Jim,
Thank you for the definition of servo.
I’m using servo interchangeabley with AC servo, and probably should be more specific.
Duke
Jim,
Thank you for the definition of servo.
I’m using servo interchangeabley with AC servo, and probably should be more specific.
Duke
In normal conversation a closed loop system running any machine tool can be called a servo without regard to the exact motor type. So when we say servo motor, it can include any motor type and still be understood. Just language shorthand, but not entirely descriptive.
It really depends on the machine and machine manufacturer. Also it's about price point, steppers are cheaper. Some smaller mills do come with steppers, my little Emco Concept 55 has steppers, as do the Tormach machines, and the old Bridgeport Boss series came with steppers also. Where my Eagle (BP clone) and Haas have servos, as does my lathe. Most of the higher end and higher performance equipment comes with servos, both routers and mills. More accurate and more power. Steppers loose torque rapidly as the RPM increases and this can cause them to lose steps, where any of the servos, with the exception of closed loop steppers, have a nearly flat torque curve from 0 to their rated RPM. The closed loop steppers are kind of a special case, if they lose steps, the drive will attempt to correct the error. Where a more conventional servo drive will just keep adding more power to the motor until the torque limit is reached. At that point the encoder error will become too great or the internal drive electronics or controller will simply throw an error and shut the system down. Or the tool bit will just break, which is normally the case.
Under most conditions, the properly sized axis drives are operating at a small fraction of their rated torque while cutting on any machine. Where the maximum torque is used is in accelerating and decelerating especially during fast rapid moves. Take my lathe for instance, it uses every bit of the max available torque (29NM) of the servo to rapid the 1500lb+ Z axis carriage at 600 IPM over a 6 inch move. It requires a lot of torque to accelerate that much mass to that speed and get it stopped again in that short of a distance, it's frightening to watch it.
Jim Dawson
Sandy, Oregon, USA
I got pointed towards the wrong info by the looks of it.
Just go with something thereabouts.
Also are you belted or direct fed from it to your axis?
Reason I ask is that your existing ones are 2000rpm yes?.
Well many of the new ones around your range are 3000rpm nominal.
So you could now get a pulley an extra 1/3 bigger than what you have..... which means you could get a servo a little smaller.
Bigger pulley / smaller motor / higher motor rpm - would be like having changed nothing. (need to do the math).
(If it's direct drive then the above doesn't matter).
Another good thing about servo's too though is you don't have to fork out for power supplies. Direct mains fed.
That's a chunk saved right there.
Actually they're not bad at all. If you can read a wiring diagram you can get it quite easily.
I have to admit my servo's manual was a bit vague (my first ever servo unit). But if you look at other servo's schematics as well, there are many similarities between all.
I did ask for help and people on here are very helpful. I more or less had it right anyway from the diagrams. It turned out more a confidence thing.
Bill South, I tried to PM you but your inbasket is full and it won't let me send it.
Dazp
these are belt drive with a 1:1 ratio
I am probably going to try to bore out the pulleys that I have and keep the ratio same.
this machine even though it weighs in at almost 4000lbs, doesn't have a huge work area, so rapids don't need to be very quick or I am going to beat the heck out of some limit switches.
work area is only X-Axis 14", Y-Axis 10", Z-Axis 14"
thank you
Duke
just for the sake of whomever reads this thread later on, as of today 15 Aug 2021
DMM servos
to get 2 1Kw motors and drivers as well as one 1.3kw motor and driver directly from DMM would be $1810 not sure if this includes cables
from CNC4PC the same package with cables is $2181
for same spec motors from Lichuan shipped directly from china ordered on Ebay $1310
if ordered on Aliexpress $1324.44 both of these are from Lichuan factory store.
Thanks
Duke
Why is 2500ppr not suitable? How does it compare to the 16 bit single turn absolute encoder on the DMM?
Where are DMM made, I believe they are sold out of Canada but I assumed like most things they are China sourced as well.
I’m not opposed to spending the money on a better product, I’d really rather be an educated consumer that’s why I’m researching a bit before I buy
Thanks
Duke
Yes the DMM systems are sold out of Canada, and made in China to DMM specs. I suspect the quality might be better on the DMM units as opposed to the lesser cost systems direct from China, but I can't prove that.
But most important is the documentation, warranty, and tech support. You are paying for that, and it is worth every penny if you have a problem. I would only buy servos from DMM Tech, or Automation Direct SureServo2 (Delta) products. Tech support from both of these companies is outstanding.
Jim Dawson
Sandy, Oregon, USA
Every part of the DMM system is designed in Canada as well as prototypes design changes and software, there system is manufactured by Dmm in there own Factory which is in China
With a Encoder count that low you would be better off with a closed loop Stepper system
16Bit is 65,536 PPR this does not compare with 2500PPR the higher the Encoder count the smoother the motor will run and have a faster reaction time which are all things a CNC machine needs
They have a 20Bit and a 32Bit Encoder also the 20Bit= 1,048,576 yes that is 1 million PPR which has been the standard for CNC machines for a few years now
The lowest PPR you can use is 14Bit= 16,384 anything lower you will have the jerk factor with your machine movement
Mactec54
No not by what you posted ( made in China to DMM specs. ) I replied to a post of yours a few years ago about DMM having there own factory in China I guess you forgot
Not a big deal, but there is a difference though of having something manufactured in China, and having your own factory in China
Apple is a good example of this, most Brand name Bearing Manufacturer's are in China the list could fill many pages of brand name manufactures in China that have there own Factories
Mactec54
Mactec, it sounds like your pretty deep into DMM motors and sold on their benefits.
as a home hobby guy, I am still having difficulty with spending over $2000 on 3 motors when I still have to replace the spindle motor as well on this machine.
I had a Nema 34 12nm rated closed loop stepper motor that I popped onto the dm4400m this morning and was able to move the each axis with it well on X and Y I was able to get up to over 1000mm/sec^2 accelleration at 5000mm/min before the closed loop kicked the motor off
the cost of 3 12nm closed loop steppers is under $500 for the Mophorns that I have.
I can spend the $2000 on motors if it will really get that much better performance, but having never used AC servos in the past, I am having some reservations.
I am also probably only going to put a 2-3hp spindle motor on this machine, is having the excellent performance of AC servos going to be wasted with such a low HP spindle?
as it stands, I have 1800 in the base machine, and another 1000 in the spindle cartridge, so another 500 for a spindle motor
if I go with AC servos that would put me up to 5300 into the machine with the closed loop steppers Id be at 3800.
like I said, I am open to doing the AC servos if they would really up the performance, but I am having some reservations.
thanks for the input.
Duke
You use what ever you can afford to spend on your machine and you will be happy with it
I agree you have to look at the machine and see if it is worth spending that much on, you may have already spent too much, what is the condition of the machine the ways the Ballscrews Etc.
I used to use only Yaskawa and there cost is more than that for just ( 1 ) motor and drive plus cables Etc. so can easy spend $3K Plus per axis for the best there is
Mactec54
I just ordered DMM AC servos, going to be less expensive to build it this way from the start, than to go back and rebuild it later.
Late to this party.
Jim sold me on DMM servos for my mill rebuild a few years ago.
I ran into trouble with analog +/- 10V feedback to a galil card on my system. The vendor was GREAT with tech. help. NOT going to get that if you buy from china.
Anyway, just another person saying DMM is a good choice for a refit.