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Author Topic: What motor size and driver should I use  (Read 6445 times)

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Re: What motor size and driver should I use
« Reply #10 on: December 07, 2009, 02:02:59 PM »
I have a big machine with DC Servos, GE, the X ans Y axis are 34 Amps. Cont. and the Z axis is 51 Amps. cont. Do you thing that the Dugong drive will work with this DC ServoMotors??

Offline simpson36

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Re: What motor size and driver should I use
« Reply #11 on: December 07, 2009, 05:47:45 PM »
You did not mention voltage, so assuming you are OK with that spec, then it is down to amps. From all of my research and also proved out in my own testing and experience, I can not reccommend anyone use the 'continuous' rating on a servo motor as the basis for sizing servo drives for a machine tool.

The 'continuous' rating is exactly that; the limit of heat dissipation if the motor is producing full power continuously. Unless you are powering a conveyor belt, fan, agitator, vibrator, or some other industrial machine that is truly continuous, you can pretty much ignore that figure. On a mill or similar machine, 'normal' operation is anything but continuous. Repeated momentary peaks (accell/decell) with plenty of 'rest' (running at feedrate) in between is the norm. My assessment in a nutshell is this: consider only the peak. if you have a 50A peak motor and you run it with  Gecko, then what you end up with is a 20A motor. If you run the same 50A peak motor with a Dugong, then for practical purposes, you have a 35A motor. You will only have a 50A motor if you run it with a 50A drive.  

To answer you question directly, yes a Dugong would 'work' (provided the voltage is within spec), but it would limit the available peak amps to 35 and your motors are thirstier than that. The motors will likely run fine, but you will not get the acceleration they are capable of, so you would need to realistically assess your needs in that regard. There is no rule stating that just because you have motors capable of pulling anchor bolts out of the floor, that you have to use all of that power.  At least one poster here has 38A motors running off 20A Geckos and seems satisfied with the setup. HomeshopCNC was mentioned and they have a scope trace puiblished on their site clearly showing the Gecko shutting down the party at 20A, thereby loosing half of the motors performance. I am not saying this is neccessarly a bad thing, but it is a fact to be aware of and consider in your thinking. The performace at 20A might be fine for some applications. Similarly, 35A performance of the Dugong may be acceptable with your big motors, but you will not get the max out of the motors.

One would imagine the peak on your motors is far above the capabilities of any of the 'entry level' drives (including the Dugong) at this price point. Drives that would get the attention of your big motors would be far more expensive, so you have cost factor to weight. My advice is to be realistic in your expectations. If you make an informed decision to sacrifice some performance to save many hundred of dollars on the drives, and your application will perform acceptably without the max acceleration your motors are capable of, then you will have done a good job of selecting drives, IMO.
« Last Edit: December 07, 2009, 06:07:00 PM by simpson36 »
Re: What motor size and driver should I use
« Reply #12 on: December 07, 2009, 05:50:31 PM »
Thanks for your response. They are 90V DC.
Re: What motor size and driver should I use
« Reply #13 on: December 07, 2009, 06:07:24 PM »
I can sacrifice some performance on that machine, because that is better to a useless machine. Also the specs. from new of that machine are not so great regarding speed, It is a 1980 Brown & Sharpe 1500VC, and here in the manual say it is a 400in/min. rapid positioning speed ( I belived It was half of that ). I also send the information to cncdrive.com  and will reply here the answer.  Thanks,

Offline Hood

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Re: What motor size and driver should I use
« Reply #14 on: December 07, 2009, 06:18:13 PM »
You might want to email these guys and see what their price is like, http://www.semis.hit.bg/servoe_d.html
Dont know what they are like but they have seemingly been in the industrial analogue drives market for a long time so should be decent.