Hybrid steppers or servos?

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04 Sep 2020 16:28 - 04 Sep 2020 17:36 #180703 by RoberCNC
I intend to improve my MILLING machine by changing the steppers it works with now but I don't know if I can go to servos or for now I will have to settle for hybrid closed loop steppers. Here are the restrictions that I must adhere to for the moment to see if you can help me.

1- The frame size must be nema 23.
2- Since I do not want to change the electronics (table 7i76) they must be step and direction.
3-The specifications must be at least equal to the steppers that I have or higher, they are about 23HS9430, holding Torque 2.8Nm and detent Torque 12Nm.
4-Maybe the most important, I am not familiar with servos nothing more than there is AC and DC and little more that I have read in this forum, the rest of parameters I have no idea if the higher the value is better or vice versa as inductance, etc. I don't even know where they can be purchased beyond AliExpress, which offer little information and I can't quite trust it.

I would appreciate all kinds of opinions on the matter as well as any reference where to buy them and especially where I can find out to acquire a little more knowledge.

Thank you.
Last edit: 04 Sep 2020 17:36 by RoberCNC.

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04 Sep 2020 16:56 #180709 by tommylight
The short answer would be : don't !
If everything is working properly, there is little gain and to much trouble, especially adding encoders to the mix of plasma interference, that makes shielding and grounding more challenging.
Another issue with servos is that if a part gets in the way, they will break something trying to keep position, while steppers just stall and you end up with some scrap material.
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04 Sep 2020 17:17 #180715 by RoberCNC
Replied by RoberCNC on topic Hybrid steppers or servos?
And the long answer and considering that it is not a plasma? :P :P :P It is a milling machine, and the reason for changing them is precisely that, I do not trust the loss of steps of the steppers

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04 Sep 2020 17:24 #180717 by Mud
Replied by Mud on topic Hybrid steppers or servos?
My plasma is the first machine I've built with 'hybrid' steppers, but I only went for them because the performance looked good and I was a bit curious. I don't think they'll save you from lost steps in any meaningful way, but will shut off the machine if the error is too high*. The encoders only run on 5V, so long and easily-affected cables I'm afraid!

*in fact, if you don't wire in the alarms you'll have individual drivers go down and a potentially even more dangerous situation...

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04 Sep 2020 18:04 #180723 by RoberCNC
Replied by RoberCNC on topic Hybrid steppers or servos?
I understand, that I had read, that what hybrids do is allow the error to accumulate for a certain time and then they raise the alarm by stopping. So I think the answer would be to go to servos if I want reliability and precision, right?

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04 Sep 2020 18:34 - 04 Sep 2020 18:36 #180728 by Todd Zuercher
I am pretty sure that most hybrid closed loop steppers technically are a form of servo.
And most also use the feed back to control the amount of current applied to the motor. Reducing power when not needed, and increasing it when it must. Allowing for higher torques and speeds than would be possible with the same motor if run as a regular open loop stepper.

PS I've noticed the industry also markets "Hybrid Step Motors" that are just what we would call ordinary modern step motors. They simply use better magnets and designs than the old fashion round step motors. (this name predates the new closed loop steppers)
Last edit: 04 Sep 2020 18:36 by Todd Zuercher.

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04 Sep 2020 19:03 #180732 by RoberCNC
Replied by RoberCNC on topic Hybrid steppers or servos?
It is another of many improvements that I wanted to implement, with a stepper at the end the energy consumption is constant, they get hot, hum and speed comes at the cost of losing torque. As far as I know that does not happen with the servos, with the hybrids if I understand that if they do not move they go into rest and stop consuming, heating up and buzzing about losing torque at a higher speed I'm not sure but I understand that it does, since it doesn't they are no longer steppers.

Where can I look at servos with the features I have mentioned?

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04 Sep 2020 20:05 #180745 by Todd Zuercher
If you are converting a machine that was using steppers to servos. I would recommend the hybrid closed loop steppers because, steppers have a very different speed/torque profile than a servo. Servos tend to need a much higher gear reduction than a comparable stepper. So to get the same performance you will likely need to change your gearing to match (probably something like 3-5x).

Teknic makes a servo product that is intended as stepper replacements (Clearpath-SD), but there are probably other more economic options out there.
www.teknic.com/products/clearpath-brushl...3EAAYASACEgIYB_D_BwE
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04 Sep 2020 20:30 #180748 by tommylight
Sorry i thought it is for a plasma.
For a mill i would go with servos and i would avoid Tecnic (sorry Todd ) as i still remember them selling closed loop stepper motors as servo motors and that was a blatant lie.
Since we are having at it, the naming of "hybrid stepper motors" for closed loop stepper systems is also wrong, as "Hybrid" are the normal stepper motors, Vexta has plenty of info on why and how.
To add to the topic, i would be willing to go with some cheap chinese servo drive/motors just to see how good they are as the price of one such system is very close to a good stepper drive, but beware that most of them do come not tuned at all and setting them up is a pain.
Do take into consideration all of the remarks made by Todd, he has a lot of experience with servo systems and VFD's.
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04 Sep 2020 21:04 #180756 by BeagleBrainz
I just bought a servo driver setup to use as a spindle on my mill. I went directly through DMM, and am really happy with their kit.
Just bear in mind depending on the driver you use there is a lot more in the way of filtering and other gubbons that is recommended before the power gets to the servo drive.

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