The Best Steppers/Servos Setup Thread

[JAZZCNC]

They aren't servos at all, they are closed loop steppers...

Jazz - all very well saying don't be fooled by that link, but I have yet to see any quantitive testing that shows there is no or very little difference between closed loop and open loop steppers... all the comparisons I have seen have shown them to be superior. Have you come across any evidence to support the assertion that there are open loop systems that can get close to the efficiency of a closed loop system? The 3 phase ones also have a higher resolution at 1.2 degrees per step rather than the 1.8 of most 2 phase steppers, which is about a 30% improvement.

Zeeflyboy- The reason you probably haven't seen any evidence in tests is because they are trying to sell or promote Closed loop. Also they are not comparing Apples with Apples in most cases.

Like you rightly point out Closed loop motors are 1.2degree and 3 phase. I'd bet strong wagger they are using 2phase 1.8 degree motors on the Open loop test.
I'd also put another wagger that they are not using Digital drives on the Open loop but old Analog drives.

True test would use Digital drives with 3phase motors (which can be bought.) In this case the only difference is the Encoder and Closed loop side of the DSP which doesn't make any difference to performance of the motor. Closed loop drive is just Digital drive with Closed loop option inside the DSP. This can be proven by turning the closed loop side off which can be done via software in some drives. The performance of the motor doesn't change with it turned off.

Do this then the only difference between Digital drives like leadshine EM/AM and the Closed loop system is the motor which is connected. My argument was never that standard steppers equal 3 phase steppers and I said all along 3ph motors are smoother which is mostly because of the 1.2deg resolution.

Now my comments regards standard 1.8 Degree steppers and Digital drives comes from years of experience building machines which use them. My comments regards Closed loop come from using and testing them on several machines over the last 18mths. I can tell you and everyone else that the difference in performance is minimal, yes slightly smoother but thats about it.
Now where the AM/EM drives do trump the Closed loop is that they have 80Vdc limit not 50Vdc. This translates to more speed and more torque which for router is crucial, not so much for mill.

Your argument regards Catching up is weak at best because simple truth is that if falls behind there will be some error. Chances of this happening only on that one axis while others are not moving and on part of the work piece which is not important have Odd's higher than winning the lottery.
What happens if this happens 10hrs into 12hr job of 3D mould with 3 axis moving together cutting expensive piece of aluminium.?? . . . . What good is Closed loop here if falls behind.?

Also if the Open loop is losing steps then it's in-correctly tuned or pushed too hard. In which case this would happen to closed loop just the same if pushed past it's capabilty's. Only difference is it would or should Fault before stalling. Good Digital drives like EM/AM will however quickly Fault when it see's Stall so again very little difference because both have messed up.!!

Now to the Price argument.! . . . I agree Closed loop are now lot cheaper but still they have way to go. AM882 can be bought for £60-70 3-4nm Motor for £35. The Leadshine Closed loop shown was £179 and is only 2Nm.!! . . . . Nearly £80 difference PER AXIS. for very little gain other than bragging rights.!!