[TriEmbed] Designing a brushless motor controller during the chip shortage

[Carl Nobile]

Charly,

There are a few solutions to the controller problem. I designed an analog
PWM circuit using op-amps and comparators that works great. You would also
need an H-Bridge you would then need just one MCU board to control the PWM
circuits then then control the H-Bridge circuits.
My design is at: https://github.com/cnobile2012/VoltageControlledPWM
My motors are fairly low current and voltage so the H-Bridges I'm using
won't work for you, however MPJA.com has one in the link below, that will
handle higher currents.
https://www.mpja.com/Dual-H-Bridge-DC-Motor-Driver/productinfo/35567+MP/
It will handle two motors and is only $22.95 ea. They give full docs on
their site.
My PWM board shou interface with it fine.

~Carl

On Sun, Oct 3, 2021 at 11:16 PM Charles West via TriEmbed <
triembed at triembed.org> wrote:

> Hello all!
>
> For the past 5 years or so, I've been working on a open source low cost
> sidewalk delivery robot.  The current draft (prototype picture:
> http://goodbot.ai/lib/exe/fetch.php?media=mk3draft1.jpg) has 4 hoverboard
> style motors in a skid steer arrangement.  Each robot will need 4 motor
> controllers, which is one the big cost drivers right now (even prior to the
> covid shortage, the controller cost more than the motors).
>
> My last stab at designing a brushless motor controller failed
> spectacularly and the covid parts shortage has also made the central parts
> of that design completely unavailable.  In addition, the bulk price for the
> motor controllers I've been using jumped from $56 per to ~$100 per.
>
> Given that, I thought it might be time to get back to the drawing board.
> However, I am not an expert at this sort of thing, so I thought it might be
> good to post what I am thinking and see if I am completely off the
> reservation.
>
> I'm currently using off-brand VESC motor controllers (schematic for normal
> ones here:
> https://vesc-project.com/sites/default/files/Benjamin%20Posts/VESC_6.pdf).
> They are great but do way more than I need.  They can handle sensored and
> sensorless motors and be reconfigured with MANY different options using a
> desktop application.  I don't need to make something that is easy to make
> work for lots of different motors and I don't need to support sensorless
> operation.  I just need to make something that works for my motors.
>
> The approach that the VESC takes is a central microcontroller which talks
> with a (not currently available) DRV8301 chip.  This chip in turn senses
> voltage/current across each motor coil and drives 6 N-channel mosfets to
> control the motor (3 high side, 3 low side).  It does FOC control, which I
> believe is state of the art in terms of smooth motor control. It also
> integrates the 3 halls sensors that sensored motors have if they are
> available.
>
> I'm having trouble finding any of these 6 mosfet motor controller
> optimized gate drivers, so I am thinking that I will just get some high
> side/low side mosfet drivers (like maybe these:
> https://www.mouser.com/ProductDetail/STMicroelectronics/SRK2000A?qs=WHlX%252B%252B9%2FRwCG%2FkukabfLqA%3D%3D)
> and some nice mosfets.  Particularly without dedicated chips being
> available, I'm not going to try to do current or voltage sensing.  I am
> thinking that I would just PWM the 3 half bridges and try to do sinusoidal
> motor control using a STM32 microcontroller to drive it and the hall
> sensors in the motors to estimate position relative to the coils.
>
> If I may ask, does this sound reasonable or am I totally off base?
>
> Thanks,
> Charlie
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-- 
--------------------------------------------------------------
Carl J. Nobile (Software Engineer/API Design)
carl.nobile at gmail.com
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