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DRV8824 Direction change on the fly

sunish nair
Prodigy 60 points
Other Parts Discussed in Thread: DRV8824

hi all

we are designing a stepper motor controller, using DRV8824

my question is is it possible to change the direction on the fly?

what all should take care / procedure to do so? 

secondly  how should we define which decay mode is to be used?

how much time will the motor be on hold condition after the drive is enabled?

what defines the motor supply voltage?

the motor supply voltage(VM) is ranged from 8V - 45V and maximum drive current is shown as 1.6A at 24V

so, how can we calculate the drive current in different voltage levels? 

regards

sunish

  • 0
    TI__Mastermind 26065 points

    Hi Sunish

    Please refer to below comments.

    we are designing a stepper motor controller, using DRV8824

    my question is is it possible to change the direction on the fly?

    what all should take care / procedure to do so? 

    The direction control logic is active on the fly. But most stepper cannot response to sudden direction change at above certain speed. Even start up at Zero speed, we need to match the MAX startup speed. So you can imagine shifting the direction we need to apply proper decelerating to zero speed and then accelerating to other direction.

    secondly  how should we define which decay mode is to be used?

    If micro stepping is used, mixed decay will always gives good effect.

    how much time will the motor be on hold condition after the drive is enabled?

    The current will excited immediately tafter enabled. stepper usually hold the position mechanically with in several tens of millisecond. it is depended on the motor and load condition.

    what defines the motor supply voltage?

    Steppers driving with current level. And they will have its named voltage level. But you could drive a 12V stepper motor with 24V VM and the same current level setting. Higher voltage will give you better high speed running ability.

    the motor supply voltage(VM) is ranged from 8V - 45V and maximum drive current is shown as 1.6A at 24V

    so, how can we calculate the drive current in different voltage levels? 

    We use the same current level in different voltage, which is usually more important to keep the same torque output for applications.

    Thanks.

    Wilson Zuo

    Motor ApplicationTeam

  • 0 in reply to Wilson Zuo
    Prodigy 60 points

    dear Wilson

    thank you for the reply

    are the micro step selection pins can also change on the fly?

    The current will excited immediately after enabled. stepper usually hold the position mechanically with in several tens of millisecond. it is depended on the motor and load condition.

    i came to know that some drives will release the motor if there's no step pulses received for certain time.does the DRV8824 follow the same ? or it will hold the motor until  the drive is disabled?

    regards

    sunish

  • 0 in reply to sunish nair
    TI__Mastermind 26065 points

    Dear Sunish

    The micro step selection function is logically change on the fly. But we don't recommend to do so in stepper application, because it is equivalent to change the motor speed immediately. Stepper may not able to response and step missing or even stop will happen.

    Steppers works in the way that the current is always there no matter running or stop untill you disable the driver. One important reason is that the application need the motor to keep the holding torque during stop or paused condition. Also it is a common method to lower the current and power consumption but still keep certain holding torque by lower the current to 50% or other value during stop state. You can achieve this by change the Vref or current level settings.

    Thanks.

    Wilson

  • 0 in reply to Wilson Zuo
    Prodigy 60 points

    Dear Wilson

     

    thank you for the reply.

    i am not intended to change the microstep function on the fly. the question was just to confirm.i will certainly provide enough time for the motor to complete the present operation.

     

    regards

     

    sunish