DC Stepper motor stall  

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JJ2013
(@jj2013)
Active Member
Joined: 1 month ago
Posts: 16
2019-10-13 9:51 pm  

Hi,

As I wrote previously,  I am using a DC Stepper Motor to bring to resonance a transmitting magnetic loop antenna.  Many of my peers use regular DC motors with either planetary gears or gear-reduction drives.  My system has a DC Stepper Motor that I control over WiFi as it is very convenient to do it that way.  However, I am having issues with the motor "stalling" quite often.  This platform (not of my design) issues "flags" of different types and is helpful.  I am not sure why I am getting this "stall" though.  

The motor is mated with the shaft of a vacuum variable capacitor (VVC) using a flexible,  non-conductive coupler which is important due to the radio-frequency (RF) power level involved.  Up to 600 W at 7 MHz.  The VVC is coupled in series with the loop.

The "stall" can be seen in the GUI and also observed as the resonant frequency of the antenna does not change.  The GUI shows the angular position of the shaft of the motor and also the "handle" by which I rotate the shaft and when the stall occurs, I can see the handle having moved by the number of degrees that I had chosen with the shaft of the motor having stayed put.   

There is an array of pretty sophisticated parameters that can be adjusted and it may be that I have have a mistake there,  but the fact that the "handle" had moved but the motor not tells me that the command went through.   Also, initially I thought that perhaps the distance from the antenna (out in the back-yard) to where my transmitter is too long at about 50 feet. 

Any thoughts and/or suggestions would be welcome!

 

Best!!

 

Juha

 

P.S.  I have also contacted the designer of the control system for additional information and suggestions.

 

 

 


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Altoidian
(@altoidian)
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Joined: 5 months ago
Posts: 16
2019-10-14 3:19 am  

What are the specs on the stepper motor?


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roodyj
(@roodyj)
Active Member
Joined: 2 months ago
Posts: 10
2019-10-14 3:39 pm  

Sounds like we are trying to accomplish the same thing. I am using a GoodRobotics(GR) WiFiStepper controller and a NEMA17  17HS15-0854S stepper. Very new to this, but found that playing around with steps per second, micro stepping value, and other values I could improve the stall characteristics pretty much. I found that current mode worked much better than voltage mode. Here is a copy of my MOTOR config values:

MOTOR.setconfig({
    'mode': "current", 'stepsize': 16,
    'ocd': 500, 'ocdshutdown': True,
    'maxspeed': 260, 'minspeed': 0, 'accel': 250, 'decel': 500,
    'cm_kthold': 0.8, 'cm_ktrun': 0.8, 'cm_ktaccel': 0.8, 'cm_ktdecel': 0.4,
    'fsspeed': 260, 'fsboost': False,
    'cm_switchperiod': 44, 'cm_predict': True,
    'cm_minon': 21, 'cm_minoff': 21, 'cm_fastoff': 4, 'cm_faststep': 20,
    'reverse': False, 'save': True
})

 Hope this helps you a bit.

Also, I am writing a Python 2.7 GUI based on the GR code snippets, but I can't get the 'methods' to work within my 'def' modules. 

Jim


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JJ2013
(@jj2013)
Active Member
Joined: 1 month ago
Posts: 16
2019-10-14 6:24 pm  

Hello "Altoidian,"

Thanks for come-back.

I used the link to the motor that the maker of the platform emailed,  but it doesn't return any results any more.  Using a NEMA 17 bipolar, 59 ncm-84 ozin 2A stepper motor.  I don't have the torque that my application calls for but it is rather low a figure.

I am a complete tyro when it comes to DC steppers and I really should read up on them to better understand basic characteristics.  The maker suggested that adjust "The percentage of input voltage to drive the stepper motor when commanded to accelerate rotational speed" ....an array of parameters to adjust (if one knows what one is doing which I don't as of now).  

Not much of an "answer" I am afraid.

Best!

Juha

 

 

 

 


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JJ2013
(@jj2013)
Active Member
Joined: 1 month ago
Posts: 16
2019-10-14 9:25 pm  

@roodyj

Hi Jim,

I sure appreciate the come-back.  I have made some adjustments to parameters.  Still get a Stall flag,  but no over-current flag.  Some progress.

I need constant speed really and low accel/decel numbers.  Torque is really quite low.

It seems that I had posted this in the wrong place.  Under "Itroduction."

Thanks!

 

Juha

 


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roodyj
(@roodyj)
Active Member
Joined: 2 months ago
Posts: 10
2019-10-14 11:58 pm  

@jj2013

No problem, Juha. I was wondering if you are doing your development in Python and is your controller from GoodRobotics? If so, I would appreciate sharing details of what works or doesn't. Having a tough time here getting MOTOR commands to respond to button-clicks.

Regards, Jim


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JJ2013
(@jj2013)
Active Member
Joined: 1 month ago
Posts: 16
2019-10-15 6:52 pm  

@roodyj

Jim,

Yes, I am using the GR controller.  To issue commands I use my Android smartphone as my lap-top is dedicated to processing of audio in the digital domain.  By audio I mean audio that I am transmitting over the air (7 MHz).  No issues to get commands to execute, but I am still having a "Stall" flag come up without fail, every time.  The maker has been very patient with me and emailed parameter suggestions.  Using "Servo" in Voltage Control mode right now.  Don't need a lot of torque and constant (very low speed) are all that the application calls for.

I wanted to control the WiFi stepper using my lap-top as the display is much larger,  but I am having a tough time getting the lap-top to communicate with the stepper.  Firewall and Anti-virus related I would imagine so I need to figure it out.

I have also changed the frequency of the PWM scheme too,  but I am not clear on if that would impact the point at which stalls occur?  Also, the frequency is rather critical as I will hear a lot of "hash" (EMI) on my receiver (although I have used ferrite toroids of a Mix that is to cut down on the EMI level at 7 MHz).

A whole galaxy of parameters that one can adjust and get one into trouble unless one knows what one is doing.  Clearly, my knowledge in DC stepper motors is poor and I am not able to get rid of the stalls.  I am finding that the Voltage Mode works better for me.

 

Juha

 

 

 

 


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