Rotor Master
 

I've decided to make a stand alone thread for this...

Youtube video with instructions:
https://www.youtube.com/watch?v=0xb_N9yZejc&t=37s
I have been working on my own design for a gauss meter for spec racing rotors. I say spec because it can only measure up to about 1850 gauss. Well, I can make one that will measure up to 4000, but it is a bit more sensitive around zero.

This is based on the ATmega 328p mcu that the Arduino Uno uses. I also am using an external 12 bit adc to get better resolution for the readings, since the arduino has a 10 bit adc. I designed the schematic and the pcb using KiCad, the case is 3d printed and designed in Fusion 360. I am using an arduino sketch for the programming. In theory, someone handy in soldering surface mount components could build one of these based of my designs, which is completely fine.

It works pretty much like the other units on the market. Place the rotor on the holder and spin it to get your readings. I am using 3 sensors to get readings, the middle sensor is the sensor that you should record. The first and the third sensor are there for you to center the rotor. Shim the end of the rotor until you get the 1st sensor and 3rd sensor close in readings at the max value, this will get the middle sensor in the middle of the rotor.

The Rotor Master can be powered off a 2s or 3s lipo or 12v DC power supply. It comes with an XT60 connector on it as a hardware reverse polarity protection. There is no internal circuitry for reverse polarity protection. I probably will add this in the future. Each unit is assembled by hand (mine, lol). I use an accurate bench top dmm to measure each sensor to get the most accurate build that I can. I then calibrate it to a Trinity certified rotor readings.

For anyone who wants to make one themselves, I will provide the schematics, pcb designs, bom, stl, and sketch files needed to make one. I'll get them all into a github repository if there is any interest in it. But making one yourself will require an accurate dmm, an arduino Uno to burn the bootloader on to the bare 328p mcu and then to program it via the rx/tx pins that are broke out.

github repo: https://github.com/trilerian/Rotor-Master

Anyway, here are some pics of the schematic, and pcb design. And then the progress of designing. Enjoy!


https://cimg3.ibsrv.net/gimg/www.rct...8c1a98220a.png
Schematic
https://cimg4.ibsrv.net/gimg/www.rct...044830d968.png
PCB
https://cimg5.ibsrv.net/gimg/www.rct...9df5bfa950.jpg
Proof of concept
https://cimg6.ibsrv.net/gimg/www.rct...40190400cc.jpg
https://cimg7.ibsrv.net/gimg/www.rct...9a7019eec6.jpg
Top view of POF
https://cimg8.ibsrv.net/gimg/www.rct...c2476caa64.jpg
I ordered 20 PCBs!
https://cimg9.ibsrv.net/gimg/www.rct...7675930c89.jpg
Getting ready to build!
https://cimg3.ibsrv.net/gimg/www.rct...b9626640d4.jpg
All the smb stuff soldered on.
https://cimg4.ibsrv.net/gimg/www.rct...c70d5f385b.jpg
And then the through hole components
https://cimg5.ibsrv.net/gimg/www.rct...9f1ecb7e9e.jpg
The finished product!

https://cimg9.ibsrv.net/gimg/www.rct...5efddceb7.jpeg
Fits perfectly in my traveling case
https://cimg0.ibsrv.net/gimg/www.rct...8e83fa43e.jpeg
Padded traveling case
Too tired to test this late. Will play with it tomorrow. Thanks for the quick shipping 👌🏾.

I like the case! I have been looking for an Eva case to use.

i got the case off Amazon after trying to duplicate the exact case the Hobbywing Tunalyser comes with. I couldn’t find that exact case but stumbled across this one.

VERY cool... bummed that stock racing is dead in my area so no longer a need to test my rotors anymore but I can see how this is a great way to check for fade. If stock ever makes a comeback I will certainly build one for sure, great concept!

this is what I like about the hobby....not necessarily winning races, but the fun stuff relating to improving the equipment. I'm too old to be competitive, so I can have a good time building things

this is why I had to support him as he is sharing the info for others to build their own and not just buy from him exclusively. Where else do you see this in our hobby?

Here’s the Amazon link to the case pictyfor anyone that purchases/builds one.

https://www.amazon.com/dp/B07QRFX94D...p_mob_ap_share

Damn, I just bought the Fantom device.

Here is the link to my github repository.
It has:
Bill of Materials
Gerber Files for the PCB - these will work for JLCPCB I don't know about any other manufacturers
STL for the case
Sketch for the programming



https://github.com/trilerian/Rotor-Master


This project would cost somebody appx $165 after taxes and shipping, plus you would need to print the case. But that price is if you need to buy an Arduino Uno, breadboard, and stuff for that.
You will still need a digital multi meter. You would have some extra parts as some of the items are bought in multiples. If you price everything out per part and total it after tax and shipping it is about $35 per unit.

The Fantom is still a great unit!

This is really cool. I'd build one but I dont want to buy whatever you need to flash stuff, unless its super cheap. Though if you flashed it I'd buy it and the PCB and assemble it myself.

Also I'd say you need to be able to measure rotors that get up to about 2200-2500 gauss, as stock is definitly headed there. I think some of the strongest 13mm mod rotors can get to 2000 if not 2200.

But you have a stack of PCBs, are you not planning on selling them at least?

Here are some pics of my unit compared to a Fantom and Magnalyzer.

Using A Trinity certified rotor measured from Trinity at:
1718/-1727


https://cimg6.ibsrv.net/gimg/www.rct...ebea088c3.jpeg
https://cimg7.ibsrv.net/gimg/www.rct...e99c94e6b.jpeg
https://cimg8.ibsrv.net/gimg/www.rct...bc04c1c79.jpeg
https://cimg9.ibsrv.net/gimg/www.rct...d717e2262.jpeg

Yes, I am going to sell these as well. I just made a for sale thread in the for sale forum. I don't really have a website for my stuff as of yet, so it is just here that I am listing them. On request I can make one that will measure up to 4000 gauss. however none of the current products on the market can measure over 1950 at the moment, so that is why I went with the sensors I did. I do have one build for me that will measure 4000 though.

As to a kit so to speak, maybe. I can burn the bootloader onto the mcu and put the sketch on it, but it really needs to be fine tuned after all the components are on the board. There are a lot of variables in my sketch that you change based on the quiescent output voltage of the sensors, the output of the 5v regulator, the "zero" output of the adc, and finally the multiplier to get your final gauss numbers.

What stock rotors get that high? Highest I've heard of is ~1850, I've only seen mod rotors go higher.

I said stock rotors are heading that direction. Reread what I said, you said the same thing as I did more or less.

In what way are they heading in that direction? They've been in the ~1850 upper limit ballpark for years. The rules limit their dimensions and material, which is a pretty big constraint to magnetic strength.

Not all the rotors were the max dimensions a year or so ago when a friend and I did some testing and motor tuning. And materials get refined all the time, so who knows when a stronger magnet will get relased.

My point is that things will eventually progress, and theres mod rotors that already go beyond 2000 strength so a tool that cant measure that is not great. Its nice to track even your mod rotors strength so that motor ever gets hot you can check the rotor strength and see if its hurt. But more importantly having a tool that can do say 2500 accurately now would be useful for years to come giving you a baseline now.

Personally I think a tool with an accurate range of 1000-2500 would be perfect for any 1/10 application right now and for years to come. I applaud trilerian for designing it and basically showing us how to build our own fairly easily. With some hopefully easy tweaks it could be much better. Like I said I want to build one but it'd be much more useful with just a little more range.

The rotors that weren't the max dimension weren't the ones hitting 1850+. Neodymium hasn't had any advancements in a while, so we're not likely to see a sudden jump with a refinement of that process any time soon. Any new material that ends up being stronger won't be legal.

Mod rotors have already been covered as a reason to have a different version, but that's separate to this being useful for stock rotors.

There are a couple of options available for measuring a higher strength rotor. First option is to move the sensors farther away from the rotor. But doing this you have to increase the multiplier you use for your measurement, this reduces resolution in the readings. ie, instead of the number increasing by 1-2, it would increase by 5+.

These units, mine included use a sensor that measures the change of the output of the hall effect sensor. This change is in millivolts. The sensors we use have a sensitivity of 1.3mv/gauss. They have a range of 0.55v-4.50v, with a quiescent output of appx 2.5v. So that is basically a 2000 mv range. 2000/1.3 = 1538 gauss. To get the best resolution, I have the rotor as close to the sensors as I can to achieve the common readings of spec motors.

Another option is to use a sensor with 0.5mv/gauss sensitivity. I do have some of these and have made a unit with them. They will be less accurate, but you can get readings of 4000 gauss using them.

If you can find sensors with a digital output then you can get rid of the AD converter and probably also program the sensors with some filters if needed.

I found a sensor from Texas Instruments that outputs a PWM frequency. Could use that and create interrupts to measure the rising edges to figure out the gauss. Interesting. I will look into this!
Thanks.

Edit: Obviously that is a complete redesign of the entire project, so it may take me a bit to get to.

Edit 2: As to filtering the output of the sensors. I'm glad you brought this up. I was originally planning on putting a low pass filter on the sensor outputs as the datasheet calls that out for the standard design. But after looking at the outputs on my scope I didn't see any difference in the output vs transient noise. This could be a limitation of the scope, considering mine is relatively cheap as far as oscilloscopes go. Regardless in my next design I was going to add a low pass filter to each sensor as well as another decoupling capacitor to each input, but I do think it is just throwing components there that are not really needed.

Case fits beautifully, great find!

Finally life slowed down enough to play with the rotor checker. Another thing for guys to not have to worry about charging a pack to use during testing for this or your motor analyser is this lil power regulator thingy (can’t remember the exact name) Hooks to your power supply and you can set the voltage so tests are repeatable and aren't skewed should lipo voltage drop. Especially when tuning motors. This was about $20 shipped off Amazon. I’ve had this for quite a while so I don’t think I have the link saved. I while search and post it when I have more time later on.
https://cimg4.ibsrv.net/gimg/www.rct...0ac8837c0.jpeg

Duplicate

So comparing this to my Fantom the numbers don’t exactly match but what they both do consistently is give the same readings every time. The lower numbered rotor on my Fantom also showed to be the the lower rotor on this unit. I also like that the connecting plug was provided for me to wire up how I pleased.
https://cimg7.ibsrv.net/gimg/www.rct...ebc651097.jpeg
https://cimg3.ibsrv.net/gimg/www.rct...4cb31dbd2.jpeg
https://cimg7.ibsrv.net/gimg/www.rct...09202a644.jpeg

Just curious, are you checking both plus and minus sides? I only see pics for the minus side. The plus side doesn't have a dash next to it.

I guess I probably should re write the code to make that more apparent. Add a + to the plus side readings.

There are a few more lucky people that have these on the way to them.
Also I have a big order from a distributer I will begin filling next week.

I checked the plus side as well but the pics were all negative it seems. Could also be due to me marking my rotor so I know when I've made one full revolution. The marking is more than likely on the negative side.

Attaching a pdf I made with instructions on how to build and program.

You will need and Arduino
A DMM
Another Arduino to burn the bootloader
The Arduino IDE
PATIENCE!
Soldering skills...

So question... What connectors would people like to see with these?

Deans would be great. Those might be the most popular.

XT60

4mm bullet

Figures... lol

XT60.

I ordered some of the DRV5057A4 sensors and they came in today. I made a quick circuit to test them out. To be honest, the results are less than stellar. So far I can't get the resolution below 8 using the 328p chip. I am going to rewrite the code and try it out with an esp32 to see if the faster clock will provide better resolution.

The HULK, lol.
Purple pcb and green case. Max reading of about 3200 gauss.


https://cimg7.ibsrv.net/gimg/www.rct...521c5b76e.jpeg

That looks really nice.

Did you ever get your car taken care of?