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Thread: stepper-control-with-acceleration

  1. #31
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    I would start by not just getting the hardware done and as hippy suggests with figuring out how fast you need the motor to go. You are going to need to know the diameter of the drive wheel and the gear ratio (if you used gear) to calculate the speed that the motor need to turn.

    if the wheel is 8cm in diameter, you would need 4 turns per second (for 1m/s), or 800hz pulse with direct drive - this is, as shown by Circuit is achievable with toggle option.

    while it seems great to use code that others have written and are known to work, unless you understand them completely and have taken into the account of the application of the system you will most likely be better off starting from scratch - its s great way to learn.

  2. #32

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    Hi,
    I need 1700 Hz for motor input. Surely the motor without the cariage will start with that freq. But the inertia of the cariage and the load might make that the the motor is stalling at startup. That is why I need to build the thing to test. At the end it might work wihout ramp up but I doubt it.
    Concernig making ing the program, you are both right to start a program from scratch and make it to wath I need. But my programskils are verry small.
    Thank you all,
    Willy

  3. #33
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    Quote Originally Posted by Satchid View Post
    Hi,
    I need 1700 Hz for motor input. Surely the motor without the cariage will start with that freq. But the inertia of the cariage and the load might make that the the motor is stalling at startup. That is why I need to build the thing to test. At the end it might work wihout ramp up but I doubt it.
    Concernig making ing the program, you are both right to start a program from scratch and make it to wath I need. But my programskils are verry small.
    Thank you all,
    Willy
    Let's make the maths easier, and assume you need 1600 steps per second (rather than 1700). A typical 200 steps per revolution stepper, (1.8 degree per step), driven by the appropriate chip which provides the required H-bridge actuation at each "step" pulse, would require 200 pulses to complete a full revolution. At 1600 pulses per second, that would be 1600/200=8 revolutions per second, or 480 RPM (revolutions per minute). Very few stepper motors will leap to this speed instantaneously.

    If you are microstepping, the motor driver chip would require faster step pulses to maintain the same speed. If you require 1/32 microstepping, the driver chip would require 200*32=6400 step per second pulses to drive the motor at the same 480 revolutions per minute. Very, very, very few stepper motors will leap to this speed instantaneously.

    A common misunderstanding is that folks assume that steppers are voltage driven. They are not. They are current driven. Which is why stepper driver chips take control of the motor current, and prefer very high (10-100 volts) motor supply voltage. The driver chip determines when the motor inductance has received enough current to make the step; in general, the higher the motor voltage, the better (faster stepping, within the driver's voltage limits).

  4. #34

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    The 1700 pulses are already calculated including 16 u-steps.

    Thanks,
    W

  5. #35
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    Quote Originally Posted by oracacle View Post
    if the wheel is 8cm in diameter, you would need 4 turns per second (for 1m/s), or 800hz pulse with direct drive
    I agree with your maths, but the speed required is 1 metre per minute, not 1 metre per second, so a stepping rate for a directly coupled stepper of about 14 steps per second.

    If there were 100:1 gearing that would require some 1400 steps per second with about 0.00005 mm travel per step.

    It seems that the gearing could be reduced from 100:1 to make the stepping rate more manageable.

  6. #36
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    my bad, dunno where I got that from. Surprised it wasn't noticed sooner.

  7. #37
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    Hippy said in a previous thread that you apply pulses and "they fly". I never figured them using cheap unipolar motor/gearboxes from ebay and the info provided by forum users who know how to use them makes it seem even more complicate,well to me. You'd think if you send a pulse to the say 4 pins so the coils are energised in the sequence that makes the rotor turn to next position then the next pulse quicker up to a maximum frequency of pulses in order to the pins as needed for full or half wave then a maximum is achieved. Indeed I got to 140Hz and the motor stood still and whined. As erco said.like his ex. Get it turning then speed it up. I hate them. Good luck. How do you keep them going...don't mention that.

  8. #38

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    Hi All, I want to thank all af you that tryed to help me!
    I am abandon the picaxe in this in favor of a old standard pc with windows xp or something use mach3 to drive the dolly only for the driving.
    I will use the "x" axis. there I can program the speed and distanses to accellerat and desellerate easilly.

    I can not do that for the steering that I asked about in http://www.picaxeforum.co.uk/showthr...-black-line-lt .

    But, and specially from Hippy I learned allot . It is not allways easy because a 73Year old brain is not as flexible anymore, and de lanuige is not as aesy as my own, but I learn.

    Gratefull,
    Willy

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