CNC servo motor sizing - Page 1
Forum section: electronics / general

author: xzswq21
author_rank: Frequent Contributor
timestamp: October 26, 2021, 07:24:10 pm
content: HelloI want to buy a F1210 milling machine from WABECO.https://www.wabeco-remscheid.de/cnc%20milling%20machine%20cc-f1210%20basic%20-1889.htmlthe specification of the original stepper motor is as following:NEMA 34Bipolar current: 6 ABipolar holding torque: 3 N.mRotor inertia: 1450 kg.m2.10e-7Theoretical acceleration: 20600 rad/sec2Ball screw pitch is 5mmStepper angle is 1.8 Degreetravel speed X-axis and Y-axis: 30 - 600 mm/mintravel speed Z-axis: 30 - 400 mm/minBut I want to use ClearPath SDSK servo motors:https://teknic.com/products/clearpath-brushless-dc-servo-motors/all-clearpath-models/which one is suitable for the Machine according to the above specification?Thanks

author: Juha
author_rank: Contributor
timestamp: October 26, 2021, 08:03:03 pm
content: Typically you would size your motor based on mechanics. So based on the load and the speed/acceleration you want you select a motor that can achieve it. Then you would also try to match inertia etc.Assuming the mfgt has chosen the stepper motor based on actual calculations (I doubt) then if example speed doesnt matter just pick something with the same torque.

author: Teknic_Servo
author_rank: Newbie
timestamp: October 28, 2021, 02:40:54 pm
content: Hi xzswq21,I'm an applications engineer with Teknic.It looks like another forum member has already touched on this point but, in general, there are two ways to properly size a servo motor:1. Size the motor based off of an existing motor/motor specifications (such as matching the motor based on its torque and speed output) 2. Doing an in-depth machine analysis where you would calculate moving masses and motion requirements to then come up with inertia, torque, and speed numbers.In either case, please feel free to reach out to us directly for support. You can give us a call at 585-784-7454 or send in a contact request here:https://www.teknic.com/contact/Best regards,Mark D. - Teknic Servo Systems Engineer

author: xzswq21
author_rank: Frequent Contributor
timestamp: October 28, 2021, 05:53:32 pm
content: Can I connect Three or four SDSK-3421S motors at the output of Teknik PowerHub?Do you have any details about the PowerHub? How much power can the PowerHub deliver to the outputs?https://teknic.com/POWER4-HUB/

author: thm_w
author_rank: Super Contributor
timestamp: October 28, 2021, 10:01:35 pm
content: Quote from: xzswq21 on October 28, 2021, 05:53:32 pmIts right in the datasheet:https://www.teknic.com/files/downloads/Clearpath-SC%20User%20Manual.pdfQuoteI have some older Teknic stuff and its great.

author: xzswq21
author_rank: Frequent Contributor
timestamp: October 30, 2021, 06:17:36 pm
content: which motor is better for the WABECO F1210 with ballscrew? SDSK-3421S or SDSK-3411S?Teknik IPC-5 power supply with cooling fan is only 500W, so how the power supply can deliver the below power to three/four motors?Continuous power at 48V:Continuous power at 75V:

author: jmelson
author_rank: Super Contributor
timestamp: October 31, 2021, 08:28:12 pm
content: Holding torque of steppers is an illusion. So above very slow speed, they will not provide the same as holding torque. Servo motors can provide the rated torque at any speed. Also, servos can provide, typically, 4X rated stall torque for short intervals such as one second to deal with accleration. So, a servo with about 1/2 to 1/4 the continuous torque rating can typically outperform a stepper with that holding torque rating.BUT, these Teknik "servos" are just closed-loop steppers, so they don't provide that advantage. This can be clearly seen in your graphs, where the torque falls off linearly with speed. The torque at 500 RPM is half of the zero-speed torque. That is pretty awful. The problem with steppers is they have too many poles, requiring the winding current to be reversed too fast. Thus, the inductance limits the rate at which current can be developed in the windings. A typical stepper has 50 poles, A typical brushless servo has 4 or 8 poles. So, making some assumptions, the torque could be maintained to about 12 times higher speed.Jon

author: xzswq21
author_rank: Frequent Contributor
timestamp: October 31, 2021, 08:46:14 pm
content: Quote from: jmelson on October 31, 2021, 08:28:12 pmStepper Motor vs. ClearPath Servo Motor Demonstration Video:The price of SDSK-3421S is $328 and the price of SDSK-3421S is $349according to the F1210 milling machine, which servo motor in this world do you recommend me?All Clearpath servo motors:https://teknic.com/products/clearpath-brushless-dc-servo-motors/all-clearpath-models/

author: xzswq21
author_rank: Frequent Contributor
timestamp: October 31, 2021, 08:59:02 pm
content: One of Teknik application engineer told this:Quotefor the Video on Youtube:Quote

author: jmelson
author_rank: Super Contributor
timestamp: November 01, 2021, 02:06:00 am
content: Quote from: xzswq21 on October 31, 2021, 08:46:14 pmThe 3421 motor loses all torque at 1000 RPM. The 3411 has SOME torque out to 1700 RPM. What motor speed do you need to achieve to get reasonable linear speeds on the machine tool? I don't know the the leadscrew pitch or gearing, so I can't compute it for you.But, you would probably want to get at least one meter/minute rapid feed. Assuming direct drive to 5 mm pitch screws, that would take 480 RPM, but maybe you'd want to go 50% faster, so 720 RPM. With either of these motors you'd only get about 200 Oz-In torque, so go for the cheaper one. Clearly, at lower speed the 3421 motor gives more torque, but at higher speed, the 3421 drops BELOW the 3411!So, you need to contemplate the speeds you'd be running at.Jon

author: xzswq21
author_rank: Frequent Contributor
timestamp: November 01, 2021, 06:17:41 am
content: Quote from: jmelson on November 01, 2021, 02:06:00 amI really appreciate youI checked ClearPath SDSK motors again and I found another one SDSK-3421P.The price for SDSK-3421S and SDSK-3421P both is $349 and for SDSK-3411S is $328. I have compared the performances at 75v and 48V as following:What do you think about the SDSK-3421P? Which input voltage do you prefer? 48VDC or 75VDC?Actually spindle speed of the WABECO F1210 is only 100 to 3000, someone told me it's low for a CNC, but Spindle speed of WABECO F1210HS=100 to 7500 but if you want to compare their prices:WABECO F1210HS=WABECO F1210+$2320Actually I should spend $500 for the accessories, $500 for the Dividing head, $1170 for ballscrews, and if I want to buy a coolant unit I should spend another $375!plus I should spend 3x$349 for the clearpath motors+$275 for 75VDC Power supply, $100 for the cables and $377 for the controller board!that's why I can not spend another $2320 for Motor upgrading.there may be a solution,I should remove some accessories and coolant unit andI should buy a cheaper dividing head with 0.04mm accuracy:https://www.wabeco-remscheid.de/teilapparate-und-zubehor/dividing-attachments.htmlI think later I can build a coolant unit.plus if I buy a F1200 instead of a F1210, I can save $200. (Work table of F1200 is 50x18cm and Work table of F1210 is 70x18cm)if I remove the ballscrews I can save another $1170! but how much will be the backlash if I don't use the ballscrews?! the servo motors are closed-loop.if I take such a decision I can buy a F1200HS ISO30 edition.Thanks

author: xzswq21
author_rank: Frequent Contributor
timestamp: November 01, 2021, 07:22:24 am
content: a user in the below link explained some tips and I think it's useful and you see the tips as followinghttps://www.cnczone.com/forums/uncategorised-metalworking-machines/97857-cnc.htmlQuotefrom Wikipedia about the cutting speed:https://en.wikipedia.org/wiki/Speeds_and_feeds

author: Doctorandus_P
author_rank: Super Contributor
timestamp: November 01, 2021, 03:33:06 pm
content: Why do you want to use servo motors instead of stepper motors?You can't mill faster with servo motors, because the milling speed is limited by the mill and your workpiece itself.With servo motors you can have faster rapids, but that is usually only a small part of the total cycle time and it's not important for "hobby use". With a small CNC machine the time you can gain with fast rapids is also quite limited. (Compare this with a big router that has axis of over 2 meters long).Fast rapids also have a disadvantage of being able to crash your machine faster then you can push the emergency stop button.I have a small CNC machine with 112 mm long closed loop Nema23 motors and 1605mm ball spindles, and this can have rapids of over 10m/min, but I've limited it to 4m/min as this is plenty fast for me and it gives me some time to push the emergency stop if needed.Closed loop steppers are a nice upgrade, mostly because they run quieter and the motors run cooler.With "real" BLDC servo's you have the added complexity of mandatory fine tuning of PID loops, while stepper motors "just work" (even the closed loop versions. These do have built-in (and adjustable) PID parameters, but it's not very critical).Also: A servo motor is not much different from a stepper motor. The main differences are that stepper motors have a much higher pole count, and 2 phase stepper motors are more common then 3-phase stepper motors. (A two-pase 200 step/rev. motor has a pole count of 50). and this explains why it has more torque at lower RPM, and more difficulty with higher RPM.

author: xzswq21
author_rank: Frequent Contributor
timestamp: November 01, 2021, 06:17:19 pm
content: Quote from: Doctorandus_P on November 01, 2021, 03:33:06 pmBallscrew pitch is 5mm so the required RPM for 4m/min is (4000m/5mm)/min=800If I want to buy a stepper motor I should buy a Stepper driver too, most of the stepper motors are open loop, DO you know a suitable closed-loop stepper motor with a driver?What do you think about the WABECO F1200HS? spindle speed is 100 to 7500, according to the equations and some parameters I think it's better for surface finishing.

author: Doctorandus_P
author_rank: Super Contributor
timestamp: November 01, 2021, 07:01:07 pm
content: I've bought a few Nema 23 closed loop stepper motor sets (motor + driver + cables) for around EUR 100 each.They also need a power supply to work, and some microcontroller (I used a blue pill with GRBL).I can not tell if a higher RPM is very useful to you.The days of HSS tools have mostly gone by, except for cheap drills.Carbide tools run at much higher RPM and an upgrade to 7500 rpm is probably useful, especially if you plan to run a lot of carbide tools with lower diameter.But if this also results in lower torque at lower rpm, then it becomes a difficult choice.Simplified version is that you need a mechanical gearbox (or (timing) belts) to change between high and low gear. If you only have electornic speed control for the whole range from low rpm to high rpm, then you always have (relative) low torque at low rpm and you can't use big face mills as they are intended to be used.On the other hand.If you want high rpm, you can add a 24000rpm spindle later with a bit of tinkering.