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#61
dstevens

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Random thoughts...

 

Hardware and PCB fab is my strong point.  I know just enough Python to break Andrew's code.   :buried:

 

The HX711 is an amplifier.  It takes low level signals from the sensor and amplifies them so the controller has enough voltage to read the input so any like amp will work.  The calibration should take take this into account.  What matters is a solid voltage delivered to the controller that can then be read by the controller and use that value as a variable in the software.

 

The sensors can be added in parallel so in this config using multiple sensors will appear to the controller as a single load.  That's how your bathroom scale works.

 

To account for the differences in load cells and pad design it will need some sort of weight based constant calibration routine.  In a mass produced scale with a consistent design and supply chain your variables and constants in the parts are know.   Those can be programmed into the design and used with minimal input from the user.  This is largely due to using a consistent load cell with known values.  For example you know 0 volts from the cell is 0lbs but you don't necessarily know how a particular sensor outputs at a given weight.   Guys like Longacre use the same cells in a production run of a specific model so they know that at 100 lbs (or whatever the weight is) the voltage from the sensor is X volts.  They then use that value as a basis for calculation.

 

How this sort of project competes on cost isn't being built as a one off.  Following the open hardware model vendors buy in bulk and provide kits the end users assemble.  That's what we've been doing with 3D printers and desktop/small format CNC for a while. The kit integrators package instructions, source code, files, etc so that you can either buy a kit or make one yourself.  That's how open hardware works.  As a kit integrator you are selling quality parts, assembly support in terms of documentation and moral support.  At this point we've sold parts and full kits for more than 10k machines.    Here's an example of the kind of assembly docs a kit integrator may provide.  http://roaddoglabs.i...addog_Labs_Bart  I'm not into this project to make kits necessarily it's because I think the hardware is cool and others could benefit regardless of anyone selling kits.  In some more vertical market projects group buys can take the place of kit integrators.  

 

In terms of competition driving price points that's what happened not only with printers but with routers, low power laser cutter/engravers and mechanised plasma cutting.  Printers that 7-8 years ago that were $10k lost out to machines that cost a fraction of that once the patents expired and the Reprap movement started pumping out open designs.  It's to the point now where cheap imports have flooded the market and displaced most kit integrators.  In fact we've stopped building full kits and now mostly sell parts and frames for the cheap import kits.  The race scale market is much more narrow than the desktop/hobby CNC market so the units aren't likely there but the desire is.  

 

It won't drive costs down so much on the low end as it will in the mid and high end.  Things like multi cell pads, wireless systems, integration to setup software will scale down in costs much more than an entry level scale kit.  It should be to the point where you could upgrade your current system using your existing pads with the Open Race Scales controller and software systems.



#62
dstevens

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The first batch of prototype boards went into production.  We should see them in a week to 10 days.  Contact me if you are interested in one as I have a few to distribute.  The only prereq is you need to be able to source the parts and assemble yourself and provide feedback and testing.  I'll generate a BOM in a bit but it's basically 18 various headers (10 if you solder the HX711 carriers on the board).

 

 

35304852362_f6a27b7330.jpg


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#63
Ron Alan

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Great to see you back and contributing Jackson!(only a few will remember that reference!)

 

I think I drew something like that when I was 7 on my spirograph! And it made just about as much sense to me then as well  :)


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#64
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There was a Spec Miata at the June Sprints with the hard top printed circuit board wrapped.


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#65
Andy Mitchell

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Hi all,

 

I did a bit of digging around and found some info on commercial pad design that *might* be useful to the movers and shakers behind this project. It's out of an on-line catalog, and I had to just grab it as a series of screen shots that I glued together into a single .pdf file. It's attached here for you to look at.

 

Just when I thought I was making progress... lol.   

Attached Files


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#66
Johnny D

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Hi all,

 

I did a bit of digging around and found some info on commercial pad design that *might* be useful to the movers and shakers behind this project. It's out of an on-line catalog, and I had to just grab it as a series of screen shots that I glued together into a single .pdf file. It's attached here for you to look at.

 

Just when I thought I was making progress... lol.   

 

Price ?

 

J~


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#67
Andy Mitchell

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The blurb is just doing some promotion of the overall design of the commercial scales they sell. They don't sell the pads separately.

 

Some interesting stuff in there, though. (1) it gives you actual numbers for how the standard Longacre pad deflects under load, (2) it gives you some comparative numbers for what happens if you substitute 1/2" thick aluminum plate for a better designed pad, and (3) it shows you just what a dramatic effect an off-center load has on scale deflection.

 

That last bit might be a pretty significant cause of non-repeatability during chassis setup procedures. Remember, were talking 800 lb/in springs here, so any sudden 'extra' scale deflections caused by not being exactly back in the same place on each pad between readings might scatter the results a bunch.


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#68
Brandon

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Whitfield Gregg - he's an electronics guy too.

 

More than just a tinkerer if I recall...patent holder and such...

There was a Spec Miata at the June Sprints with the hard top printed circuit board wrapped.

 


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#69
Johnny D

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#70
dstevens

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Hi all,

 

I did a bit of digging around and found some info on commercial pad design that *might* be useful to the movers and shakers behind this project. It's out of an on-line catalog, and I had to just grab it as a series of screen shots that I glued together into a single .pdf file. It's attached here for you to look at.

 

Just when I thought I was making progress... lol.   

Thanks!  That's good reference material.  It also explains some of the cost difference between a Longacre and the import sets from Speedway.  For a maker project we need to use material and tooling for the basic design that are available to a standard fare maker.   The advantage to an open design is that people can take the basic parts and make something that's either better or suits their need better.



#71
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https://www.alibaba....=p     :noidea:


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#72
Johnny D

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300 kilograms = 661.39 pounds


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#73
Bench Racer

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300 kilograms = 661.39 pounds

For each corner. We 1.6er's don't have a corner that comes close to 661 pounds.

 

The real reason for the post is that from China such a set of scales can be had for $300.00 if one buys a $hit load of scales. Granted they do not read results to our needs. Potentially working with them or maybe this bolsters orangecrush and Stevens process. :noidea: 


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#74
OrangeCrush86

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I found 300kg loadcells that would work on alibaba for $10 bucks (but of course no platform)...

 

These would be what you want though, probably the 500 kg model. https://www.alibaba....7115.135.JnuCRE

 

Then add this https://www.alibaba....7115.363.LxlAci



#75
dstevens

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For each corner. We 1.6er's don't have a corner that comes close to 661 pounds.

 

The real reason for the post is that from China such a set of scales can be had for $300.00 if one buys a $hit load of scales. Granted they do not read results to our needs. Potentially working with them or maybe this bolsters orangecrush and Stevens process. :noidea:

Yep, the MOQ is 50 pcs plus freight.  It's too small to get reliable container service and big enough that 50 pcs is going to be a non trivial amount to have air shipped.  That's going to be a common theme for something like this.  Likely a couple hundred plus whatever customs might be.   Where someone like this is good is sourcing parts or pads. I use a place over there that are Aussie and US expats that do sourcing and vendor checking.  I haven't rousted them about this yet as I'm waiting for the first prototypes.

 

The point of open hardware isn't necessarily to sell scales but to provide an open project so that other makers can build them if they like.  There are options to kit things like electronics and perhaps raw parts.  Being able to readily source parts and use assembly/fabrication methods that are common for most garage based makers is a big part of a successful.

 

The first batch of boards cleared production Mon night and shipped.  I may see them by Fri.



#76
dstevens

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35581253306_141ec416a1_z.jpg



#77
dstevens

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On iron with the alpha version software

 

35863169326_103a6a6aa0_z.jpg

 

 

Areas where help would be greatly appreciated...

 

Someone to assist in coding the app, it's in python3, Andrew is a busy guy and could use a hand to shuttle some work to.

 

A reference scale pad design.  That's going to be the lynchpin of the project, getting the pad design light enough, cheap enough and easy enough for a garage guy (or gal) to build to get price arbitrage on low cost import scales.  Even Stonehenge type napkin sketches are appreciated.

 

Main repo  https://github.com/j...open-race-scale  It's his baby, I'm here to hack hardware

 

My fork, pulls from main code, a few different hardware configurations (all using the same parts, mostly fab and form factor differences)

https://github.com/R...open-race-scale  It's a mechanical and electronics fork.

 

For anyone interested I still have some bare boards and now a full BOM and sourcing.  To populate a board it's about $15-20 for a single.  That will get it to the point where you can mount it on a Pi.  Ping me and I'll get you a blank board with the caveat you have to promise to build it and run some code on it.  BOM is in my repo https://github.com/R...n board_BOM.csv



#78
Andy Mitchell

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I can probably help you with pics, measurements of a commercial pad design if you would like.

 

After temporarily trying to revive my home-built scales a while back, I realized that a total re-work was going to be in order to get anything near workable. So I went out and bought a set of used Intercomps. They have cast aluminum pads with heavy ribbing very similar to the longacre design (I couldn't resist opening one up and having a look inside). Probably all kinds of issues with just copying a commercial design, but I'm interested enough in your project to share what I can easily see about them with you.

 

Let me know...


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#79
dstevens

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Thanks.  Anything you think would help is more than welcome.  Dims, designs on how the load cells connect and lever in the casting or anything else mechanical you think would help.  I almost bought a set of used Rebco scales for $300 on ebay a few weeks back to use as a test base.

 

EDIT:  As long as a mechanical method is not patented it's perfectly legal to copy it.  Bolt for bolt, wire per wire.  The scale pad and/or method is not patented.  There could be an issue with using code directly from a closed project but the software side is original open source using open source support methods and mechanisms.   In most cases (and this case specifically) it's perfectly legal to copy the pad design.  The issue would be with hacking the software or using the trademarks of Intercomp, Longacre, etc.  For example if a copyrighted logo was on the pad that was copied there would likely be an issue incorporating the logo.  Basic mechanical design, no problem.

 

If you could plug a dongle into your existing Intercomp set (one battery powered dongle each pad) that would give you wireless capability to your phone/tablet/computer would that be of interest?



#80
BNaumann

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If you could plug a dongle into your existing Intercomp set (one battery powered dongle each pad) that would give you wireless capability to your phone/tablet/computer would that be of interest?


Yes!




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