BLDC open-source drive.

Mickster

According to a Google search of the forum, this apparently hasn't been mentioned before.

https://odriverobotics.com

Has step/dir command inputs for those who want to upgrade from steppers to fully closed-loop servo. I'll be using the PWM/dir.

Can handle 48v @100A.

They also use capacitive quadrature encoders from:

https://www.cui.com

This encoder technology is new to me...low cost as well.

This CUI outfit has other cool products that I will definitely be ordering.

The_Master

GOOD FIND!

But I see a problem with shaft rotation resolution. (these motors are six pole?) Which is not an issue only if you are using a gear train. In which case you wouldn't need that kind of power in the first place.

But in certain cases where you need speed and not high resolution, the low inertia is awesome

But I think it's an absolute joke that $5K (or whatver) CNC machine uses stepper motors. For the love of dog my $29 inkjt printer has servo control in it

Mickster

The resolution of a closed-loop position controlled servo motor is limited only by the feedback device. Here they provide a 8192 cpr (counts per revolution) encoder (2048 line x 4). CUI also offer a 4096 line device which will provide 16384 quadrature counts per revolution (0.022 deg shaft angle).

Apart from a spindle drive, I can't think of an application that needs 7200 RPM so I would use some form of reducer anyway.

My forte is dual-loop feedback where I have transducers mounted to both the motor and the load.

Yeah I have no interest in open-loop steppers...how can it be "controlled" when there is no feedback? Imagine trying to control temperature without feedback, for example.

evanh

Master,
As you may have worked out already, these type drive/motor configs don't actually become a stepper. They just emulate one, if wanted. The encoder feedback provides the step resolution, or, if it uses resolver feedback instead then you get to choose the resolution in software.

The_Master

If you go to the website it shows a 10K RPM motor directly coupled to the encoder

Mickster writes:

Mickster wrote: »

CUI also offer a 4096 line device which will provide 16384 quadrature counts per revolution (0.022 deg shaft angle).

Not much usefullness to .022 deg resolution if A/C motor and controller only have 90 deg resolution. These are evidentally R/C airplane motors.

So for any usefullness it will have to be used with a gearbox. In which case they better mount a propeller too, because itll overheat.

evanh

Master,
Those drives are much more sophisticated than that. EDIT: With encoder there is also another feedback called hall-sensors, these combined with modulation allows the drive to proportionally control torque at any angle. With the resolver version there is only the one feedback transducer.

evanh

In a low-precision situation where it's okay to just pickup motion at any point, an electric car for example, the drive can feel for it's poling and rely on monitoring current draw to sort of lock into the brushless permanent magnet motor rotation. In this case, the drive could get away with emulating positional feedback and not actually have any feedback transducers at all.

I don't know if that is actually what is done in EVs though.

Mickster

The_Master wrote: »

Not much usefullness to .022 deg resolution if A/C motor and controller only have 90 deg resolution. These are evidentally R/C airplane motors.

So for any usefullness it will have to be used with a gearbox. In which case they better mount a propeller too, because itll overheat.

The motor is able to maintain any 0.022deg position and hold it there at full current if there is sufficient external influence.
There is nothing new about this; high-end machine-tools and industrial robots have used this technology for many decades now.

Mickster

evanh wrote: »

Master,
As you may have worked out already, these type drive/motor configs don't actually become a stepper. They just emulate one, if wanted. The encoder feedback provides the step resolution, or, if it uses resolver feedback instead then you get to choose the resolution in software.

Yeah I frequently retrofit my control systems to machines with resolver feedback. Fortunately, the motor's drive provides an emulated quadrature encoder output with selectable resolution.