Integrated motor and drive

[Old_Phart]

As far as I have been able to find on this forum the integrated motor driver style has only been touched on and never settled.
I'm about to build my first CNC primarily for wood, but I'm sure I will attempt aluminum and probably try steel too. But mostly wood. Its for my retirement hobby.
I'm going to use a CNCRP4848 chassis but I have more time than money so I need to put the electronics together myself.

The mdrive from schnieder seems to be a viable option as in integrates driver and motor in a single package. I would imagine there are other options as well, but does anyone with more experience have an opinion on using this style instead of a gecko 540 solution?
I would be grateful for advise.

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[jfong]

Another one is the Applied Motion STM series of integrated driver/stepper motors. I have a pair that I will be using for a corexy 3d printer. I got them for cheap on eBay $60 for both. They are similar to the Mdrive. They both are very expensive to begin with so not a viable option for many. More for industrial automation. For less than 1/3 the cost, a good stepper motor, external drivers works just as well.

the STM motors are nice though. Anti-resonance, programmable microstep modes. Really fast. Plus a bunch of other features not really needed for a typical cnc.

[Old_Phart]

Yea thats the issue. Do I build this with interesting stuff to entertain myself or with the tried and true. I might have a way to get these pretty cheap, if the cost were identical would these be a no brainer or would there still be concerns about them?

My brief understanding is that because of its "intelligence" a smaller motor will work as well as a larger standard motor/driver pair. And there would be less high freq cables running around the machine with less heating of the motors.

Perhaps none of that is a real concern to a hobbyist, and perhaps using these would not be advisable for a production shop because a production shop has the ability to design the machine for a job. But since I have some electronics background these have really got my interest. But I have zero experience with CNC so If they are truly bad news for a CNC I need to be talked down.

[Jim Dawson]

The Teknic ClearPath SD series might be something to look at. https://www.teknic.com/products/clea...-servo-motors/

[jfong]

The "intelligence" doesn't give you any more torque than what the motor is rated for. If you able to purchase the exact same stepper motor and hook it up to a good driver such as Geckodrives/leadshine, the performance would be very similar.

Steppers motors will run hot either way. There isn't much difference in cabling either since you need to supply power, step, direction signals directly to the motor. The step and direction signals are low voltage and can be susceptible to noise. Good shielded wires are still required.

My opinion is if I had the money to purchase these types of motor/drivers for $400-500 each, I would rather get servo motors instead. In this price range, you are looking at brushless servo motors with integrated drivers such as Teknic Clearpath.

[Old_Phart]

Jim and jfong
Thanks for that - I'll look into those Teknic parts now.

the "intelligence" does flatten the torque curve and reduce current when unneeded. Again, this might just be interesting and not much value to the machine quality. I figure I got 10 years left on the planet, I want to exercise my brain the whole way out

[James Newton]

I don't see any advantage. And I see many problems. Step signals need to be high speed and so the cable with that signal must be short. Motor drive signals are slow and the wires can be longer.

[jfong]

Jim and jfong
Thanks for that - I'll look into those Teknic parts now.

the "intelligence" does flatten the torque curve and reduce current when unneeded. Again, this might just be interesting and not much value to the machine quality. I figure I got 10 years left on the planet, I want to exercise my brain the whole way out

All good modern stepper drivers reduce the current to idle when the motor isn't moving. In some situations you need to turn that off so maximum torque is required when at 0 rpm. I have the idle current turned off on my rotary 4th axis stepper driver.

What does flatten the torque curve is higher motor supply voltage and not necessarily any special "intelligence"

Some of the nicer "intelligent" versions do have encoder feedback. It will know when the motor skips any steps and send out a alarm signal. At that point, might as well get a true brushed/brushless servo system.

[jfong]

I don't see any advantage. And I see many problems. Step signals need to be high speed and so the cable with that signal must be short. Motor drive signals are slow and the wires can be longer.

That is true but these industrial motor/drivers also compatible to differential 24v input signaling. In the case of Applied Motion, they have programmable input signal filters to knock out the spurious short pulses (shorter than the typical 1-3usec step pulse width). Granted most hobby diy builds won't be using 24volt signaling and have to settle with 5v single ended thresholds. Good shielded cabling is required. But ya it can be a problem.

Although I never had a problem with 5volt single ended encoder signals running all the way back to the servo motor driver. That shielded cable is always running in parallel with the noisy motor cables. Pretty much same frequency, if not higher than, than the original step pulse signal.

[Old_Phart]

hmmm food for thought.
step signal freq and motor drive freq should be the same shouldn't they?
i.e. step = increment = current level through each motor winding . So if the controller steps, in the servo system I have one pair of low current wires changing state, whereas in the conventional stepper I would have 2 pair of higher current wires changing state.

random thought. 12,800 steps per rev * 1000 rpm = 12.8 mhz? is that right?

[Motor_Guy]

12,800 steps/rev * 1000 RPM = 213 kHz (you forgot to divide 1000 by 60 to convert into rev/sec) Also I'm not sure about the other motors, but the Teknic ClearPath servos have isolation on their step and direction inputs making them pretty much immune to noise. In fact I think they use their inputs with un-shielded cables as long a 55 ft.

[jfong]

hmmm food for thought.
step signal freq and motor drive freq should be the same shouldn't they?
i.e. step = increment = current level through each motor winding . So if the controller steps, in the servo system I have one pair of low current wires changing state, whereas in the conventional stepper I would have 2 pair of higher current wires changing state.

random thought. 12,800 steps per rev * 1000 rpm = 12.8 mhz? is that right?

Not exactly. The output that drives the motor is current limited chopped PWM signal. It could be anywhere from 15khz to 30khz depending on the drive designer.

The microstepping circuit varies the current to each phase depending on what position in the microstep cycle it is, not the frequency. The technology is pretty hard to explain but if you are really interested, there are technical papers available. These type of motor drives have selectable microstepping, usually between 8 and 256 (or more). I like to use 10 microstep setting. On a typical 200 full step per revolution drive, you will then get 2000 microsteps.

2000microstep X 1000rpm = 2,000,000

Divide by 60 to get step pulse frequency = 33,333 Hz.

[Old_Phart]

Ahh, its the little things I forget
I was thinking that square wave would look pretty rounded at the mhz range over normal cables. Thanks for clearing that up.