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DC Stepper Motor stalls

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(@jj2013)
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All,

As I wrote previously (by error,  I posted all this where I was supposed to Introduce myself) ,  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. 

Been playing around with several parameters and am making some progress.  My application does not really call for a lot of rotational speed,  but accuracy is important. That way I will be in the "ball-park" and am close to having a resonant antenna based on the rotational angle and direction that I have the shaft of the stepper motor at.

Any thoughts and/or suggestions would be welcome!   "Altoidian" and "Jim" already kindly responded 🙂

 

Best!!

 

Juha

 

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


   
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byron
(@byron)
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Hi  @JJ2013,  its really quite hard to envisage your set up from your description but I think you may be alluding to having a program that you run on your computer that has a GUI display and this program uses wifi to to communicate to  another computer or microcontroller to which a stepper motor is attached??   

Well this is just what the dronebot episode 'WiFi Stepper Motor Controller with Web-based Interface" is all about.  Have you perused that article?  


   
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(@jj2013)
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@byron

Hi Byron,

I am using the Good Robotics platform and the Drone Bot video was very helpful in orded to get up and running.  As I wrote in another post I am having a problem with "Stall flags."  I see from the GUI that the shaft of the stepper motor rotates though,  but I need to fix the stall.  The support from maker of the platform has been very good despite my asking some rather elementary questions :-).  Voltage control (Servo mode) seems to be more "stable" in my case,  but I am still getting those flags......There is a whole host of parameters that one can adjust to get rid of the stalls,  but I am not there yet.  My knowledge of DC steppers isn't very deep and it shows.

Not sure but I think that selection of the frequency of PWM pulsing might also impact the current/voltage that the stepper needs for a given torque.  My thought process is that the higher the PWM frequency the lower the power required for a given torque but this may be completely off base.

Best!

Juha

 

 

 


   
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(@roodyj)
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Posted by: @byron

Hi  @JJ2013,  its really quite hard to envisage your set up from your description but I think you may be alluding to having a program that you run on your computer that has a GUI display and this program uses wifi to to communicate to  another computer or microcontroller to which a stepper motor is attached??   

Well this is just what the dronebot episode 'WiFi Stepper Motor Controller with Web-based Interface" is all about.  Have you perused that article?  

Hi Byron. I've watched that tutorial many times, and in fact, that is what pointed me to obtain that WifiStepper unit. I am working on the same functionality that @JJ2013 is: tuning app with vacuum variable capacitor. The problem I have is that the Dronebot tutorial was not done in Python scripting, and that is what I am using.  If you can point the way to a functioning Python script demo for the WifiStepper, I would be very grateful.

 

Best to you,

Jim 


   
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byron
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Hi @roodyj - I hesitate to send this link as I'm presuming you must be aware of it, but just in case 

https://www.wifistepper.com/interfaces/python.html.

and of course their github has the python libraries and an example test.py

Are you saying their examples don't work or you are looking for a more in depth program

I've not used the WifiStepper controller board.  I have used the Diablo controller board from PiBorg and they have example python programs for controlling their board that work OK though thats not really any help for you I'm afraid.

 

 

 


   
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Spyder
(@spyder)
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Posted by: @jj2013

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. 

Ya know, many many years ago I was playing around with an antenna in my back yard, and I decided to put a light at the end of the wire where the antenna was, a little over 50 feet away. It was just a flashlight bulb that regularly takes 2 AA batteries, so I figured that those same 2 AA batteries should be fine

So I hooked those 2 AA batteries up to the end of the wire that was inside my house, and flipped the switch...

And nothing happened

I checked it and checked it, and everything was fine, but that light just refused to light up

Until I hooked up 3 D cells to it. Then it worked fine

Tesla was right, and Edison was wrong. You can't run DC over long wires real well


   
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robotBuilder
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Posted by: @spyder

Tesla was right, and Edison was wrong. You can't run DC over long wires real well

Are you sure?  Isn't it about using high voltages vs. low voltages? The advantage of ac is the ability to easily convert between the two using transformers.

 


   
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(@jj2013)
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@roodyj

Jim,

The stepper works quite well in that I am able to tune a mag loop antenna.  The only issue is the "Stall flags."  Just need to adjust parameters to get rid of the "stall."  The shaft of the VVC rotates (as evidenced by my antenna analyzer that provides a chart on  VSWR per frequency) so I guess the stall isn't that serious,  but I still want to rid myself of any such flags.  Servo in Voltage Mode is what I have settled on for now.

A screen capture would get you the Python,  but it is also something that sort of works for my VVC and would likely be a complete waste of your time.

Best!

Juha

 


   
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Spyder
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Posted by: @casey

Isn't it about using high voltages vs. low voltages? The advantage of ac is the ability to easily convert between the two using transformers.

Exactly. The reason DC wouldn't work was because the drop was too severe. "The D.C. system of power distribution however was flawed, in that, like with Wm. F.Cooke's initial telegraph electrical signal transmission experiments, the signal strength diminished over long distances. "

https://ethw.org/Edison%27s_Electric_Light_and_Power_System

My thought is that with so low a power requirement for the antenna motor, it can handle only a much shorter distance, so it's sending the "move" signal, it might even be receiving that signal and acknowledging it, but the power to actually move it might not be there

Just a thought, but, on the other hand, I'm frequently wrong


   
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(@jj2013)
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@spyder

The DC portion of the cable isn't very long, the rest is AC.  And, the same extension cord I use on my hedger without any problems.  Also, the motor is used to rotate the shaft of a vacuum variable capacitor not the actual antenna.  Torque is pretty low really.   I would be surprised that the short run length of the DC portion of the cable is the "culprit."

Thanks.

Juha

 


   
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(@roodyj)
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Posted by: @byron

Hi @roodyj - I hesitate to send this link as I'm presuming you must be aware of it, but just in case 

https://www.wifistepper.com/interfaces/python.html.

 

 

 

Byron,

Thanks for pointing me to the URL above. I have read it and I have also read the GR documentation, and the Python 2.7 documentation, and the PyCharm stuff...

Looking back, I'm certain that my problem is really that I have been trying to learn a lot all at once! "The blind will stumble until they know the layout of the room."

It will be easier for me to learn the "layout" when I find a script that combines the little command snippets of the GR docs into  a truly functional "main.loop" script with labels, buttons, def's, frames, and motor control functions. At this point, I'm not even sure what specific questions I have.

Just gonna take more study on my part, Thanks, all, for any help.

Jim  


   
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(@roodyj)
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Posted by: @jj2013

@roodyj

A screen capture would get you the Python,  but it is also something that sort of works for my VVC and would likely be a complete waste of your time.

 

Juha,

A screen capture would certainly help me. Not a complete waste of time. Please post or send as attachment.

Jim


   
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Spyder
(@spyder)
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@jj2013

Sorry. I misunderstood. I thought that the whole length of the wire was DC


   
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robotBuilder
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Posted by: @casey
Are you sure?  Isn't it about using high voltages vs. low voltages? The advantage of ac is the ability to easily convert between the two using transformers.

What I meant to write was:

The advantage of ac over dc is the ability to easily convert between voltage levels using transformers.

 


   
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(@jj2013)
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@spyder

No worries :-)!

 


   
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