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  1. #21
    Chaz's Avatar
    Lives in Ickenham, West London, United Kingdom. Last Activity: 2 Weeks Ago Has been a member for 9-10 years. Has a total post count of 1,600. Received thanks 110 times, giving thanks to others 69 times.
    My Triac uses 400W Kinco servos and works well.

  2. #22
    were not talking about money here were talking about a good setup and a good setup doesn't come cheap.

    anything is cheaper than buying datron or haas machine.

  3. #23
    Quote Originally Posted by Skiprat View Post
    I bought a full set up of hybrid closed loop stepper motors and associated drivers etc (Purelogic and leadshine) from Zappautomation a few years back and have had nothing but praise for the setup and zappautomation.
    Closed loop does exactly what i wanted and i think i oversized the hybrid steppers but at least i can sit on the machine and take a ride...obviously only done under the influence of alcohol ..

    Tommy
    I'm also running closed loop leadshine steppers and drivers, very happy with them.
    Last edited by Zeeflyboy; 26-03-2017 at 10:11 PM.

  4. #24

  5. #25
    Yes, looks to be the same as what I'm using.

    They are nice, work great for me... but then I've never used servos so can't comment on that front. Even if you just view them as normal steppers they are a good (if not the cheapest) option in my opinion, they are quite literally plug and play with no tuning required at all and are very quiet, smooth at all speeds, stay very cool in operation and have the must-have features such as stall detection and error signal.

    It was quite fun playing around with the closed loop system before installing them. You can fit a coupling to the shaft and then try to prevent it from rotating as an experiment. Long before it will throw a fault and disable the drive, you can see a sort of rubber band effect.... where a normal stepper would have thrown steps, these keep trying to fight you and then just ping back into place once you release them.

    In theory the closed loop stuff also has better torque curves, acceleration and speed due to the controller having a better idea of what position the motor is actually in, along with higher efficiency and lower noise.

    Edit:

    Quite an interesting read on closed vs open loop steppers where they've actually done some lab testing http://www.motioncontroltips.com/tor...epper-systems/
    Last edited by Zeeflyboy; 26-03-2017 at 10:45 PM.

  6. #26
    Servos i like just for the pure pleasure of watching them move fast and silently. I could stand an hour watching my machine doing ultra fast high speed machining just cutting the air... Its just pure joy watching 200kg gantry accelerate, in fact its quite unsettling sometimes and my hair raises when i run a slow program and when program finishes and machine go to 0 with astonishing speed. For sure wakes me up.
    project 1 , 2, Dust Shoe ...

  7. #27
    are they actually proper servo's or "Chinese" servos?

    the price is great, cheaper than I was expecting to pay for a new setup and if they work well then excellent

    http://www.ebay.co.uk/itm/CNC-Leadsh...c=1&rmvSB=true

  8. #28
    Quote Originally Posted by andy_con View Post
    are they actually proper servo's or "Chinese" servos?

    the price is great, cheaper than I was expecting to pay for a new setup and if they work well then excellent

    http://www.ebay.co.uk/itm/CNC-Leadsh...c=1&rmvSB=true
    They are 100% steppers not servos. They are however 3 phase steppers rather than 2 phase which is standard hybrid stepper. This means they run little smoother with slightly higher torque. Also take note that larger motor sizes above 3Nm are only 2 phase so offer no advantage over normal stepper.

    Now don't be fooled by Comparison Zeeflyboy posted because IMO it wasn't a fair comparison.? They made no mention of the open loop stepper drive used and given the results which are massively off from my experience between open and closed loop steppers suggests to me they used Old technolgy drives.

    New modern Digital drives like EM/AM from lead shine are world apart from old Analog drives and my experience with using both (I was one the first to test leadshine Closed loop drives) is that other than being little smoother because of motor difference there isn't much between them. In fact the AM/EM can be run with more voltage so can be run faster.

    The Example Zeeflyboy gave of motor playing catch up is great when playing on the bench but in real world means very little because if did fall behind the error will still show in the finished part. The controller knows nothing about the error because the loop is only closed between drive & motor. This means there will be discrepancy and errors between axis has the controller just carrys on pumping out pulses for each axis and doesn't allow for fact one axis falling behind.
    This means there is no difference between Closed or Open loop in real world of cutting provided the open loop is correctly tuned/sized.

    The only difference or advantage of closed loop is that you can set the Max following error allowed in which case it will then fault the drive. This is exactly how servo drive works and why they get the name "Hybrid servo" because they work just like servos do. However they don't have the positional accuracy or linear torque servo's provide.
    People think that because they always return to same place due to encoder positioning this is good. Which it is to some small degree. However it can also mask other issues in the system which show in the work but would normaly be seen due to not coming back to same place.!! . . . Things are not always good as they appear.!

    To me bottom line is if you want high feeds/accelleration/smoothness then you need REAL servos. If you just want accurate machine which is reliable and easy to setup etc then save your money and go with standard stepper system with Digital drives like EM/AM.
    Last edited by JAZZCNC; 27-03-2017 at 08:12 PM.

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  10. #29
    Quote Originally Posted by andy_con View Post
    are they actually proper servo's or "Chinese" servos?

    the price is great, cheaper than I was expecting to pay for a new setup and if they work well then excellent

    http://www.ebay.co.uk/itm/CNC-Leadsh...c=1&rmvSB=true
    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.

    As for being able to use higher voltage, the model he linked to is also rated to 2,000rpm - higher voltage is unlikely to help you get beyond that speed on traditional drives I would say? The closed loop steppers manage to maintain higher torque at high speeds too when compared to open loop which is useful to consider when talking about performance at higher speeds.

    As to the playing catch up - it really depends on what you are making and where the problem occurs. Lets say your g-code has a slight blip and you lead out from a contouring cut into a full depth cut of the surrounding stock (it's happened to me!) - were open loop steppers to lose some steps from that they would then go on to ruin your work piece where the closed loop would have caught back up before it even moved to the next operation... also depending on the work and the point that it happens, a small defect may be acceptable (or may not even show on the final piece if it happened while clearing or doing any work away from a final contour or surface) and the rest of the operation would still be dimensionally correct. Lost steps would go on to offset the entire work from then on and completely ruin the whole piece.

    As I said, if you just view them as normal steppers I think they are a good choice, and arguably one of the better choices if staying with steppers. They aren't really that much more expensive than good digital drives and decent quality stepper motors but do honestly have some advantages too so if the extra expense isn't an issue then I don't see why you shouldn't consider them among your options. Personally I just consider them as a high end stepper system, and they've fulfilled all my expectations so all I can say is I've been very happy with them

    Last edited by Zeeflyboy; 28-03-2017 at 09:51 AM.

  11. #30
    Quote Originally Posted by Zeeflyboy View Post
    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.!!

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