Duet Controlled BLDC driven hotend? (THUNDER)
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Hi,
since Duet3 CAN-FD / CAN support is called out on the website, can anyone share more about the Raptor / Thunder extruder? -
@oliof that's the first I have heard of it.
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BLDCs are usually high speed, low torque motors. I don't see a gearbox or encoder in that extruder, so I wonder how they control the amount of filament extruded and how fast it comes out. It looks like they aren't selling or shipping yet.
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@mrehorstdmd I did a bunch of precision position-based BLDC controls firmware work for a previous employer and given enough money, it's completely possible to replace a stepper with a BLDC motor and high-resolution encoder.
Here's a bit of a test video: https://youtu.be/1xbCxUVSNVs
This used a high-power BLDC motor, a high-resolution incremental encoder, a TI "Insta-spin" motor controller and a TI BLDC motor driver, so it was quite pricey.
https://training.ti.com/introduction-instaspin-bldc-motor-control-solution
I'm not sure how these folks are doing it, and if they'll get it working or not, but it's POSSIBLE.
(I should probably mention that in the video, you're seeing a stepper-motor on the left and a BLDC motor/encoder pair on the right. I was using each motor's armature as an inertial load as I tested stepper vs. BLDC, so it looks a bit strange.)
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@mrehorstdmd
with the right magnet/stator-teeth combo a BLDC motor has an inbuild 7:1 gearbox.
They have plenty of torque ( except gimbal BLDC motors you might had in mind?)I'm more concerned about cogging. They'd need a certain winding-scheme and magnet placement to reduce cogging. I discovered this a few years back and propagated it over 'RC-network' and other RC-communities when DIY BLDC motors where common.
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@o_lampe what's cogging?
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@oliof
When you move a motor by hand you feel the rotor switch between certain positions. Same, but not so strong with hybrid steppers we use now.
Some BLDC motors use 'halbach arrays" for magnet orientation to deal with cogging, but there are easier ways as mentioned above.
