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tonym

F3x or F5x CofG scale

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tonym

I recently bought a 3D printer and while looking for interesting model related things to print I came across various CG scale things on RCGroups eventually finding mention of Olav Kallhovd's F3x CG Scale. I like a challenge, I play with Raspberry Pis but have never used Arduinos before so have started to build this scale for my F5J models.

I also found Mike Shellim's blog on his build of the scale - I'm hoping Mike @rc-soar will chime in on this thread with answers to my(our) questions and add any advice or changes that he has made, or would make to the scale. I have printed the wider F5J supports

My first question is: I've bought the 1602 display with an i2c module, does that mean I don't need a second Arduino to power the display?
Second, and related question: will I need a deeper box for the display unit with just the i2c attached? Mike, could you perhaps post your adjusted .stl in this thread? (My brain turned to mush trying to do the alteration in FreeCAD, TinkerCAD is my limit at the moment 🙂 )

The parts, still a few bits to print plus wire to connect things together
parts.thumb.jpg.c6078e88ed0fd6821607da73ce922f29.jpg

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cirrusRC

Nice Tony.  I've been meaning to order the parts for this for a while now.  I don't have a 3d printer yet though.

Your a lot further a long than me.  Be interesting to see which load cells and amplifiers you got?

I was following this thread on rcg https://www.rcgroups.com/forums/showthread.php?2917114-CG-Scale-geek-way

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tonym

I bought a 1kg and a 2kg load cell(s) off ebay - HX711-AD load cells  - no idea if they're going to work but I thought 3kg all up is more than I'll need. These are the most expensive bits of the build, think I could have got cheaper from China but thought the wait to get them would be too long.

Kompatibeler Microcontroller Mini ATmega328 16MHz Blue 5v - £3.83 each - madness! Seem OK but we'll see when it's all together and hopefully working.

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AJH

"does that mean I don't need a second Arduino to power the display?"
Yes, only one Arduino is required.

"Second, and related question: will I need a deeper box for the display unit with just the i2c attached?"
I did

" Mike, could you perhaps post your adjusted .stl in this thread? (My brain turned to mush trying to do the alteration in FreeCAD"
I simply stretched the depth of the original file in the slicer, wastes a little material, but saved my brain from turning to mush and takes seconds to do.

 

AJH

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tonym

Thanks AJH - excellent idea about stretching the box in the slicer, might see if I can inject a load of layers in the gcode instead of a stretch 😮

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rc-soar

Stumbled on this thread a bit late, but looks like you're home and dry Tony, thanks to top advice here. In the meantime I've edited the review to clarify the different requirements of the I2C and non-I2C LCD panels.

Good luck with the build 🙂

 

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tonym

Been struggling for several  hours to get something to come up on the LCD - find out both Arduinos are 3.3v units not 5. Hopefully the seller can supply 5v versions but for now the cg scale project gets put to one side and I can play with my new RPi 4 which I hope will be a good 4K media player.

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tonym

It's finished and it works.

As the LCD likes 5v I just power the display with a 2S LiPo with a 5v regulator - they hang outside along with the LCD, no 3D printed box for LCD yet. Haven't heard from the seller of Arduinos yet, worked around the voltage problem with the external LiPo.
User error(s):
Don't follow wiring for load cell amplifiers from github diagram, follow the diagram for actual amplifiers bought so wires are in the right place - worked then.
Get front and rear load cells wired in the right order - trying to calibrate them when they're the wrong way round causes head scratching - altering sketch solved that.
Ensure wires from load cell are properly soldered after taking them out and putting them in the right place - stops weights fluctuating when configuring.

Apart from the above everything went swimmingly 🙂

Just noticed I've made a poor job of seating the load cells, got a distinct list to starb'rd - soon fixed, might need recalibrating though.

cg-scale.thumb.jpg.8b5e8b2fd90e5ba16f9edf02024939a4.jpg

 

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cirrusRC

nice work Tony

  • so you used 2 different load cells?  1kg and 2kg?   Makes no difference once calibrated and calcs done?
  • what did you use for the leading edge stop?  They look too shiny for nails :)
  • Is is too large for DLG use?   Sounds like the flaps will rest on the back supports?   Think there is a smaller version dedicated for DLG right?

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tonym

Load cell seat fettled, trimmed 'channel' side rather than ovaled the screw holes, I found it easier. Checked calibration, changed by 1g, I'm using a 500g test weight.

Front cell_1_calfactor = 942.0
Rear cell_2_calfactor = 2292.0

I put the 2kg load cell at the front, others seem to put the 'bigger' cell at the back. A model always seems to me to be front heavy, obviously it balances, but nearer the leading edge than the trailing usually(?).

The stops are 3mm piano wire.
My XXLite doesn't fit, misses the rear pads 🙂  - 'normal' wing (Steigeisen) fits OK, though it is the flaperons resting on the pads, will it matter? There is mention of a DLG version on RCGroups somewhere, and in the geek cg scale thread people mention using this scale with their DLGs.

 

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cirrusRC

Thanks.   Still don't understand why different sized load cells are used.   I figured 2x1 or 2x2.

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tonym

Sorry I didn't really answer that David.

I can't find any reason to have differing sized load cells either. I think basically you decide what the heaviest model you're likely to put on the scales, add another kilo(?) My maximum weight will be 3kg, possibly 2.5kg for a more accurate measurement? My thinking on going for the 1 & 2kg cells is that they're possibly going to have a higher resolution (is that the right term?) than 2 and 3kg cells, not by much, or anything significant I would guess. Also I very much doubt I'll ever have gliders over 2kg that I'd bother to want to get the CofG down to the millimetre.

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GeoffN

I've used 5kg cells .They work ok as far as i can see.Repeatable results down to a mm. Cheap as well.

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