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Post by Bruce on Jul 1, 2018 14:49:56 GMT
I found this video and thought it was worthy of a posting.
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Post by Derek the Admin on Jul 2, 2018 2:24:28 GMT
Cool video. Thanks for sharing.
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Post by joebob296 on Jul 2, 2018 2:34:40 GMT
Do stepper motors draw only the current they require?
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Post by Bruce on Jul 3, 2018 3:02:32 GMT
The stepper driver has a current limit setting (which is the measured voltage we set to 0.65 on the Carve King) to limit the amount of current going to the motor. Stepper motors operate at or near this max current limit to get the highest torque at zero speed (Holding torque) as well as higher top speeds without burning out the motor. So the current has to be controlled going to the stepper motor. If this current limit setting is set too high you could burn out the stepper motor.
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Post by joebob296 on Jul 3, 2018 5:11:34 GMT
The stepper driver has a current limit setting (which is the measured voltage we set to 0.65 on the Carve King) to limit the amount of current going to the motor. Stepper motors operate at or near this max current limit to get the highest torque at zero speed (Holding torque) as well as higher top speeds without burning out the motor. So the current has to be controlled going to the stepper motor. If this current limit setting is set too high you could burn out the stepper motor. Makes sense. So lets say your just jogging the machine in the x direction under no load, then you run a program to cut some Aluminum in the X direction. Does the motor draw the same current? Or does the driver just set the max; meaning if less is required to move they draw less, but if needed they can draw up to the max limit set by the driver.
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Post by Bruce on Jul 3, 2018 17:31:50 GMT
Stepper motors are different than regular AC or DC motors where current draw is related to the amount of load applied to the motor. Stepper motors are used for positioning and when they get to that position we want it to stay there. As such, the motor load does not have the same effect on a stepper motor. Basically the stepper motor is peddle to the metal all the time as for as current draw is concerned. That's why they get so hot just sitting still. Maximum holding torque at zero RPM = Maximum motor current whether there is load applied to the motor or not.
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Post by Mototech on Jul 3, 2018 20:29:19 GMT
Glad you posted, I never knew how they work and find it really cool. Now I wanna machine my own😁
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Post by Derek the Admin on Jul 3, 2018 22:42:41 GMT
I agree with berogers.
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Post by ricko on Jul 4, 2018 14:24:07 GMT
Thanks, very helpfull, Derek what is the smallest step size in mm for the Power Route.
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Post by Derek the Admin on Jul 5, 2018 1:49:45 GMT
0.01mm is the step resolution on the Power Route.
It’s possible to set lower, but there is some trade off associated with it.
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Post by ricko on Jul 5, 2018 14:40:53 GMT
WOW 10 microns is incredible.
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Post by Bruce on Jul 5, 2018 21:09:36 GMT
That's good to know. So in software like Fusion 360 it doesn't help to set the resolution any higher than 0.01mm ?
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Post by Derek the Admin on Jul 6, 2018 1:16:36 GMT
Not really. That is such a small size that very very few parts actually need that accuracy anyway. 0.01mm is just under 0.0004”. Plus, I’ve seen it achieved before with our machines but I’d not expect them to consistently achieve that.
Also, for anyone curious: The Carve King actually has 0.005mm resolution, though the Power Route is definitely more accurate. These resolutions are a combination of the drive line characteristics and choice of microstep settings, for what it’s worth. The Power Route could have microstepped resolution down to about 0.0015mm on X and Y and even smaller on Z, but the controller wouldn’t keep up with the rapids as they are currently set at that microstep.
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Post by joebob296 on Jul 6, 2018 1:30:24 GMT
What allows the stepper drivers to maintain the current that they do without burning up? Isn't it still just a winding? I burned up quite a few "normal" AC/DC motors by stalling them out; why don't stepper motors do this?
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Post by Derek the Admin on Jul 7, 2018 13:57:22 GMT
"Normal" motors tend to consume more current when they stall. Stepper motors are on the other hand consuming a more constant current no matter the condition.
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