gm on either sensor, but as there is no indication that the analyser has even seen a signal on just one sensor (which could be used to raise an alarm) it is either both sensors or the HX711 boards. I have two new sensors and two new boards so hopefully I can check it out this weekend.
Once I get it working I will look at using an ESP32 board to provide WiFi connectability to the device. I spent an hour or so on your code and it looks like it can be ported to an ESP32 so that will be my next project to fit in with my day time job.
 

dvd8n

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The screen lights up and requests I place an arrow on the device but there is no response when an arrow is placed on the rests, it could be a faulty sensor as they are very sensitive and should not have a load exceeding 750gm on either sensor, but as there is no indication that the analyser has even seen a signal on just one sensor (which could be used to raise an alarm) it is either both sensors or the HX711 boards. I have two new sensors and two new boards so hopefully I can check it out this weekend.
Once I get it working I will look at using an ESP32 board to provide WiFi connectability to the device. I spent an hour or so on your code and it looks like it can be ported to an ESP32 so that will be my next project to fit in with my day time job.
When I damaged one of my bars it was still giving readings, they were just obvious nonsense. So your problem sounds different.

The code is probably reasonably portable as it mainly uses standard libraries. A note about the libraries - some of them behaved a little oddly when I tried to create objects dynamically or got too ambitious with inheritance and the like. So the structure's not always the way I'd like. But debugging inheritance problems with printfs isn't my idea of a good time so ... it is what it is. Oh and I'm aware that the display code isn't my finest - it sort of grew. But you'll probably rip that out anyway.
 

malbro

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When I damaged one of my bars it was still giving readings, they were just obvious nonsense. So your problem sounds different.

The code is probably reasonably portable as it mainly uses standard libraries. A note about the libraries - some of them behaved a little oddly when I tried to create objects dynamically or got too ambitious with inheritance and the like. So the structure's not always the way I'd like. But debugging inheritance problems with printfs isn't my idea of a good time so ... it is what it is. Oh and I'm aware that the display code isn't my finest - it sort of grew. But you'll probably rip that out anyway.
With an ESP32 I can set up an AP and use web browser technology for display, I will let you know how I get on.
 
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