Anyone here that have experience with the ClearPath servos or other “low-cost” servo systems?
I am thinking about equipping a cnc router table i am building with servos instead of steppers, the machine does have 800x1000mm work area and the X axis is equipped with dual 25mm ballscrews with 5mm pitch, so the max speed the ballscrews can handle safely is about 2300rpm or about 11,5m/min, i am aiming for 10m/min or 2000rpm as rapid speed for X/Y (~400IPM for you guys that only use “freedom units”)
I have some steppers lying around, 500oz/in long stack Nema 23, but i do not really see that they will be able to perform at high speeds…
It depends on the motors, and to some extent your drives, actually your input voltage - but what that may be is dependent on what your drives can handle.
Steppers are limited in the torque they can deliver at speed by their inductive reluctance. So the critical variables are the motor’s inductance, and the voltage you operate them at. The lower the inductance, and the higher the voltage, the faster you can run your motors, before torque drops off.
With the right motors, and drives you should be able to run about twice as fast as you want to go. Somewhere in the 4,500 RPM range. But in order to manage that you’re going to need just the right motors, and good drives (80+ input voltage) too. Oh, and a power supply that puts out that high voltage.
Your other option is to gear the motors up. Tuning servos is no picnic. At least not for folks that aren’t experienced doing it. There’s really no easy solutions.
It is not only about getting the motor to run at a certain speed, there is also that there is force required to move stuff, and steppers tend to have a very steep dropoff in torque, and high holding torque motors tend to have high inductance and be very weak at higher speeds.
@Erik_Cederberg
have you run those motors? They might do the job. Though the inductance on them is a tad on the high side. They’re like no name imports.
It has a designer price tag attached to it too though. But Vexta motors perform. I got a couple little PK266s and they’re sweet. I need to build like a plotter with them, or something.
I was checking out those Clearpath servos… So they don’t need a separate servo driver which is cool. And I see they have some sort of auto tuning software you can run on them which I guess figures out appropriate accelerations and max speed for your machine?
So can these Clearpath servos just be connected to any sort of controller? Would something like a Smoothie board ( @Arthur_Wolf ) or a Cohesion3d Mini ( @raykholo ) be a good board for controlling Clearpath servos?
If the auto tune software is used is that in place of setting the acceleration and max speed settings in Mach3/4, or somehow used in conjunction with Mach3/4 settings?
Yes, would love to hear more @Anthony_Webb , or anyone else using them. What’s your electronics setup and what controller software are you using and how does that work with the Clearpath auto tune software?
If they can take a step/ dir input we can handle it. That makes the mini a pretty good option for a powerful CNC. Even have these cute little signal breakouts for using external drivers.
I have got 3 of the Clearpath servo’s on my for ever building project. They are great and seem to have very good holding power. The only issue i have had with them is using the TinyG the step / Direction was not a high enough voltage to trigger them reliably. So i have had to build 3v to 12v buffer.
They are incredibly quiet and i dont get the noise on the extrusion’s that using steppers seems to give. I maybe able to do a video of it if you are interested?
@Davey_Rance neo7cnc did a video of his newest machine compared to his big one. I’m pretty sure the new one uses clearpath servos and he shows just how quiet it is.
@Erik_Cederberg i just run both motors on the same step / dir output. That way they both get the same number of steps. And as long as you have them both setup in the config with the same number of steps it seems to work.
@Davey_Rance : it probably comes down to how much flex there is in your axis, but I think for example about what happens if one motor stops because of a following error and the other pushes on with full power I might damage the machine
Yep agreed but that dosnt change if you use clearpath servos vs just 2 steppers. There is an output that could be used to trigger fault code back to your CNC controller.
From the manual about using the HLFB.
High-Level Feedback (HLFB). ClearPath’s HLFB output can be set up
to alert the user or control system to one of several conditions. HLFB can
be configured to:
• Change state if a Shutdown occurs.
• Assert when ClearPath is running at your commanded velocity
or torque.
• Assert at the end of a settled move (based on user-defined
settling requirements).
• Output a PWM signal proportional to motor speed.
So you could wire it up so if a fault occured then the HLFB triggers your controller to stop then you get to correct the fault and re-home / zero both axis’s. Will be a bit of a pain but doable and still an issue you would have with any dual drive system.
I think it is just a feeling that a stepper is on the right step or not, but the servo can have a following error that makes me doubt… the info abotut the HLFB was great tough, thanks @Davey_Rance
But if i calculate, in the extreme a clearpath servo with the alarm set to 0.25 rev following error it could be 0.249 turns of each motor, so 1/2 turn in total, with 5mm pitch screws that makes 2,5mm difference, and that will probably not damage the machine…
