85 replies to this topic

[OrangeCrush86]

Hello,

 

I'm making an open source race car scale because I feel like the scales on the market are simply too expensive for the budget racer.

 

I'm looking for feature requests so I can make a roadmap to develop this scale solution.

 

Info:

Target total cost = Less than $250

Interface = Smart Phone app connected to scale controller via bluetooth

Basic features = Total, side to side, front to back, corners, and cross weights

 

If there are any programmers on here I'm looking for collaboration. The repo is here: https://github.com/j...pen-race-scale/

 

What other features would you like to see for a car scale? One example might be a memory feature so that you can compare current weights to a stored data set.

 

Thanks

[Erik Hardy]

What are your plans for the mechanical side of things? 

[OrangeCrush86]

What are your plans for the mechanical side of things? 

 

I will publish a cad drawing for the load cell plates and a bill of materials. So far I have found some 1k lbs load cells for $50 each which gives a 4k lb capacity. For now the plan on the electrical side is to use a Raspberry Pi 3 which gives a lot of options.

[OrangeCrush86]

If there is an Admin that can move this to a better spot I would appreciate it, I think this might be the wrong area... Maybe Data Acquisition would fit better. Thanks.

[Johnny D]

To me it's fine. I like the idea. Need scales for a set up.

I haven't moved a thread before either.   but could if I wanted to.

 

FYI, I normally hit the "view new content" button upper right. I/we won't miss your updates.

J~

[Johnny D]

Sorry I'm a mechanical guy so I have to ask...why the phone and all the software ??

 

Have your load cells display the weight, end of story, for $200 I'll walk around to each corner.

 

Now if your were doing 3d (maybe gps) alignment camber, caster, toe, maybe I can see why you'd need the software.

 

J~

[luvin_the_rings]

design in some leveling feet so we don't have to buy a separate scale stand. 

[Steve Scheifler]

Scales are certainly not cheap but they are relatively low volume so I don't begrudge them the margin, much. But I'll be very impressed if you can create a sufficiently accurate DIY set for your target cost. What are you budgeting for the pads? Perhaps by negotiating a group-buy to make multiple sets it would be possible. Don't underestimate the importance of making those flat and rigid.

[OrangeCrush86]

Sorry I'm a mechanical guy so I have to ask...why the phone and all the software ??

 

Have your load cells display the weight, end of story, for $200 I'll walk around to each corner.

 

Now if your were doing 3d (maybe gps) alignment camber, caster, toe, maybe I can see why you'd need the software.

 

J~

 

A few reasons.

1. Besides the fact that I like to make software, the main reason is so that I can sit in the car while taking the weights. My current Proform scale is kind of annoying to look out the window and try to read the tiny display.

2. Other than being able to do extra stuff with the data, like store setups, it's actually cheaper to send the scale data to a phone. It essentially removes the cost of LCD displays.

3. I plan on having a local display option later for people that don't want a phone app, but again, it's extra development time and cost.

[Johnny D]

Cool, I have a machine shop and can do the leveling base plate etc for the load cells. Downside is I'm in CA. Get your software figured out I'll do some prototypes for a complete set in return.

J~

[Brandon]

I'd claim the reason for the stands is just that - scales scale, stands stand.

 

Divorcing the two means you can ensure absolute precision on the one piece without impacting the other.

Or flip it around: imprecision on one doesn't impact the one where precision is paramount.

 

design in some leveling feet so we don't have to buy a separate scale stand. 

[luvin_the_rings]

I'd claim the reason for the stands is just that - scales scale, stands stand.

 

Divorcing the two means you can ensure absolute precision on the one piece without impacting the other.

Or flip it around: imprecision on one doesn't impact the one where precision is paramount.

 I'd claim that a well designed product wont affect the precision of either. 

[OrangeCrush86]

To be clear. This project is mostly focused on making a weighing solution available. Not supplying any parts (unless we had a few people in which case we could split the cost to have some PCBs manufactured).

 

In other words the software and plans are free. You buy a Raspberry Pi3 and get a PCB (or build your own) based on the schematics. Then you order some load cells that meet your application from Amazon and build the mounting plates yourself. Any mounting plate plans I put up will most likely be whatever is simplest to manufacture in a garage.

[Brandon]

To be clear. This project is mostly focused on making a weighing solution available. Not supplying any parts (unless we had a few people in which case we could split the cost to have some PCBs manufactured).

 

In other words the software and plans are free. You buy a Raspberry Pi3 and get a PCB (or build your own) based on the schematics. Then you order some load cells that meet your application from Amazon and build the mounting plates yourself. Any mounting plate plans I put up will most likely be whatever is simplest to manufacture in a garage.

 

So no CNC'ed aluminum plates are in your manufacturing future?

[Johnny D]

So no CNC'ed aluminum plates are in your manufacturing future?

 

I can do them, have to design to the load cell and figure cost.

 

Need a PCB Manufacturer, BOM, I could find one around here (silicon valley)

 

Parts List

Load Cell P/n ?

Raspberry Pi3 p/n ?

Leveling feet P/n ?         https://www.mcmaster...g-feet/=17ytflb

 

Who interested in some of this ^ (PCB, plates) or a full package?. I understand you'll want to see it 1st.

Just askin

 

J~

[Bench Racer]

Blue skying/Ingenious thoughts thought's always appreciated by me.

 

Electronics   $250.00

Load Cells    $200.00

Leveling feet $108.00 16 required  (to reduce this cost, use Carriage bolts)

 

Sub Total     $558.00 Anyone see where this is headed?

 

My frugal system is approx. $1,000.00 for scales plus $50.00 for adjustable wood stands for a total of say $1,100.00. The cords are long enough the scale readout box is in the car with me. Get a buddy, each chip in  50% each and be done. I have viewed scales from back in the day which had adjusting screws within the scale. I use a $27.00 water leveling tool which is not included in above cost.

[luvin_the_rings]

I use a $27.00 water leveling tool which is not included in above cost. 

 

 

I made myself one of these too.  Best thing ever. 

 

2 plastic graduated cylinders, some plastic tubing and some electrical tape and ultra black. 

 

I love how the difference in the heights of the water is actually twice the distance that the scale is off true, so its a very sensitive way of leveling the scales. 

 

-Z

[Bench Racer]

Also made my first liquid level. Bought my second 8-10 years ago for $27.00, today it's $29.99.

http://www.speedwaym...-Hose,2702.html

[Johnny D]

So here's what I'm thinking and some more numbers..

4 plates 1' wide x 2', so you can roll off and on. Need to machine a pocket for the load cell ?

If I got an Aluminum plate 12" wide and 6ft long and 3/8" think (kind of thin) it's 166.70, 3 pcs, 166.70 / 3 = 55.56 a pc

So about $222, Plus shipping / tax, I haven't touched them yet or shipped it to you.

 

https://www.mcmaster...sheets/=17yuh4g

 

They also have 1'x2' (whatever thick) if you don't want to cut it and order it yourself. For the DIY'r

 

It's adding up pretty quick.

J~

[OrangeCrush86]

You guys are going a little steep.

 

I bought one of these loadcells for a test: https://www.amazon.c...1_O0gozb0RDP7V8

My weigh plates are prototyped in ply wood for now. Basically I'm imagining 1/4 steel plate approximately 12"x12" or similar. 1/4 carbon steel plate is about $10 a square foot.

 

So I get this so far...

4x 1k loadcells = $200 - https://www.amazon.c...1_O0gozb0RDP7V8

1x RPi3 = $36 - https://www.amazon.c...1_L9gozbNQBY5F4 (could be swapped for RPi Zero W for 10 dollars less)

4x Loadcell ADCs = $8 - https://www.amazon.c...1_z.gozbGZ390B2

1x PCB = ~$12 - Prototype boards in low quantity can be ordered in minimum of 3 units @ approximately $37 dollars (Optional cost, you could wire the electronics with no board)

8x steel plates = $85 - any local fab shop should have something like this; no leveling mechanism

Misc hardware = $20 - bolts, etc

 

Each set of plates requires 3 holes to be drilled for mounting load cells that can be done yourself.

 

Total cost is $361.

 

That is bare minimum, but we could actually work on this platform and extend functionality etc. I don't know if the other scale companies even have a phone app wireless interface or ability to store measurements etc, but they definitely are not on their entry level products. Honestly with a little more work and another $100 in electronics we could even have wireless battery powered pads.

 

If anyone has an idea of how to get the cost of the plates lower that would be huge since electronics are already dirt cheap and load cells probably won't be easy to get cheaper.

 

In the end this is just an experiment for me. It's entirely possible that we can't beat the manufacturers that can keep costs low with mass production.