Tarot 4108 380KV

Hey there, I am just getting started, and I would like to know if it even makes sense to start testing with a Tarot 4108 380KV BLDC? I know it is not what this board is designed to handle, but I need to order proper motors and would like to just dive into it an test so code now…obviously without breaking anything!

These are the motor specs, while running it on a 15V 15A psup…
phase_inductance = 2.77221915894188e-05 (float)
phase_resistance = 0.2512487769126892 (float)
torque_constant = 0.021763157099485397 (float)
I could use a super low amp psup with flexible voltage output, or a 5V switching psup with 20A

Should I give it a try, or stay patient… :slight_smile:

The motor is fine. And it might be a bit too much powerful.
A PSU with programmable current limit is what you need .

Yes, you can use a motor like that with the SimpleFOC shield.
What you have to do is limit the current draw by limiting the voltage by changing these two parameters:

float voltage_limit = 1;
motor.voltage_sensor_align = voltageLimit/2;
motor.voltage_limit = voltageLimit;

Start with a really low voltage, maybe even lower than 1V and go from there. I like to have my sensor align voltage half of my voltage limit for closed loop control, but it doesn’t have to be that way.

Thanks for the reply guys…I will give it a try then!
Just getting started over here, and dont want to break stuff right away!

Is there a thread where best practice in motor choice discussion is going on?
It would definetely want to go ahead and buy some which are more suited for this scenario!

Hey David, now I realized I know you from that Dagor Brushless Controller that you are developing…are you over on Discord too?
Send me a link… :slight_smile:

I use discord, but I don’t know how to share my profile haha.
I don’t have a channel for the board. Maybe this may be of interest for some people, not sure.

Just add me, might be nice if there is something off topic to exchange… :slight_smile:

Mickey666Maus#3529

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I made this one: https://community.simplefoc.com/t/motor-and-driver-database-as-website-feature/335/5

You could submit new motors using this form:


And browse existing motors here:

Same for drivers:


I haven’t added many yet, but please, feel free to add yours in order to help the other people.

For choosing motors, normally I guess the application should guide the choice of motor, and that in turn the driver, but for the specific purpose of experimenting with SimpleFOC, currently I feel high-Ohm winding motors work best.
This is because current limiting is work in progress in SimpleFOC, and until it works well you have to run low-Ohm motors at very low voltages to ensure you don’t burn things through too much current. And running the motor at such a low voltage limits its performance. In particular, a 6S motor probably has 0.1Ω resistance or even less, and this means you’ll want something like 0.3V or even less to be safe, depending on your driver. That’s really low for a motor designed to run at 22.2V… correspondingly you will get almost no torque and only low speeds.
On the other hand, a 10Ω motor at 3S can be run by most drivers with current flowing continuously, and even at 22V it would only be 2.2A, which many drivers can handle continuously without special cooling. So this type of motor will be unproblematic to run and test, and you won’t destroy your drivers and MCUs if you accidentally run it at full voltage through a software bug.

Such motors are typically sold as “Gimbal Motors” or “Torque Motors”. Depending on your budget you can find smaller, no-name ones on AliExpress for as low as 5 EUR, or really amazing big expensive ones for 500 EUR from the USA or Germany. Some nice models are the Emax ones, which are not so expensive, or the iPower series which already integrate the AS5048 absolute position magnetic encoder, saving you the trouble of shimming it up yourself.

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Some other thoughts:

380KV at 20V is 7600RPM (max speed). That is probably faster than you’ll be able to do with FOC commutation, depending on your sensors and MCU…
If you want to go fast, pay attention to sensors and MCU to make sure you have the maximum FOC iteration speed. If you don’t need to go so fast, pick a motor with lower KV…

If you have a good method for mounting a magnet to the back of such a motor, please let me know! I have been puzzling about how to do this for some time now…

Hey there, thanks for the input…I am just getting started here, so there is still a bit of a learning curve for me, your information is very helpful!
I actually bought the motor for a robotic application, and I kind of just went with a semi random one, among those that were commonly used by some projects that used BLDCs for robotic applications.

At the moment I am using a pretty high reduction ratio gearbox on top of that motor and am using the ODrive to run it…but for the gripper that I am about to build, I am looking for way less torque. So I can also run a lesser reduction ratio, and don’t need to spin those motors as fast to get the desired speed of motion. That is why I was thinking of a SimpleFOC solution?
I wanted to test the board and was a bit afraid to break it…these motors can draw a lot of current when loaded!

I am currently using a CUI AMT102 capacitive encoder but already ordered some AS5047P-TS_EK_AB encoders, one for for absolute position on the motor shaft and one for the gearbox output to keep track of turns…so once they arrive, I will look into a good way of attaching the magnets.

Thanks for the help, and if there is a particular motor you would recommend to get started, please paste the link!
I will I take your airtable as a starting point and will be looking for Emax and iPower branded ones first…
The idea of having an encoder already build in, would also be a nice addon, depending on the price… :slight_smile:

That tarot is going to work well enough, just make sure you set the appropiate voltage limits and start with SMALL numbers.

I have to say I’m finding the Gimbal motors quite similar in terms of performance, its more about the form-factor. Some of them are quite flat, that might be good for a gripper, and others more narrow and tall.
I find it quite fiddly to attach the magnets for the magnetic encoders. A hollow shaft means I can just 3D-print a magnet holder like this:
image image
Where the pin sticks in the shaft and I press the magnet in from the other side. These work well enough provided the motor does not get hot enough to deform the plastic :wink:
The AS5047P-TS_EK_AB has a selection jumper soldered on the board which sticks out in the wrong direction :frowning: It’s really unfortunate they soldered that one on, the AS5058 versions don’t have it. I recently ordered a couple of AS5047P-TS_EK_ABs, and I’ll have to de-solder or saw off that jumper to mount them well.
That’s why the iPower motors, despite costing a little more, are (IMHO) quite good for prototyping as they have the encoders conveniently integrated. They have the AS5048A (SPI) which is the one you want anyway.

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There’s one huge difference though. Gimbal motors usually have a high phase resistance (around 10 ohms) so you would need let’s say 20V to draw 2 Amps, with drone motor’s you could probably do the same with less than 5V and a software voltage limit.

@runger Thanks for your opinion, actually this is what I am looking for to get started. Just gathering some opinions on best practice scenarios… :slight_smile:
Its quiet tempting to use the build in encoder for the motor shaft, so I would only have to worry about the other one on the output. I realized the weird jumper, but am planning to just solder it to the desired position, there are some connections to be soldered on anyways, so its kinda OK. Although the design is kind of odd!

@David_Gonzalez Thanks for the clarification…am I right assuming that a gimbal motor will produce less torque at the same volts? And a low KV rated motor will be more sensitive to a voltage change and spin slower at the same voltage, but will also produce more torque at the same volts and draw more amps?

This is my current gearbox for the Tarot 4108, if you are interested! It is a 40:1 Cyclodial Reducer…
I am planing to move the shaft and mount the new encoder to the back of the design.

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Btw, found these ones…what are your thoughts?

AliExpress

also AliExpress

The two motors on the Airtable are out of stock…you could also just throw in a link from Ali Express, or any other site! The motors I found are having a resistance of 3.5 and 7.5 Ohm…

There is a smaller one that I found which is rated 12 Ohm

12 Ohm Gimbal

I would like to get an overview of which motor types would work, so I can estimate where on my robotic application I can deploy them. It always kind of boils down to available space and weight vs torque and speed obviously!

Oh, and yes @runger good point mentioning the problems of mounting the encoder on a 3D printed part, while exposed to a lot of heat…

:smiley: it looks like we have similar ideas!

At the moment I’m working more on smaller robots than the one that needs the cycloid… so that design is on hold for the moment.

Note that on the output side you might be able to get away with a cheaper encoder like the AS5600 - you might not need the 14 bits resolution when you’re not measuring at the motor, since the sensitivity will already be x40…

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I will try to add all the motors I have bought so far to the air table tonight… Any of the 3 links you sent should work just fine…

Another coincidence: 4 of the GB4008 motors arrived in my mailbox from AliExpress today.
I like the price on those :slight_smile: I will see if I can try them out for you tonight and post a video.