Problem driving Steppers - problem with TB6560?
22 Nov 2012 11:59 #26860
by rifraf650
Problem driving Steppers - problem with TB6560? was created by rifraf650
I'm hoping this is the right place to post this. I'm new to the forum, but have so far benefitted greatly from this site in setting up LinuxCNC.
I've got a Probotix V90 with a driver and steppers from A Quick CNC. The driver is a TB6560 based chinese board, controller and drivers in one type of board, bi-polar setup with no microstepping configured. 24V supply. The steppers are 2.5 A, 1.8 Deg/Step (200 step), 280 Oz.
The problem I'm having is that if I set the velocity max in StepConf such that the pulse rate at max speed is more than 1000 Hz, the motors stall with a high pitched whine, like the magnetic pulses got out of sync and the motor just buzzes, no rotation. This works out to 0.9 in/sec in the XY axis, and 0.4 in/sec in the Z. Acceleration seems to have no effect. At the slower speeds, the machine has a ton of torque, I can't stall the motors easily by pushing on the gantry while it moves.
I did a search on the TB6560 and found some posts regarding modifying the Step Time, Step Space, Direction Hold, and direction setup, but changing these values seemed to have zero effect on the problem.
Questions - would adding microstepping improve a problem like this or not? I wasn't planning on having it, but I think the motors are powerful enough that I could manage 1/2 microstepping. Is this a parallel port issue? It just doesn't seem like it to me.
Thanks.
- Rifraf
I've got a Probotix V90 with a driver and steppers from A Quick CNC. The driver is a TB6560 based chinese board, controller and drivers in one type of board, bi-polar setup with no microstepping configured. 24V supply. The steppers are 2.5 A, 1.8 Deg/Step (200 step), 280 Oz.
The problem I'm having is that if I set the velocity max in StepConf such that the pulse rate at max speed is more than 1000 Hz, the motors stall with a high pitched whine, like the magnetic pulses got out of sync and the motor just buzzes, no rotation. This works out to 0.9 in/sec in the XY axis, and 0.4 in/sec in the Z. Acceleration seems to have no effect. At the slower speeds, the machine has a ton of torque, I can't stall the motors easily by pushing on the gantry while it moves.
I did a search on the TB6560 and found some posts regarding modifying the Step Time, Step Space, Direction Hold, and direction setup, but changing these values seemed to have zero effect on the problem.
Questions - would adding microstepping improve a problem like this or not? I wasn't planning on having it, but I think the motors are powerful enough that I could manage 1/2 microstepping. Is this a parallel port issue? It just doesn't seem like it to me.
Thanks.
- Rifraf
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22 Nov 2012 17:13 #26862
by Rick G
This often just means you are trying to run the steppers faster than they can handle with the voltage and amps available.
Steppers motors have great torque at holding (0 rpm) but after a certain rpm it drops off very quickly.
Micro stepping may make them run smother at slow speeds with some loss of torque but will not help with higher rpm.
Rick G
Replied by Rick G on topic Problem driving Steppers - problem with TB6560?
the motors stall with a high pitched whine,
This often just means you are trying to run the steppers faster than they can handle with the voltage and amps available.
Steppers motors have great torque at holding (0 rpm) but after a certain rpm it drops off very quickly.
Micro stepping may make them run smother at slow speeds with some loss of torque but will not help with higher rpm.
Rick G
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22 Nov 2012 19:21 #26863
by cncbasher
Replied by cncbasher on topic Problem driving Steppers - problem with TB6560?
your running faster than the board can handle as Rick mentions , slow it all down , and work up , rather than try and get the max
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22 Nov 2012 20:33 - 22 Nov 2012 20:39 #26864
by andypugh
Steppers do that. The problem is the inductance of the windings.
V = L dT/dt.
2.5A @ 1000Hz gives us an approximate dI/dt of approx 5000.
A 280Oz-in stepper I found on the Gecko site had a 3.6mH inductance.
That has a back-emf of 24V at 1.3kHz/2.5A.
It isn't that simple, as clearly the current falls off and dI/dt falls off. But any stepper will reach a point where the only way to go faster is to use a higher voltage (and you can't go much higher with the TB6560)
If the motor can be re-wired in parallel then you might find you get a flatter torque curve (the static torque will be lower, but the drop-off might be such that you can go quite a lot faster)
There is rather a complex relationship and trade-off between stepper motor size, gearing and voltage.
The step timing has absolutely no effect. if the driver sees the step pulses, then that is all there is to it.
You might well find that microstepping helps a bit by reducing the di/dt term. There is no harm in trying it, and you sound to have plenty of step-rate headroom.
Make sure that the driver board is powered down before moving the jumpers. Never even think about disconnecting a motor with the board powered up (the TB6560 hates that.)
Replied by andypugh on topic Problem driving Steppers - problem with TB6560?
The problem I'm having is that if I set the velocity max in StepConf such that the pulse rate at max speed is more than 1000 Hz, the motors stall with a high pitched whine
Steppers do that. The problem is the inductance of the windings.
V = L dT/dt.
2.5A @ 1000Hz gives us an approximate dI/dt of approx 5000.
A 280Oz-in stepper I found on the Gecko site had a 3.6mH inductance.
That has a back-emf of 24V at 1.3kHz/2.5A.
It isn't that simple, as clearly the current falls off and dI/dt falls off. But any stepper will reach a point where the only way to go faster is to use a higher voltage (and you can't go much higher with the TB6560)
If the motor can be re-wired in parallel then you might find you get a flatter torque curve (the static torque will be lower, but the drop-off might be such that you can go quite a lot faster)
There is rather a complex relationship and trade-off between stepper motor size, gearing and voltage.
The step timing has absolutely no effect. if the driver sees the step pulses, then that is all there is to it.
You might well find that microstepping helps a bit by reducing the di/dt term. There is no harm in trying it, and you sound to have plenty of step-rate headroom.
Make sure that the driver board is powered down before moving the jumpers. Never even think about disconnecting a motor with the board powered up (the TB6560 hates that.)
Last edit: 22 Nov 2012 20:39 by andypugh.
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23 Nov 2012 13:18 #26872
by rifraf650
Replied by rifraf650 on topic Problem driving Steppers - problem with TB6560?
I set the micro stepping to 1/2 and was able to get the machine to run smoothly at 1.6 in/s (96 in/min). This is around 3Khz max pulse rate. This should be plenty enough for this little machine. The motors are running much smoother and quieter in this configuration.
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23 Nov 2012 14:00 #26873
by Rick G
Replied by Rick G on topic Problem driving Steppers - problem with TB6560?
Glad to hear you are getting it sorted out.
After you find the max speed and max acceleration for your machine I always back off from these settings to maintain a safety margin.
Rick G
After you find the max speed and max acceleration for your machine I always back off from these settings to maintain a safety margin.
Rick G
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