- 0:35 "...flip the switch and see who finishes first..." - both kind of motor steps 1 (probably 1.8 degree) when gets a pulse. Who finishes first ? That one who gets the more pulse per second. Thats a control parameter and depends on you, it has nothing to do with the motors. The servo goes faster becose you controlled so, and you wanted so. But If you want that, the regular stepper goes faster, it depends on you how do you control them. - 0:45 "85% greater torque allows to finish it faster...." - You donno the difference between speed (revolution/second) and torque. Torque has nothing to do with speed, as I said before the speed was higher because you controlled so. Both motor moves the same weight on a similar car, if we put the fragment of second long acceleration phase aside, both motor gives about the same torque in the above example, because their load is about the same. If we compare the torque/revolution curves of these motors, then a stepper goes a slightly lower indeed, but those differences are little, and significant only at higher revolutions 1000 rev/min and higher up to 3000. Most of regular steppers can't even rotate a 3000rev/min, they are designed to low speed. At low speed (like the above test) the torque is about the same, and because the servo was set to 85% higher speed, most probably the regular stepper could give more torque in such a comparison. Could. But in the above test they had the same load they gave the same torque, as I said before. PCB you donno the basics of physics and you teach people. Hmmm. - 2:00 "more repeatable positioning and more accurate performance" - of coures you don't get more accurate positioning at all, you don't understand it PCB. If overloaded, both motor couse fatal a problem on a CNC machine, a spoiled workpiece. The regular stepper stalls (stops and humming only) when overloaded, the servo motor doesn't stall but slips . The real difference is the error signal ! At a servo you'll know about the problem at a regular stepper you will not know (your controll computer I mean) if a failure happened. You stage things up and you say silly false things to sell a servo motor. Of course the servo is better anyway, but it should be, you pay 2 times more for it.
telelaci2 - Thank you your comment! You are correct if we compare two of the same 1.8 degree stepper motors with identical amplifiers and controllers you would see the same functionality and identical speed torque relations. You are also correct in the observation that the controller is the primary difference between the two options. PBC is in no way claiming that one standalone motor is superior to the other. With the StepServo option you move away from just using the amplifier as a means of control giving the Stepper motor with integrated control a mind of its own. A mind which you can use to set electronic gearing adjusting the steps per revolution, acceleration, and deceleration values via programming using proprietary software. In the most general terms, for DC motors voltage is equivalent to maximum speeds and more current would improve the maximum torque. The improved integrated control allows you to manipulate and tune these maximum values but again these would be limited by the power supply you have available. In the case of the motor “stall/failure” the StepServo also comes with a series of outputs and fault parameters that can alert you to the failure/misstep and not just tear through the workpiece in question. You seem well versed in AC/DC motor applications particularly servos and the benefit they bring at high speeds, in certain applications customers are looking for servo level precision but need higher torques that a stepper motor can provide. What we hope to give the customer is a single package that brings with it all of the added benefits of having closed loop feedback and a more technologically advanced control. Have you taken a look at price comparisons of a Servo motor and an equivalently sized StepServo? Another thing to look at would be the cost of purchasing an encoder, controller, and the cost in labor/logistics to assemble this sort of system. Apologies in advance if any of the terminology didn’t quite fit what we were demonstrating. I hope this clears up any misunderstanding and we are happy to answer any other questions or concerns you might have. Aleks Kecojević - Application Engineer - Aleks.Kecojevic@pbclinear.com
The traditional stepper motor used is a closed loop (not open as shown in the video) stepper motor with built in encoder and driver. This is quite an improvement from the real traditional open motor with separate driver without encoder. The price difference for that improvement is little compared to upgrading to servo motor.
PCB Linear, thanks for the video. I'm absolutely no stepper/servo expert, I just work with them regularly and there are a few points, I noticed didn't seem to reflect with my experiences: - You can use encoders on steppers too, also making it closed loop. It's not unique to servo's. I have done this in several projects, although in my experience, I agree closed loop systems seem to be easier with servo's. (Especially when you start fine-tuning) (btw, I've also done this with 3 phase asynchronous motors and frequency controllers, which was not ideal but worked sufficiently stable for that specific application) - The position of the box with the controller electronics, that depends on what you buy. I always keep the controllers away from the motor, which is much easier to diagnose and replace, if problems occur. Example: in CNC machines, there is too much cooling flying around, so controllers in the control cabinet, motors in the machine. (but that's just my opinion and experience. I also saw 3 phase motors with frequency controllers built on the motor.) - Servo's are not necessarily higher torque or more accurate. It also depends on the motor/gearbox combo and the way it is controlled. I've managed to get a precision with steppers of 20µm (closed loop) and quite some heavy loads, but it was veeeeeeeryyyyy sloooooow and yet, relatively low cost. Servo's would probably have been the better choice here, but were quite a bit more expensive in that particular application.
can you help me a little bit? I am not able to understand the difference between a step servo and servo motor...(main doubt) also, are servo motors are just dc motors with encoders fit in it?
In this situation, closed-loop probably means current is set by a control loop. Adding an encoder lets one measure error, but implementing the control loop will require a bit more work, and provides on-demand torque demonstrated.
When the driver is on the motor it will get hotter, not cooler! it is bad for the driver, and if one fails so is the other and you have to replace both. I don't think it is such a great setup. And the servo motor is so cheap today I don't see any reason to use the stepper any longer...
That depends a lot, but it tends to be true. On a closed loop system, you do not need to keep a large current to hold the position, so you don't heat up the stepper nearly as much as with an open loop one, where you just simply require a larger hold current just in case, to have enough torque for the worst case scenario. Actually on an closed loop one you can downright turn off the stepper if you are on a full step position, and only apply current to get back to the position if it ever needs. The steppers also heat up a lot less when moving than when holding at the same current, since all that current is producing no power on the axis when in hold. Even the running current can actually be scaled up on-the-fly, since you just need to increase it until it hits the position required at the time required, you don't need to run them continuously at full blast. This is even true for low cost closed-loop steppers like those for 3D printers/CNCs found on Aliexpress. I have a pair of Bigtreetech S42Bs on my machine and the steppers run very cold all the time, running or stopped, and so does the driver (because of the aforementioned reasons).
