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How should I decay? What's the best mode for me and my stepper motor controller — Parallax Forums

How should I decay? What's the best mode for me and my stepper motor controller

ElectricAyeElectricAye Posts: 4,561
edited 2010-04-13 20:07 in General Discussion
I'm working with the L6208 bipolar stepper motor controller chip and it has an option for adjusting the behavior of its inbuilt bridge circuit. (See page 14 on attached datasheet.) I have no clue why somebody would chose one decay mode over another so I thought I'd consult the forum for insight.

Why would you select one mode over another? Is it a matter of speed? or some combination of speed and current? I haven't tested the system yet and I thought I'd ask before I do something stupid.

thanks,
Mark
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Comments

  • James NewmanJames Newman Posts: 133
    edited 2010-04-13 18:13
    In fast decay mode you allow current from the motor to go directly to the psu. This allows the magnetic field to collapse quickly. The motor will coast afterwards. The advantage will manifest as faster possible motor speeds.

    In slow decay mode you feed the current from the motor back into itself. The magnetic field collapses slowly in this case. The motor will 'dynamically' brake. This is sometimes a desirable attribute, but it will limit the motors speed.
  • ElectricAyeElectricAye Posts: 4,561
    edited 2010-04-13 18:23
    James Newman said...
    In fast decay mode you allow current from the motor to go directly to the psu. This allows the magnetic field to collapse quickly. The motor will coast afterwards. The advantage will manifest as faster possible motor speeds.

    In slow decay mode you feed the current from the motor back into itself. The magnetic field collapses slowly in this case. The motor will 'dynamically' brake. This is sometimes a desirable attribute, but it will limit the motors speed.

    James,

    I've been playing with this feature today and I noticed that in 'fast decay' the operation of the motor seemed more "crisp" and yet a bit too noisy for my liking. In "slow decay" it provides me with plenty of speed for my application yet seems smoother and quieter when stopping. I just didn't know why it was behaving so differently, but your explanation of the dynamic braking makes a lot of sense now. Suddenly I almost feel like I know what I'm doing with this thing. lol.gif

    Thanks very much for explaining this to me!
    Mark
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  • davejamesdavejames Posts: 4,047
    edited 2010-04-13 20:07
    James Newman - LTXC?

    DJ

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