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Picture of Brushless Motor Thrust Stand

Back in the time when I was building my Arduino based Ludwik Drone I faced a problem of choosing proper motors and propellers. I didn't know anything about drones at that time so I had to trust motor manufacturer and the datasheet of a motor those are most likely to be a good source of information but what if you want to combine different motors and propellers together? You still need to know the thrust of the motor and propeller, golden rule for drones is to have at least 2 times bigger thrust than weight of your drone (it depends on what type of drone you want to build this rules doesn't work for racing/acrobat drones and some other). I thought that there must be a device for measuring thrust of a motor, I found some online but those were really expensive so an obvious decision for me wast to design my own! I found some time during my internship at CIT (I was working on airfoil design and testing for a VTOL drone here, that was very cool!) to design a PCB without prototyping and any of the parts, just online datasheets. Surprisingly PCB work just fine! If you want to test your motors keep reading!

Step 1: Parts

Picture of Parts

We will need components that are listed below, check out values of them on the schematic:

edmitchell5 months ago
I see the load cell is limited to 1kg max. What do I need to
do to increase this. I see they have a
20kg version. I also need to bump the current max up to 70a. Is this

Thanks \Ed
Jacat8 months ago
Hey, nice job.
Where did you get HX711.h library from?
kilroy078 months ago
Okay, so I've looked everywhere (I even installed KiCAD) and I do not see the values for R3 and R4. can you list those please?

Also, your connection for the ESC is incorrect. It should be Signal, 5v, ground.
Should be an easy modification to the board's layout.

kilroy079 months ago
Do you have a more detailed parts list? (You mention "Some SMD resistors" & "Some ceramic capacitors, Choke") do you have values and quantities?) Or are the values silk-screened onto the board?

The only other suggestion I would make is there seems to be plenty of room, how about using full sized components rather than SMD which are a pain to solder (at least for me!) LOL

Other than those two points great project (You've got my vote.) I fly mostly fixed wing and this will be a great winter project!

I JUST placed my order for the PCB boards.

Oh, one more quick question, it seems amperage detection is limited by the module selected, is that correct? (Some of my bigger motors can draw 40+ amps...) I will most likely upgrade the module to be able to measure more amps.

Nikus (author)  kilroy079 months ago
Those resistor's package is 1206 and you can find values in the schematic. Choke and capacitors values also can be found in the schematic.
I actually prefer to solder SMD (1206 are not that small) it's faster for me to solder and those are less expensive too. Thank you very much I am happy that you like it! Thanks for the vote :)
Think about using different tensometric beam/strain gauge, I used one that can measure up to 5kg, there are also 10kg and 20kg version.
Yes module that I used can measure up to 20A, for me that's enough. 40A is a lot! If this module is controlled just like the one I used, sure you can easily replace it.
Good luck with the project.
Have a nice day!
kilroy07 Nikus8 months ago
Okay, so I've looked everywhere (I even installed KiCAD) and I do not see the values for R3 and R4. zcan you list those please?
barry99 months ago
Would love to build this but can't open Thruststand.sch. What program was it generated on? I have Eagle 9.2.2 free and it won't read it
Nikus (author)  barry99 months ago
It was designed in KiCad
barry9 Nikus9 months ago
Thanks for the prompt reply, will get a copy and decode it. Regards
barry9 barry99 months ago
Hi got KiCAD 5.0.2. Ran Eeschema and it recognised the file BUT it threw a wobbly at the symbol Library and "converted" them to the new format. Result I can read the labelling on the Arduino, power supply and LCD but no numbers for the pins, just a square with 2 ? on it. Kinda frustrating as I really want to try and build this handy gadget. Any comments, suggestions etc would be really appreciated.
barry9 barry99 months ago
Hi attached a picture of what Eeshema does to your schematic. I am guessing that there is a difference in the libraries. I get all sorts of doom messages about mapping items to new library when I open the file
EEschema screen under Kicad 5.0.2.jpg
Nikus (author)  barry99 months ago
So you are using Eeshema, try with kicad or ask someone for help that know how to conevert kicad schematic to something else. I never used eeshema so I wouldn't help a lot here.
barry9 Nikus8 months ago
Hi. Tried KiCAD 4.0.7 Same result, lots of squares with question marks in them and the same error messages on loading. Looks like this is going on the back burner while I give it three coats of thinking. Thanks for trying.
Nikus (author)  barry99 months ago
You probably miss a library, but if I remember correctly I didn't use any custom libraries. Can you add a screen of what you see in the kicad?
barry9 Nikus9 months ago
Hi. Tried to open the file in KiCAD but it keeps using Eeschema. I assume that this is the module within KiCAD that is used for Schematic editing. I will try installing KiCAD 4 and see if that will read it.
MadScott9 months ago
came over from Hackaday:

This is an absolutely great build given that it’s all self-designed PCB and hand-soldered SMD – great work!

Having worked with load cells for a very long time, I’m curious how you calibrated the load cell/thrust output (maybe I missed something) – it looks like you're just trusting the data sheet for information (the code has a very simple calibration factor in it). If it’s not calibrated, you’ll just have a relative value for thrust.

The simplest “good enough” calibration for this rig would be to orient the beam horizontally with the motor mount facing upward and then hang a series of known weights on it from the center of the motor mount. Unless gravity's gone wonky you'll get pretty good calibration values.

Again, great work - hope to see many more great projects in future.
Nikus (author)  MadScott9 months ago
Thanks! Cool to know that my project is on Hackaday! Of course, I calibrated it before using it, there is a sketch in the examples of a library for this module that explain how to do the calibration. It's basically as simple as you said. The program calculates some kind of an offset that is a constant value that you have to add to your code. I checked if it can measure weight of few objects and it's really precise. Thank you!
Phil_S9 months ago
Looks like fun, but nicely done. Beats starting a big old diesel engine in a bench vice. Fingers out of the way before the engine fires. The brushless motors have transformed all aspects of aero-modelling. I love to see these drones operating - huge future potential
Nikus (author)  Phil_S9 months ago
Jacat9 months ago
Very nice job.
I was not able to find the top of the beam, the motor mount.
Is that available?
Nikus (author)  Jacat9 months ago
Thanks, looks like I uploaded old PCB case design instead of motor mount, thanks for pointing out! You can find it in step 4
Amardes9 months ago
That's awesome!!!
My vote goes for you...
Nikus (author)  Amardes9 months ago
Thank you very much!
florindgis9 months ago
Nice work, well done!!!
Hope to see more from you in the future.
Nikus (author)  florindgis9 months ago
Thanks, subscribe to my channel to don't miss it :)