Stepper or Servo Motor for high Torque
Hi, everyone I have a winding machine with nema 34 12nm stepper motor open loop. The machine is used to wind coils with copper wire. I plan to upgrade the motor with stronger one. My working rpm is between 50 and 1000(minimum 600 best 1000) , I need max torque from 50 to 100rpm. In those range im working with thick wire (2mm+diameter), so if i work with thinner wires, I increase the RPM, so the torque I need there is less. (the higher the rpm, the lower the torque i need)
I want to ask which motor of these will have the most torque, I guess the servo motor must be geared 3:1 or more for good torque.
For example stepper motor is rated at 20N.m lets say at 50rpm(it will be lower at higher rpm but in my case is not a problem), On the other hand the servo motor is rated 6nm for every RPM 0-2500. If use belt for Servo motor 4:1 it will have 24N.m for every RPM it works?? So its rpm will be 0-625 24N.m ? That means the servo will have high torque for all speeds but the stepper will have high torque only for low speed.
During my calculation I think the servo motor (4:1 belt) will be stronger than the stepper 24nm>20nm, if i use 5:1 belt it will be even stronger 30Nm for rpm 0-500
In this case the servo motor is better than the stepper and the price is the same (too good to be real?) Or just the stepper is overpriced?
The price of the both motor is the same.
I cant use other type of motors because my software works with steppers or servos,
Or You Can recommend me good motor for my aplication up to 500-600 Euros, The 2 motors are just for example
https://www.aliexpress.com/item/1005...d=U6fau0jzBoZu
https://www.aliexpress.com/item/1005...d=ppDYdR92A10M
What about this motor rated at 3.3NM 6000rpm
https://www.aliexpress.com/item/1005...d=S67rWKRQ4dEy
With Belt 10:1 i will have 33Nm for rpm 0-600 this is even stronger from other 2 motors and cheaper? Correct me if Im wrong.
Re: Stepper or Servo Motor for high Torque
Hi Vilyoo - You have done the math and seems the servo is the go. The other ting with a servo is that it can be overdriven. This means if there is a an overload the motor will increase its torque output briefly overcoming the overload. A stepper does not overdrive but stalls if overloaded... Peter
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Re: Stepper or Servo Motor for high Torque
Thank you, Peter. I guess i can check motor temperature once in a while. One more question about the software. I use atmega 8. The software is made for stepper motor 1.8 degree. What option do i need to change to use servo? how many degree is the servo?
Re: Stepper or Servo Motor for high Torque
Sorry Vilyoo - haven't used servos before, on the list for next machine as the prices are really good now. They don't have steps but have an encoder. Peter
Re: Stepper or Servo Motor for high Torque
I havent use servos either, So im a bit confused if i buy servo how to make it work with these settings. I see some steppers are 1.2 degree, so if i want to change 1.8 degree to 1.2 degree motor i just change 200 to 300 in this software and it will work. But with AC servo...??? This software counts the number of turns when motor spins, So this settings is important. I dont have any sensor attached to measure the turns, it is software thing...
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Re: Stepper or Servo Motor for high Torque
Hi,
I use AC servos and they are superb. They have a feature called 'Electronic Gearing' which allows you to program them very precisely to exactly what you require, very versatile.
I would reccomend a gearbox rather than a belt. I bought this gearbox a month or so ago off Ebay. Its superb quality, <1 arc min backlash, 6.75:1 reduction and up to10hp input and paid $180USD for it, bargain!
There are many gearboxes of this type, this one I bought just yesterday for another project, not the same low lash admittedly and 20:1 reduction for $89.90USD. The output shaft is 25mm diameter so should be plenty
big enough for a winder that you describe.
https://www.ebay.com/itm/22480529252...6082%7Ciid%3A1
Craig
Re: Stepper or Servo Motor for high Torque
Quote:
Originally Posted by
Vilyoo
I guess the servo motor must be geared 3:1 or more for good torque.
.
A servo motor is typically maxim torque at zero RPM with a fairly flat curve and starts dropping slightly when max rpm is reached.
One of the motors is 1.25 HP do you require that much?, if so, if no really high RPM's are required, then gearing offers the ability to use a much smaller motor.
BTW, there are stepper drives that will have a feature of maintaining a decent torque level, that normally drops off as rpm increases, if no steps are taken.
For efficient use when using a servo however, closed loop should be considered.
What software are you using?.
Re: Stepper or Servo Motor for high Torque
Hi,
Quote:
i just change 200 to 300 in this software and it will work. But with AC servo...??? This software counts the number of turns when motor spins, So this settings is important. I dont have any sensor attached to measure the turns, it is software thing...
I use Delta B2 series servos which have a 160,000 count per rev encoder. You could theoretically have one step equal to 1/160,000 of a rev or 8.1 arc seconds!!!
All a little bit ridiculous for your winder but using Electronic Gearing you could make that 331 pulse per rev, or 521 pulse per rev or whatever other number works with
your chosen software and motion controller, which can of course include the reduction of your gearbox/belt drive. Easy.
Craig
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Re: Stepper or Servo Motor for high Torque
Hi Craig, unfortunately i cannot use gear box because i already made the spindle.
Hi Al_The_Man, the software is DIY i found in a forum, i have the source code so i can edit it. It uses Atmega microcontrollers.
some photos of the spindle and electronics.
Re: Stepper or Servo Motor for high Torque
Hi,
with that arrangement I would use an inline gear box with the pulley on the output shaft.
https://www.ebay.com/itm/25467196994...Bk9SR9DD-oDYYQ
You can select the gear reduction from as little as 5:1 up to 100:1 and it accepts 60mm steppers or servos. Just chose the gear ratio to get your desired torque.
Craig
Re: Stepper or Servo Motor for high Torque
I decided to go with stepper motor. Nema 42 closed loop 20N.m.
The reason is because it has better holding torque and easy installation.
If gear down the servo motor to increase the torque I will not have high rpm.
Re: Stepper or Servo Motor for high Torque
Hi,
Quote:
If gear down the servo motor to increase the torque I will not have high rpm.
A servo typically is rated to 3000 rpm, even if its reduced by 20:1 that's is still 150rpm. A 42 size stepper is likely to go no faster before stalling.
The most cogent reason for using servos in CNC equipment is speed, steppers stutter and stall at speed where servos just keep going. Whether the expense of a servo is justified
for your machine is questionable, a stepper will probably be OK.
Craig
Re: Stepper or Servo Motor for high Torque
My current motor nema 34 12nm, works up to 900rpm. I can stop it with one finger but at this rpm the wire I wind is 0.1-0.2mm and it works fine.
Will the nema 42 work with 900rpm too?, I cant find rpm chart for it.
I really want to use servo because it will have flat torque curve for all rpm but I'm not sure If it can work with my software
Re: Stepper or Servo Motor for high Torque
Hi,
Quote:
Will the nema 42 work with 900rpm too?, I cant find rpm chart for it.
Probably not. All steppers lose torque the faster they go, that's just plain physics. The determinant of how bad that torque degradation will be is 'winding inductance', the lower the better.
A low inductance 23 size stepper of 450 oz.in holding torque and 1.5mH inductance will have about 40% of its torque remaining at 1000rpm, say 180oz.in.
A medium inductance 23 size stepper of the same 450oz.in but 4mH inductance will have less than 10% of its torque remaining at 1000 rpm, say 45oz.in.
The manufacturers of stepper know that most buyers have no idea what inductance is or how it affects stepper performance at speed. So they make high torque motors but are also high inductance.
I mean you'd buy a 20Nm stepper rather than a 12Nm stepper, the more torque the better right? Well not always, a low inductance stepper of only modest torque will still have more torque at 1000rpm
whereas the high torque, high inductance stepper cant even get to 1000 rpm because it stalls at 500rpm!
This is the advice I offer to newcomers:
For a 23/24 size stepper 1mH-2mH, 1mH preferred and reject anything over 2mH.
For a 34 size stepper 2mH-4mH, 2mH preferred and reject anything over 4mH.
I have not studied the torque speed diagrams for 42 size motors so I cant offer any advice there....but these big motors have truly excellent torque figures but seldom go faster than
500rpm and tend to suffer mid-band resonance. Many people have bought them only to find in practice they don't work like you imagine they would.
The classic technique to overcome the diminishing torque problem is to use the highest possible voltage driver and power supply. Most good stepper drivers are 80VDC capable but if you want to drive a 42 size stepper
then you want more, a lot more, I'd suggest at least 120VDC. It will help get your steppers going at speed with at least some usable torque.
If you really want to spin your winder a 900 rpm get yourself a servo....I don't care that they are expensive, I don't care if they need a gear reducer, THEY KICK ARSE!!! and humble any stepper ever made.
Craig
Re: Stepper or Servo Motor for high Torque
Thanks alot for the useful information, I'll be looking for proper servo motor.
I'm thinking for something like 5-6N.m servo 3000rpm with belt 4:1.. so max speed will be 750rpm which is fine for me.
I have some belts htd 5m -20mm width and gear wheel 20t, now I just need 80t wheel but it is 50 Euros.. do you think a 3d printed one will survive :D
Re: Stepper or Servo Motor for high Torque
Hi,
Quote:
now I just need 80t wheel but it is 50 Euros.. do you think a 3d printed one will survive
You are talking about 20Nm output torque and I'm dubious that a printed pulley will stand up to that.
Quote:
I'm thinking for something like 5-6N.m servo 3000rpm
That is quite a large servo. Typically servos of that torque are somewhat less than 3000rpm. This is a 2kW Delta servo, 6.4Nm at 3000:
https://www.fasttobuy.com/delta-2kw-...nc_p33936.html
I use 750W Delta B2 series servos, ie 1 hp or 2.4Nm at 3000rpm (rated) or 5000rpm (max). They pack a punch that would make you think they have a lot more power than the specs suggest,
and cheaper too. Are you sure you need that torque at that speed?
https://www.fasttobuy.com/flange-80m...er_p28084.html
I've bought three of them over the last month, two for my fourth and fifth axis and another for a retro-fit I'm doing.
Craig
Re: Stepper or Servo Motor for high Torque
Quote:
Originally Posted by
Vilyoo
Thanks alot for the useful information, I'll be looking for proper servo motor.
I'm thinking for something like 5-6N.m servo 3000rpm with belt 4:1.. so max speed will be 750rpm which is fine for me.
I have some belts htd 5m -20mm width and gear wheel 20t, now I just need 80t wheel but it is 50 Euros.. do you think a 3d printed one will survive :D
At 24Nm that will be quite the wire winder, of course, that torque will only be constant with closed loop control.
Re: Stepper or Servo Motor for high Torque
Hi,
a wire winder???, i seen winches which have lesser motors, much deeper reduction of course, but 700rpm with 20Nm torque would rip your arm off no trouble.
Craig
Re: Stepper or Servo Motor for high Torque
Well, I only need the maximum torque at low speed 0-50rpm because I wind flat wire 5x5mm. My nema 34 12nm is not strong enough