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GRBL Acceleration Rates

Discussion in 'Motors' started by Ronald4418, Jan 22, 2021.

  1. Ronald4418

    Ronald4418 Well-Known
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    Am I only scratching the surface with my Setup and am I capable of much more. Currently I have $120 and $121 set at 3,600 along with $122 set at 2600. I was trying the most advanced speeds that I felt safe with as I never even came close to stalling out my motors. Is it worth increasing to the point of Stalling Out my motors and then backing off until they aren't followed by making the setting 80% of that number?
     
  2. Giarc

    Giarc OpenBuilds Team
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    That is what I did.
     
  3. kevinbaileycrum

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    In same boat as well trying to find ways to get max speed out of my motors. I think the challenge is finding a good acceleration rate because with a given max speed value s it still takes time t to get to that speed and my machine isnt large enough to allow to allow a movement to be accelerating for t in order to reach s.
    I heard grbl has plans to work on increased 'rapid acceleration' type movements in their github
    "we intend to research and implement more-advanced motion control algorithms, which are usually reserved for machines only with very high feed rates (i.e. pick-and-place) or in production environments"
    Im excited for that. Additionally someone recommended on stack overflow the book "Stepping Motors: A guide to theory and practice" namely chapter 5 as it discusses higher speed operation.

    hope that helps, if you are able to get massive acceleration and speed tuning let us know!!!
     
  4. David the swarfer

    David the swarfer OpenBuilds Team
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    You have to achieve a balance between max speed and acceleration
    You can achieve very high max speeds with visibly slow acceleration
    You can achieve almost instant acceleration, with very slow max speed.

    The problem with high acceleration is jerk, the entire machine will deform due to the inertia, and this will affect surface finish and accuracy.
    So, you have to decide what suites you and your machine. I had my OX at 7500mm/min and about 2000mm/s/s but it shook the whole table and left marks in the edges of parts (it also got stuck at the slightest sticky spot on the wheels), so I slowed it down to 4500mm/min and about 1000mm/s/s and it and I are much happier (-:
     
  5. kevinbaileycrum

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    Hey @David the swarfer ,

    Out of curiosity when you say "You can achieve almost instant acceleration, with very slow max speed."
    are you saying :
    - instant acceleration because with a low max speed you are able to reach said speed very quickly hence acceleration seems instantaneous ​
    or:
    - the acceleration / accelration rate is actually much higher on a motor control system that has a low max speed​
     
  6. David the swarfer

    David the swarfer OpenBuilds Team
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    The 2nd one. with a low max speed you can actually set the acceleration very high, much higher than if the max speed were at a 'useful' level.
    This situation is not actually useful, well I suppose there is a machine somewhere that could use it, but the knowledge that it is possible, that max speed and max acceleration are related and need to be balanced for the application, is useful to everyone setting up a machine. If you need the ultimate in max speed you are going to have to trade acceleration to get it. Experience suggests that you want a more balanced setup, machines work better when they are not working too hard.
     

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