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changing jerk to acceleration?

Discussion in 'CNC Mills/Routers' started by don price, Nov 28, 2019.

  1. don price

    don price New
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    I'm in the process of switching over from a tinyG controller to the Black Box for my SMW3D R7 which is similar to the Lead 1010 except for using an 800W spindle rather than a router. I changed the default values for max travel and max speed to better match the recommended R7 values. The machine runs fine except it is noticebly slower at acceleration and deceleration. Not a big deal for longer straight cuts painfully slow (as in MDF on fire slow) for curvy detail work.

    The BB X & Y acceleration is currently set for 10 mm/sec^2. The tinyG x (and y) jerk maximum (xjm and yjm) was set for 10,000 mm/min^3 * 1 million. I'm a little lost since jerk is the derivative of acceleration so I figured I should ask for input before just turning up the acceleration to 50 and watching what happens.

    Thanks!
     
  2. Gary Caruso

    Gary Caruso OpenBuilds Team
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    Hi Don, Turn it up past 50! something like 500 even, experiment with what works best for you.
    Personally I have something like 600 on Y and Y and 400 on the Z.
    Run a simple program cutting air and see how it looks and sounds.
    Cheers
    Gary
     
  3. David the swarfer

    David the swarfer OpenBuilds Team
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    max speed and max acceleration are a balancing act.
    you can get insane max speed at the cost of lower acceleration.
    or insane acceleration at the cost of max speed.
    (all because of the torque curve of stepper motors)

    My method is to just guess the 2 values, fairly low. ie max speed is not scaring me and acceleration is taking about 1 second to get to max speed (you can hear it). now I double acceleration until it takes about 0.25 of a second.

    with that done I start to double the max speed until it stalls during acceleration, then go back to half way between the value that worked and the one that stalled. that will probably be reliable. but do test with full axis travel,.... (max speed tests are all G0 moves, all cutting will be (G1 moves) slower unless you are cutting foam)

    on my Ox I got up to 7500mm/min which worked just fine except in one sticky spot on the X access. Had to slow it down to 3500mm/min for reliability until I get around to stripping the machine to fix that spot (Z has to come off to get to it). This will probably happen when I change the Z from Ox style to Sphinx style.

    PS: this doubling and halving the difference is known as a binary search in Computer Science, the fastest way to find an item in a sorted list.
     
  4. don price

    don price New
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    Thanks guys! I bumbed it up to 250 and it is much more responsive.
     
  5. Gary Caruso

    Gary Caruso OpenBuilds Team
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    Keep going! ;)
    Cheers
     
    Peter Van Der Walt likes this.
  6. Peter Van Der Walt

    Peter Van Der Walt OpenBuilds Team
    Staff Member Moderator Resident Builder Project Maker Builder

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    You can borrow the Lead1010 profile in OpenBuilds-CONTROL then
    See OpenBuilds/OpenBuilds-CONTROL (source code of the profile, if you are using OpenBuildsCONTROL from software.openbuilds.com -> grbl settings -> select the Lead 1010)
     

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