RE: VAL field in Motor record Default unit

["Mooney, Tim M." <mooney@aps.anl.gov>]

Hi Joey,

Yes, there is a hidden relationship between the distance you tell a motor to move and the speed it moves while going there.  The motor ramps up from speed VBAS to speed VELO in the time ACCL seconds.  If ACCL is large enough, the motor won't accelerate to VELO before it's time to start decelerating.

However, that's not what appears to be happening in your video.  I don't understand.  What values are you using for VBAS, VELO, and ACCL?

Tim Mooney (mooney@aps.anl.gov) (630)252-5417
Beamline Controls Group (www.aps.anl.gov)
Advanced Photon Source, Argonne National Lab

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From: Joey Thai [thaij@uw.edu]
Sent: Monday, February 13, 2017 1:01 PM
To: Mooney, Tim M.
Cc: Matt Dentinger; tech-talk@aps.anl.gov; Marissa Elizabeth Kranz
Subject: Re: VAL field in Motor record Default unit

Hi Tim,

I am also a student at the University of Washington working on the same project as Matthew. We greatly appreciated your response and found it consistent with the "Motor Record and related software" documentation provided by this website: http://www.aps.anl.gov/bcda/synApps/motor/R6-9/motorRecord.html

The problem we have is that the VAL field seems to change the speed of the coreless brushed motor's rotation. The YouTube video below demonstrates the speed of the motor when we set the VAL field to 100, then 30:

https://www.youtube.com/watch?v=xR7BVMfGruQ

Notice that the speed of the motor when VAL is set to 30 is noticeable slower than the speed when VAL is set to 100. Since the motor we are using is not using an encoder, the motor does not know its current position. As Matthew said earlier, VAL seems to affect the speed of the motor's rotation.

I guess my question is, is there some sort of hidden relationship between the VAL field and the speed of a motor's rotation?

Best Regards,

Joey Thai

On Sat, Feb 11, 2017 at 11:29 PM, Mooney, Tim M. <mooney@aps.anl.gov> wrote:

Hi Matthew,

The VAL field is the position you want the motor to move to.  You choose the units you want for the VAL field, and then you set the MRES (motor resolution) field to be the distance, in those units, that the motor will move when it's driver gets one step pulse. (You should also set the EGU field to some string that will tell the user what units you chose for the VAL field.  The EGU field isn't used for any other purpose.)

Other background information: the motor's running speed (VELO) is in EGUs per second.  The motor's acceleration time (ACCL) is the number of seconds you want it to take for the motor to get from its base speed (VBAS) to its running speed (VELO). Stepper motors have a resonant speed that you want to avoid.  If you set VBAS to be higher than the resonant speed, the motor will leap immediately to the base speed, avoiding the resonance, and then accelerate from there to the running speed.  This is why short moves are slow, and longer moves are faster.

Tim Mooney (mooney@aps.anl.gov) (630)252-5417
Beamline Controls Group (www.aps.anl.gov)
Advanced Photon Source, Argonne National Lab

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From: tech-talk-bounces@aps.anl.gov [tech-talk-bounces@aps.anl.gov] on behalf of Matt Dentinger [mdentinger43@gmail.com]
Sent: Saturday, February 11, 2017 8:52 PM
To: tech-talk@aps.anl.gov
Subject: VAL field in Motor record Default unit

Dear Tech-Talk,

   Hi, I am a student at the University of Washington and I am learning how to navigate and use EPICS programming.  For the task at hand I will not be able to use encoders, making use of absolute positioning impossible, so I was wondering what default unit the VAL field was in.  Through some testing it seems the larger the value, the faster the motor moves so I guessed that it might be a number that somehow represents revolutions per second (or another given time).  Hope you can shed some light on my issue.  Also, haven't subscribed yet, but I may have to depending on how this project continues.  Thanks again.

  Best,

  
     Matthew Dentinger