I once got the idea I could control a brushless motor by being "clever"
controlling set of drivers. I was mistaken. Without some means of
sensing the behavior of the motor, whether it be back EMF or some other
feedback it's about 99% of hopeless. Which is to say I was too stubborn
to give up and managed to see the motor (from a server disk drive) spin,
but if I squinted at it there was misbehavior. A truly silly waste of time.
-Pete
On 10/5/21 12:45, R Radford via TriEmbed wrote:
Carl, Charles is looking for a brushless controller, not just a DC
motor driver. Brushless motors are closer to a stepper motor than a
regular DC motor, but the 'steps' are controlled by sensing hall
effect sensors to know when to step to keep the motor running smoothly.
They are great as they have less mechanical issues over time (no
brushes to replace) and also produce less electrical noise.
The circuit you show is a nice DC to PWM circuit that is similar to
one I did many years ago, but now most (all?) microprocessors have
built in hardware assist PWM so that part is already handled. The
first time I used a similar circuit was controlling a robot from a 286
PC based robot where I used the parallel port to drive an R2R D/A
circuit comparing against a triangle wave similar to your circuit. It
worked great at the time, but now would not be needed. I still have
that old hardware somewhere - perhaps I should pull it out and upgrade it.
On Tue, Oct 5, 2021 at 12:02 PM Carl Nobile via TriEmbed
<[email protected]> wrote:
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
<[email protected]> 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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