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Soft start dc motor controller

Discussion in 'Robotics & Mechatronics' started by Loupy31, Jun 24, 2015.

  1. Loupy31

    Loupy31 New Member

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    Hi All,

    I am looking to build a dc motor controller for a model ski lift. at present it only has an "On Off" switch, I would like it to include a soft start, reverse and half speed switches (push button type).
    The motor drags about .6 amp and is a 6 volt dc type.
    The idea is to give the model full automation and realisim,

    any help would be great

    Peter
     
  2. Tony Stewart

    Tony Stewart Well-Known Member Most Helpful Member

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    Current limiter will also limit torque which limits acceleration. Then voltage limit will limit speed. Starting stiction and rolling friction are unknowns which , if excessive , may pose some hysteresis around desired smooth acceleration control which is best obtained with a velocity sensor and acceleration & speed profile in memory and controlled by PWM in a loop. You could get a bunch of metal Oxide current limiters and gang them in parallel or use 50 mV/A current shunt with adjustable comparator to choose the current limit you want and drive the voltage with a full bridge at 0, 5V,9V, -5, -9 limited by 0.4A, 0.5A,0.6A, 0,7A with full power surge start current expected at 5x normal or >3A
     
    Last edited: Jun 27, 2015
  3. KeepItSimpleStupid

    KeepItSimpleStupid Well-Known Member Most Helpful Member

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    This http://www.jameco.com/webapp/wcs/stores/servlet/Product_10001_10001_120539_-1 kit has a slight amount of soft-start available. I used it to drive a shutter. It is noticeable, but I don;t know the time frame.

    If nothing else it gives you speed control out of the box and it might be able to set two speeds using two pots and a slight circuit modification.

    If you implement dynamic braking, you can have fast stops. One method is to short the motor when commanded to stop.

    "H-bridges" like the L298 is available in many kits. They can reverse and drive the motor directly.
    Usually they use Direction and "Not enable" as control signals. A carryover to when TTL floated high.

    Some drivers offer coast, brake, fwd and reverse.

    Any method you choose will have it's own constraints and upgrade paths.

    I'd suggest looking at www.picaxe.com. So, this http://www.canakit.com/catalogsearch/result/?q=uk1122&x=0&y=0 and a PICaxe, a logic supply and some glue logic.

    Reversing can be done with a single relay as well, so the PWM kit and it's built-in soft start can become a start.

    You can modify the PWM kit to drive the H-bridge. So, now Analog control (0-5V) can be used to control speed.

    Later, you can use use the PICAXE to both control speed, acceleration and direction to the L298 driver.
     

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