Why not brushless motors in direct drive extruders?

alankilian

Here's a video I made probably 7 years ago where I was building a system using a BLDC motor in "position control" mode.

(It looks funny because I have a BLDC motor connected to a stepper motor as an inertial load, so don't look too closely)

This was probably US$500 worth of hardware and a TON of firmware development for me to get it this far.

I loved the TI InstaSpin product and their Piccolo motor-control CPUs and if you're interested also, I would recommend looking into it. (I haven't looked in about 6 years, so this might not be supported anymore.)

https://www.ti.com/tool/DRV8301-69M-KIT

alankilian

@zapta said in Why not brushless motors in direct drive extruders?:

https://odriverobotics.com/

Oh MAN, those look nice! Thanks for the reference.

zapta

@alankilian said in Why not brushless motors in direct drive extruders?:

https://youtu.be/1xbCxUVSNVs

Youtbue says it's private and can't be viewed.

alankilian

@zapta Thanks.

I "Published" it.

I don't think the company I did it for even exists anymore.

Catalin_RO

@zapta Extruding is all about torque at relative low RPM. This is what I see for those really interesting solutions:

Maximum torque 1.99Nm or 3.86Nm, but that comes with a peak current of no less than 65A!!!
A big note - "*Note that torque and current ratings are with Extremely good forced air cooling"
RPM at no load - 5760RPM or 8640RPM.

The torque I get, at much lower speeds of course, from a rather standard NEMA 23 at 2.4A and no need for extra cooling.

And the pricing... the driver is a merely 179EUR. You get 3 or even 4 decent Leadshine drivers for that amount!

Again, that is exactly what I have stated... it is a solution, bot not for extruding the filament! I would see it more likely for the gantry movement where, in a 3D printer, the required torque is very low but the speed is high. But, still, it might not justify the extra costs...

Catalin_RO

@rjenkinsgb said in Why not brushless motors in direct drive extruders?:

They both use permanent magnet rotors and wound stators.
(Steppers do not have plain iron cores - if you turn one, you can feel the rotor magnet jumping from alignment with one stator pole to the next).

Unless they are variable reluctance ones!

rjenkinsgb

@catalin_ro said in Why not brushless motors in direct drive extruders?:

Unless they are variable reluctance ones!

Yes, but only permanent magnet types are used in such as 3D printers, as far as I'm aware?

zapta

@catalin_ro said in Why not brushless motors in direct drive extruders?:

Extruding is all about torque at relative low RPM

I am not an expert but isn't this what gears do, trading between torque and speed?

zapta

@catalin_ro said in Why not brushless motors in direct drive extruders?:

And the pricing... the driver is a merely 179EUR

This is probably a matter of demand. With sufficient demand, this can be a much lower cost IC. The question is, is it useful for large scale applications?

Catalin_RO

@zapta said in Why not brushless motors in direct drive extruders?:

I am not an expert but isn't this what gears do, trading between torque and speed?

Of course, but those gears and their supporting plates start adding to the weight. And the whole discussion started from the 30g BLDC motor.

Catalin_RO

@zapta said in Why not brushless motors in direct drive extruders?:

This is probably a matter of demand. With sufficient demand, this can be a much lower cost IC. The question is, is it useful for large scale applications?

Demand builds up when there is a real need for such a solution. I see a need for it in completely different applications, but not in a 3D printer, not even in a prosumer one. In a professional one, maybe!

Has anyone complained about the steppers limiting the performance or the quality of the 3D printers on this forum? I have not personally checked, but from already 4 years of browsing I don't recall anything significant. Of course, I'm not discussing about faulty steppers or super cheap steppers assembled in a barn in China (by the pigs grown up for feeding the family over the next year) or poorly chosen (wrong size for the job) ones. There are very good quality steppers at very decent prices, most of them manufactured in China. And they are not even difficult to find.

So with a relatively low demand, combined with the high current involved in those drivers (120A peak current! those transistors are anything but cheap!) I don't see the solution getting significantly cheaper. Overall you must also factor in the high current power supply. 24V at 60A is almost 1.5kW peak power for one of these motors. While the average required power is significantly lower, the PSU should be ready to handle those peak currents. Look at this just for reference - https://www.onlinecomponents.com/en/mean-well-usa/rsp200024-43879729.html.

As for recognized professional solutions, check this servo with integrated driver - https://www.sorotec.de/shop/JMC-Servo-Motor-with-integrated-driver-100-Watt---36-Volt---3000-1-min.html. Significant torque with very high speed as 36V and 6A peak current.

zapta

@catalin_ro, I don't know much about the technical aspects or the market potential, to have an opinion.

BTW, Skyentific on youtube often deal with low speed, high torque motors for his robotic actuators. It's an interesting channel. These are high pole count motor, sometimes with additional gearing.

https://www.youtube.com/results?search_query=Skyentific+actuator

Catalin_RO

@zapta Quite interesting. Those might be suitable for axis 4 and 5 in a prosumer CNC...

zapta

This video has a teardown of such an actuator. Plenty of poles and a planetary gear for torque, and a smart builtin controller.

https://www.youtube.com/watch?v=Mhxz2Bj2RXA&t=615s

It's not light and not cheap but interesting.

rjenkinsgb

@zapta said in Why not brushless motors in direct drive extruders?:

Skyentific on youtube often deal with low speed, high torque motors for his robotic actuators.

Those are clones or descendants of the MIT "Cheetah" robot actuators.

They were originally a modified open-loop motor for a large drone, with a hall position sensor and epicyclic gearbox included, to allow them to function as fully commutated BLDCs.

And, they specifically have the ability to be back-driven to accept the weight and shock loading in a robot limb application to emulate biological muscle & limb elasticity, without a high-ratio gearbox that would be damaged by such loading.

The originals are clearly visible in this clip:
https://www.youtube.com/watch?v=xkfXW6XMXao

James Bruton came up with a lower cost DIY version, using generic drone motors with belt reduction rather than the custom epicyclic gearing:
https://youtu.be/Id11PWxnd4M?list=PLuzW8n0FM__UQutfHUF7jf4jbZwmWM1L6&t=196

Pertti

Thanks for everybody showing interest around this topic. Looks like reducing weight increases costs as usual.

Pertti

Ha-haa, here it is,found in Hollow shaft extruder thread:
https://www.youtube.com/watch?v=f0SuaIMxAs0

o_lampe

@Pertti Now you can enjoy your "told you so..." moment. Only 18 month later
ODrive was a starting point, but simpleFOC took the edge off cost-wise. (and it's open source)
Too bad, there are only a few driverboards available. Most of them are DIY projects, which we have to order from jlcpcb.

Pertti

@o_lampe I like this group because of this habit of sharing and commenting innovations.

CNCModeller

@Pertti @o_lampe I've bought the shields from here in the past and they seem to be good quality. It only takes a couple of weeks to arrive in the UK

SimpleFOC Shield v2.0.4 FOC BLDC servo stepper motor controller brushless motor driver board develop card

https://a.aliexpress.com/_mPDYIZC

Why not brushless motors in direct drive extruders?

Robert J.

Robert J.