Thread: Superior Electric Steppers
Don't be put off buying from china if you can afford to wait. You'll get AM882 cheap enough. I've used lots both EM and AM there's very little between them in performance terms.
Very good advice as usual. Many thanks.
Just to throw something else into the mix... I contacted Fehlmann (the makers of my mill) and asked them what they used on the modern equivalent of my machine. They now use Omron "Smartstep" servo motors (R88M-G40030h) with a nominal torque of 1.3Nm and a momentary torque of 3.6Nm. 2.6A mains (200v ac) powered driver.
I'm wondering again whether those Leadshine 3ph Nema23 2Nm closed loop steppers wouldn't do the job or is the torque characteristic for a servo very much different to a stepper?
The 1.3Nm is continous meaning thats what you'll get at full motor speed probably 3000rpm. The 3.6Nm is Peak torque which the drive/Motor can handle for limited period of seconds which is often enough to handle high enertia or heavy starting loads. Under heavy loads ie: cutting it will handle anywhere between 1.3nm & 3.6nm for limited periods depending on loads.
Throw into the Mix that because Rpm is often much more than required there will ratio applied so torque actually increases.
Stepper rating on the other hand measured at ZERO RPM and starts to drop as the Rpm's increase. Slowly at first up until point of the Speed curve where it starts to drop quickly untill full motors coils reach full saturation and motor stalls. On 34 motor the speed curve will be aprox 900rpm depending on inductance and voltage used. There'll be little to no torque at 1500rpm.
This is why inductance and Voltage is so important to the speed you get from steppers. Also you throw how stepper is wired into the mix and it can change again.?
If wired parallel you'll get torque higher up the rpm range but less lower down for set voltage. If wired series you'll get pretty much the opposite, Higher torque lower down rpm range but motor will reach saturation much sooner for the same voltage so lower RPM.
Most 34 motors are 4 wire series wound motors and to get any decent speed from them requires High Voltage. Often larger Nm 34's are run with mains voltage drives.
Now for mill you won't require high rpm's so series wound is often Ok. Nema 23 motors often come with 8 wires and can be wired series or parallel. But the same applies in that higher voltage is required for same rpm if series wound.
So in nut shell if they Fit 1.3nm Servos then 2Nm Nema 23 Stepper isn't going to cut it really.
Last edited by JAZZCNC; 19-11-2016 at 04:19 PM.
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Very clear reply - thanks.
OK, so just to confuse myself more I've tried to fill out the Excel motor calculator here - http://www.mycncuk.com/threads/1524-...otor-do-I-need
I've attached the calculation with what I think are generous values using the Leadshine 3ph 2Nm motors LS2NmMotorCalcs.xls
This seems to look OK, but have I missed something - are my estimates as to load mass and table speed too low? The 3ph 2Nm Leadshine motors have an encouragingly flat torque curve at less than 360rpm -
If I go for conventional steppers I'll go with the AM822 drivers, but what size motor? The old steppers have a surprisingly small shaft (3/8") so Nema34s with 14mm shaft are a bit of nuisance. I see Nema23 3Nm motors with 10mm shafts - http://r.ebay.com/KuT9Ez - Are these big enough though?
Sorry for all the questions.
Just to give some idea of the sort of machine - here's a (bad) photo:
As you can see, it's a kind of mill-drill. But don't be fooled, this thing is a beast weighing in at about a tonne. The table weighs around 150kg - hence my 100kg load per axis estimate. The motors drive the ball-screws directly.
Last edited by Agathon; 19-11-2016 at 05:36 PM.
My gut instinct for a machine like that with direct drive steppers, would be something in the 4Nm range to give plenty safety margin.
I think personally I'd consider altering things to use a belt drive with some Nema23 steppers, which should give you better performance. With big Nema34 motors, for best performance you've really got to use high voltage drivers, but you're then still limited at torque drops of quite quickly with big steppers.Avoiding the rubbish customer service from AluminiumWarehouse since July '13.
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