The Following User Says Thank You to JAZZCNC For This Useful Post:
They make so much sense, nice vid, it gives you a good idea of what they are capable of
Last edited by george uk; 21-01-2014 at 12:42 AM. Reason: spulling
They are nice but the price+customs+PSU= the price of a good second hand servo. And they are steppers with their good and bad. I was in doubt for 2 weeks and at the end i bought AC servo motors +drives. Which i suppose for the same money will bring the machine to another level.
What i mean is though they seem nice, it seems better to me to go with normal steppers or go to servos.
If these drives/motors are sized correctly for the machine then they match servos for accurecy and absolutley blow them away for ease of use. No messing around with scopes and PID settings etc, just plug-in setup a few simple parameters and forget.
Servo's are great but they can also be a complete night mare and for DIY machine they can be more trouble than there worth with very little gain worth the trouble or cost.!!
21-01-2014 #6If these drives/motors are sized correctly for the machine then they match servos for accurecy and absolutley blow them away for ease of use.
Twinning an X, Accurate Z position over large time running jobs, 4th and 5th Axis positional holding. any CNCing that your likley to loose steps.
Bear in mind that to make a stepper motor system closed loop, above a certain speed you don't need the encoder as the driver can monitor the motor back-emf and accurately infer the rotor position from that. For this reason, if you were to take the stepper motor from this driver and connect it to a driver which uses field oriented control (vector control), (e.g. 2M880N) the performance should be virtually identical above that speed. You can only gain anything below this speed, since whether the position is inferred from an encoder, or the back-emf, doesn't change the rest of the algorithm. That's the reason why the stall detect feature, e.g. on the AM882 driver, only works above 300rpm - it can't sense the position below that speed.
There will be slight differences, beyond the scope of this post, however these will be negligible compared to the gain you get from having a much wider selection of motor ratings with standard stepper systems - e.g. you'll notice the difference buying a 3Nm stepper instead of the 2Nm closed loop one as the closed loop one in general can't gain anything like 50% more torque from the motor.
There is potential for a gain in accuracy due to having the '1000 line' encoder on the stepper motor, however I'd argue that there are few DIY CNC systems which would benefit from correcting the position error that occurs when an torque is applied to an open-loop stepper motor, since it is so small compared to other inaccuracies in the system. Similarly, with an encoder the motor rotation can be 'smoother' at low speeds. Unless you're having big problems with resonance, this is unlikely to be an issue if the system is correctly designed.
Fundamentally, the only difference between this closed loop servo system and a standard servo motor is the number of poles and phases. Stepper motors generally have 50 poles and 2-phases, compared to around 2-6 poles and generally 3 phases for servo motors. That implies lower torque ripple, so smoother speed control, however any modern servo drive will use the field oriented control algorithm, which (if the bandwidth is sufficient) largely eliminates the torque ripple.
I certainly wont be buying any closed-loop stepper systems.
Z Axis, for what i want to do, thats more important, some of the jobs we are looking at have run times going over 5 hours plus, ( am doing 2 machines ), so it seems to be a reliable way of making sure any lost steps in Z dont compound themselves, as they would be corrected immediately.
You can only gain anything below this speed, since whether the position is inferred from an encoder, or the back-emf, doesn't change the rest of the algorithm. That's the reason why the stall detect feature, e.g. on the AM882 driver, only works above 300rpm - it can't sense the position below that speed.
What i meant was that closed loop steppers are still steppers, low torque at high revolutions, which in my case meant i should have compromised with the gantry weight on the 2300x1300 machine i started building or buy a really big closed loop steppers, which in price surpassed second hand AC servo system. The other solution was to make all the gantry from aluminum, but as DIYers like me normally don't have access to machine 1 1/2 meters long pieces of aluminum, this would have raised again considerably the price.
I don't know if i am to obtain another level of headache. But maybe its the time to learn. Reading from the manual of the Samsung servos i have bought, the tuning seems quite simple in fact. If i drive them from the motion control in step mode. According to the manual you introduce some simple parameters, home your machine, push the button and the servos start some test moves and adjust to the machine itself. If that works, it certainly is a non brainer. If doesn't work, there is always something new to learn on the way. Plus i can control them in a couple of different ways also from the motion control board if desired so.
In short i prefer to be free with the design of the machine to be able to construct it the way i like, with the budget i like, to be heavy as necessary, and to drive it as its necessary :-) . As a DIYer i wanted a commercial machine for the money of DIY. That meant some second hand components.
Again the Servo can only watch the following error report back to the motion controller and fault if goes past it's parameters. Positional correction is down to the Controller and if like Mach3 it doesn't have the abiilty to close the loop then position is not corrected.
The Closed loop Stepper system has built in controller to do the correction so it doesn't matter if the Controller sending the pulses doesn't close the loop position is still corrected AND just like a TRUE CLOSED LOOP servo system has the abilty to fault if outside set parameters.
Servo's have there place and like in Silyavski case with a very heavy gantry then I agree they are probably better suited.. . . .BUT . . My original case that for general DIY machines having or needing the luxury of CLOSED LOOP capabilty's still applies and they are much easier and cheaper than servo's plus can be just has accurate if correct size for the machine.
Now are they better than standard Stepper system then YES but only because they Close the Loop at the drive and in the case of the smaller 2Nm which use 3 phase motors with 1.2deg step angle makes for a very smooth running motor. They are no more powerful, faster or anything else and if you don't want the Luxury of Closed loop then with Very good drives then agree they are an expensive Luxury that standard steppers can match other than closing the loop and correcting positional loss.
For DIY slaved axis Stepper systems then IMO they are the DOGs Danglies offering the best all round solution with Minimal hassle of setup and high reliabilty against racking or positional loss.!!. . . . It just comes with a price tag.!!
Would I use them.? . . . . Yes but only on high end machine with Slaved Axis.!
Last edited by JAZZCNC; 21-01-2014 at 10:19 PM.
By Matt81 in forum Motor Drivers & ControllersReplies: 5Last Post: 19-06-2014, 08:08 AM
By JAZZCNC in forum Stepper & Servo MotorsReplies: 10Last Post: 13-10-2012, 04:39 PM
By Leadshine-Erci in forum Stepper & Servo MotorsReplies: 0Last Post: 25-05-2012, 07:11 AM
By funkmonkey in forum Stepper & Servo MotorsReplies: 24Last Post: 18-07-2009, 08:56 PM
By bobin in forum Machine DiscussionReplies: 7Last Post: 20-05-2009, 02:56 PM