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  • Conversion to Stepper Motor...

    Hi, I have an existing electric motor I would like to replace with a more controllable stepper motor & encoder. Specifications of the current motor are 550w 220v 40a. It has a 15mm output shaft driving a 23mm toothed belt.

    Can you advise which stepper motors would be suitable to swap in? Or alternately provide some assistance or advice on where i can find some info that will help me find a stepper motor that will work in this application?


  • #2
    550W sounds like a lot for a stepper. you might be better off with a servo. However, more important than nominal power, is the speed and torque that you actually need. Without knowing the speed and torque range that will be needed it is probably pretty much impossible to recommend a specific stepper. If you say what kind of motor is currently being used e.g. DC, universal, induction etc. and the motor speed one might be able to make an educated guess at the torque, but just knowing "550W" is not enough to specify a stepper, I might feel reasonably confident that say, a 750W Servo could work, but, before spending about $1500 I'd really want more information.

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    • #3
      Thanks for the extra guidance Tinker. The machine in question does not have much documentation. If it helps, the machine is a basic (very basic, very Chinese) VFFS. The motor I want to replace connects through a 90' gearbox to drive a single vertical shaft, which in operates a couple of cams for the moving parts. In terms of torque required, I don't believe it would be too much (it is only really working against some average size springs), but I don't know how to measure or calculate the torque being used to drive it now.

      The other information I have been able to gather in addition to the above is the model no. - YL8024, the speed - 1400RPM and it is referred to in some diagrams as a 'frequency motor'. My searching for datasheets for that model number find details for a 750w motor, so I don't believe the info would be relevant (but I know very little, which is why i',m here)...

      I don't know if that extra speed/RPM info makes things any easier?

      KR
      Andrew

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      • #4
        220v 40a is not 550w. Is 9kw. Some of the motor data is wrong.. my guess the current draw.
        the stepper is used for slow motion, where the motor can still provide the torque, while the incremental motion offers control.
        how slow is slow? Steppers donít offer any speed rating.

        if speed is not an issue and you want to control the motion from plc, then stepper could be a cost-effective option, granted the torque is achievable.
        if the motion needs to be done fully automated, with plc only to start the motion, then servo is the way. More expensive than stepper.

        programming is simpler with servo.

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        • #5
          I know a bit about VFFS machines and that sounds like a main motor for the machine. I doubt you will find a stepper that will suit your needs for this. The speed required will just be a bit more than a stepper motor can do and still supply a good amount of torque. 550w sounds a bit low for a main motor (usually closer to 750w-1kw), but 40a sounds way too much for such a machine.

          I have used some big steppers to give lots of torque (while still rated for high speed), but usually the speed needs to stay under 1000pm. 1400rpm is usually too far past the torque dropoff to be usable on a stepper. I would really have to suggest a 750w servo motor instead. It has the required RPM and a bit more, and maintains the torque you will need out to 2k rpms.

          I do know of two motors that would *maybe* fit your needs, but they are around $1900 each, and thats just motor cost. At that point servo is already cheaper and better.
          Last edited by MikeN; 01-29-2019, 12:26 PM.

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          • #6
            A bit of a correction required. Removed the motor and got a proper look at the manufacturers plate - it is 4.0A, not 40A as originally mentioned.

            With the motor out of the machine I could turn it by hand very easily, so the torque required is not that much...

            Matching the speed/RPM is not an issue. The aim is to actually reduce the speed and get more control over each cycle/revolution (and even some control of timing during the cycle) - hence the stepper solution.

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            • #7
              Originally posted by C-Monsta View Post
              A bit of a correction required. Removed the motor and got a proper look at the manufacturers plate - it is 4.0A, not 40A as originally mentioned.

              With the motor out of the machine I could turn it by hand very easily, so the torque required is not that much...

              Matching the speed/RPM is not an issue. The aim is to actually reduce the speed and get more control over each cycle/revolution (and even some control of timing during the cycle) - hence the stepper solution.
              Even still, no automation direct stepper has the speed and torque you would need unless you plan to run your machine at a maximum speed that is 1/3 what you have right now. And that's still a maybe on if it will work, as the largest stepper motor AD sells has significantly less power than what your current motor is rated at.
              A servo will do everything a stepper can and more, and gives you both a much higher speed range, smoother running, less noise, and more torque. 750w would be what you want.

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              • #8
                " The aim is to actually reduce the speed and get more control over each cycle/revolution (and even some control of timing during the cycle)"
                For speed control I'd think a three phase induction motor with a VFD would be one of the better options as far as cost/performance ratio, (one might also consider a brushed DC more and speed control though I personally prefer VFDs as I've seen a surprising number of SCR DC drives fail). Now operating open loop neither option will give good position, but you say "some control of timing" which doesn't sound too critical to me, with either an encoder or suitably positioned limit switches/sensors and dynamic braking one can achieve some fairly decent positioning.

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