CG Scale geek way - RC Groups
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Jul 05, 2017, 11:47 AM
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CG Scale geek way


Hi

After seen those nice cg scales that showed recently for sale, the other one in this forum and the pierre rondel post about how the obtain the cg with two scales i feel that i need to get one... in a low budget mode but keeping the geek spirit.

I think in design one using weight cells and an arduino and looking for info on those cells i found a nice project on a github repository https://github.com/olkal/CG_scale You can fin in this repo a bom file with all components listed, schematics and stl files.... all you will need to build one. The owner its a nice person he even modify the supports stl files to fit my f5j glider... Thanks Olav!!! because it was originally made for narrow f3f/f3b fuselages.

So im going to do a build thread on building one of those gadgets.

I have the 3d files printed and hope to get my electronics this week
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Jul 05, 2017, 04:45 PM
Registered User
I started buying stuff for this as well. Takes a few weeks to get stuff from China here in the states.

It looks pretty straightforward. Do you really need another Arduino pro mini for the LCD?

Why not just go with a 4 wire display?

Makes no difference but it saves a lot of soldering.
Jul 05, 2017, 07:57 PM
VHO
VHO
glider misguider
Looks like a great project. Will follow and copy with interest.

How much wider is the F5J /F3J frame, and is it in the files?
Jul 06, 2017, 09:39 AM
1 revolution and throw!
would it be suitable for smaller planes aswell? f3k?
Jul 06, 2017, 11:25 AM
Registered User
Quote:
Originally Posted by VHO
Looks like a great project. Will follow and copy with interest.

How much wider is the F5J /F3J frame, and is it in the files?
I will upload later a photo comparing the two structures, its a bit wider but more height


Quote:
Originally Posted by krikkens
would it be suitable for smaller planes aswell? f3k?
Of course, the original supports sizes fits ok my stream f3k, if im going to use exclusive on f3k planes i will use cells weight of lower range... for example 1kg or less



Quote:
Originally Posted by Bmwjoon
I started buying stuff for this as well. Takes a few weeks to get stuff from China here in the states.

It looks pretty straightforward. Do you really need another Arduino pro mini for the LCD?

Why not just go with a 4 wire display?

Makes no difference but it saves a lot of soldering.
Im not the author of the project so i dont know the main reason for that... in my opinion you can implement the display in another way... even you can replace the main arduino with an esp8266 board and use no lcd, instead program an internal webserver and ap so you will connect to the board using cellphone wifi and view the data on the phone. Use what you want for display
Jul 06, 2017, 01:15 PM
Registered User
Here its a photo of the two supports, smaller one its the original from repo and the other its the other that the repo owner modify to fit my xplorer 3f 5j.

https://github.com/olkal/CG_scale/issues/1
Jul 07, 2017, 06:56 AM
1 revolution and throw!
are these cells not accurate enough?

i would like to build it and use it for 200-2000gram models (f3k & f5j)
Jul 07, 2017, 01:45 PM
Registered User
Quote:
Originally Posted by krikkens
are these cells not accurate enough?

i would like to build it and use it for 200-2000gram models (f3k & f5j)
Yep no problem with the cells, they should cover the range you need, i did not understand you correctly, i thought that you will only want to use them for f3k so i made that comment. When you calibrate the cell have to use a know weight object in the max range of the cell since my comment.

Im also bulding mine to cover f3k, f3f and f5j so i have a max weight a little bigger than you.
Jul 09, 2017, 02:25 AM
a.k.a Frank Campbell
I built a CG Scale last year using 3 load cells

https://www.rcgroups.com/forums/show...9&postcount=42

The full thread is here

https://www.rcgroups.com/forums/show...5-Measuring-CG

It uses an Arduino, 3 load cells, 3 amplifiers, a 4x24 display and a 4x4 keypad.

The first version is somewhat crude but very effective. I am working on a much more refined version with the aim of making construction simple and cheap plus giving something better looking.

I considered versions using both 1 and 2 load cells but decided on 3 simply because the resulting platform is more stable.

I think any device that uses load cells and a cradle of some sort is a much better way of measuring CG and I use mine all the time.

Frank

Edit. It also gives lateral balance reading
Last edited by VintageFan; Jul 09, 2017 at 04:01 AM.
Jul 09, 2017, 07:27 AM
Registered User
Brett82's Avatar
I've received some of my parts and will start the printing this week.

I've gone for 2x 5kg load cells. Might be over kill for my F3F models but I thought that way I could print some brackets that would allow me to put a wider fuzz on with a heavier scale model if needed in the future.

Im also using a slightly different arduino board. Just the one will be fine for both cells and the lcd.

Looking forward to seeing more of your progress.
Jul 09, 2017, 04:44 PM
Registered User
Im still waiting to receive the cells, and go to buy some screws and nuts.

i made the lcd part, i only used a pot in the lcd part and also modify two pins wiring, pinks A and K from lcd are used to power the backlight, K goes to ground and no resistance. I think its easier to have the pot and also you can use to adjust contrast.
Jul 09, 2017, 06:00 PM
Registered User
Agreed, way easier to use the pot for the LCD.

5kg load cells should be fine.

Would make it easier for B / F models to adjust your ballast.
Jul 10, 2017, 02:15 AM
Registered User
Brett82's Avatar
Awesome, looks good. I've gone for an lcd with a built in pot on the back of it. It was only 2 and thought it would make it a bit easier.
Jul 10, 2017, 04:02 AM
doo
doo
Registered User
doo's Avatar
Very cool guys. This looks like a fun project. I have no previous experience with Arduino, so hopefully I can get some help along the way.

Frank, I like your design with the 3 load cells for lateral balance, larger display and keypad.
Once you get your design finalized, would you be willing to share your Aurduino programming, and perhaps a wiring diagram?

Thanks.
Jul 10, 2017, 10:07 AM
a.k.a Frank Campbell
Quote:
Originally Posted by doo
Very cool guys. This looks like a fun project. I have no previous experience with Arduino, so hopefully I can get some help along the way.

Frank, I like your design with the 3 load cells for lateral balance, larger display and keypad.
Once you get your design finalized, would you be willing to share your Aurduino programming, and perhaps a wiring diagram?

Thanks.
I'm working on this now. I plan to publish mechanical drawings, wiring diagram and Arduino code.

I'm trying to find materials that are easy to get and cheap. Making it all wood is one option but requires some precision woodworking

I find the 3D printer approach in this thread and the one kcaldwel started very interesting but not something I want to try at the moment

I don't want to hijack this thread so when I am ready to publish what I have I'll start a new thread.

Frank


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