ROS Discussion Group, Tonight! Tuesday, Oct 21 @ 7pm PT

[camp .]

    It's Tuesday again! Whether you're a beginner or an expert, please join us if you're interested in ROS.  :-] 

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Camp

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[camp .]

Tonight! - cp

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[Sergei Grichine]

Here is a follow-up for my demo yesterday (sorry for jerky/lagging video) - the photo album link in notes below leads to a good one.

https://github.com/slgrobotics/robots_bringup/tree/main/Docs/miniPRO

The idea of the project is to understand BLDC motor wheels (Ninebot Segway miniPRO, hoverboards) and create a universal ROS2 "base" (articubot compatible, of course ;-)).

So far, the base works great, moves precisely and has minimal current consumption (12V ~0.5 A idle, close to 1 A normal driving).

SimpleFOC library has means of monitoring currents and speeds. There are no traditional encoders, Hall sensors are used for velocity control feedback. I am not sure that available rotational measurements can be easily used for ROS2 odometry - I might have to use LIDAR odometry package instead.

To view this discussion visit https://groups.google.com/d/msgid/hbrobotics/967190960.5498481.1761095222283%40mail.yahoo.com.

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Best Regards,

-- Sergei

[Chris Albertson]

On Oct 22, 2025, at 11:41 AM, Sergei Grichine <vital...@gmail.com> wrote:

Here is a follow-up for my demo yesterday (sorry for jerky/lagging video) - the photo album link in notes below leads to a good one.

The idea of the project is to understand BLDC motor wheels (Ninebot Segway miniPRO, hoverboards) and create a universal ROS2 "base" (articubot compatible, of course ;-)).

So far, the base works great, moves precisely and has minimal current consumption (12V ~0.5 A idle, close to 1 A normal driving).

SimpleFOC library has means of monitoring currents and speeds. There are no traditional encoders, Hall sensors are used for velocity control feedback. I am not sure that available rotational measurements can be easily used for ROS2 odometry - I might have to use LIDAR odometry package instead.

SimpleFOC.  Does have support of all kinds of encoders, quadrature and serial as well as the built-in Hall type.     You will actually get better performance from the motor if you use a better encoder with at least 1,000 counts per revolution.   

Take a look here: https://docs.simplefoc.com/encoder

I have a few test stands that are just a motor and an encoder.   I use them to test various motors.     I have some larger drone motors and some tiny gimbal motors.    While you can of course get a motor to spin using just the Hall effect sensors, you really can't do good position servoing like you would need with a robot arm or leg.     In the case of an arm or legs, we care about performance at zero or near zero RPM.   Good control at zero RPM is nearly impossible with DC gear motors but pretty easy with SimpleFOC.   

Hall works because you are spinning at near constant RPM and getting only a few “ticks” per rev, but at constant RPM, interpolation works well. Interpolation will not work well with non-uniform speed or near zero speed.   If cost and space are an issue, AS5600 magnetic encoders are very good.  Just attach the magnet to the shaft end with CA glue, and a 1mm air gap works.

Hall sensors were invented so you could drive a BLDC motor with no computer, you just wire the hall to a MOSFET gate and drive the motor with square waves.  But FOC wants better control of the waveform.   

Best practice is to use two encoders, one on the motor and the other after any gear reductions of the wheel or arm.   Then you use a double PID controller.    This will handle mechanical play and flex.  

[Sergei Grichine]

Chris,

"Just attach the magnet to the shaft end with CA glue, and a 1mm air gap works." - would you elaborate on your suggestion, given the actual design of the wheel motor? 

https://youtu.be/QAQ4ugWidlY?t=564

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[Alex Sy]

The wheel has the 3 wires which is the BLDC motor coils and the small connector should have 5 pins (+5V, GND, U, V, W)  The U, V, W are the hall effect output and there is no standard for the wire color code but if you have it's driver you can trace or measure it out. 

Like what Chris said, those have low resolution, ie 4 cyles per rotation since these wheels were meant for hoverboards and are for speed control.   You could glue the diametrical magnet on the center of the outside of the wheel and have the sensor (AS5600, MT6701 or MA730) mounted on a bracket to sense the magnet rotation.  The MA730 will give you very high resolution.  The AS5600 will have a hysteresis jump around the 358 to 2 degree transition and is relatively slow (meant for electronic pots).  It is quite easy to get MT6701 on Ebay already on a board.

Note that although these chips all say they have 12 to 14 bits (4096 to 16384) per revolution, in reality they are all only specified to 1 degree, which may be a problem for accurate arms even if they are sufficiently rigid.  They are perfectly fine for dogs and humanoid legs.  Optical encoders are going to be the most accurate but expensive.

Alex

To view this discussion visit https://groups.google.com/d/msgid/hbrobotics/CA%2BKVXVPJNXi6XzyDjP0AW%3D%2Bn%3DpjWMTv63K0%3D8Ef%3DS1b%3DM2husA%40mail.gmail.com.

[Michael Wimble]

If you want odometry, you could use something I just saw on YouTube from the FRC society, a dead wheel odometry device:

If you don’t mount it to rub on the ground, you might be able to mount it so it rubbed against the inside edge of the wheels.

On Oct 22, 2025, at 6:16 PM, 'Alex Sy' via HomeBrew Robotics Club <hbrob...@googlegroups.com> wrote:

The wheel has the 3 wires which is the BLDC motor coils and the small connector should have 5 pins (+5V, GND, U, V, W)  The U, V, W are the hall effect output and there is no standard for the wire color code but if you have it's driver you can trace or measure it out.  

Like what Chris said, those have low resolution, ie 4 cyles per rotation since these wheels were meant for hoverboards and are for speed control.   You could glue the diametrical magnet on the center of the outside of the wheel and have the sensor (AS5600, MT6701 or MA730) mounted on a bracket to sense the magnet rotation.  The MA730 will give you very high resolution.  The AS5600 will have a hysteresis jump around the 358 to 2 degree transition and is relatively slow (meant for electronic pots).  It is quite easy to get MT6701 on Ebay already on a board.

Note that although these chips all say they have 12 to 14 bits (4096 to 16384) per revolution, in reality they are all only specified to 1 degree, which may be a problem for accurate arms even if they are sufficiently rigid.  They are perfectly fine for dogs and humanoid legs.  Optical encoders are going to be the most accurate but expensive.

Alex

----- Original Message -----

From: Sergei Grichine

To: hbrob...@googlegroups.com

Sent: Wednesday, October 22, 2025 4:36 PM

Subject: Re: [HBRobotics] ROS Discussion Group, Tonight! Tuesday, Oct 21 @ 7pm PT

Chris,

"Just attach the magnet to the shaft end with CA glue, and a 1mm air gap works." - would you elaborate on your suggestion, given the actual design of the wheel motor? 

https://youtu.be/QAQ4ugWidlY?t=564

<image.png>
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On Wed, Oct 22, 2025 at 2:48 PM Chris Albertson <alberts...@gmail.com> wrote:

On Oct 22, 2025, at 11:41 AM, Sergei Grichine <vital...@gmail.com> wrote:

Here is a follow-up for my demo yesterday (sorry for jerky/lagging video) - the photo album link in notes below leads to a good one.

To view this discussion visit https://groups.google.com/d/msgid/hbrobotics/A3FFEE82465D448B95D664B2F436C0DB%40NBF.