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    Default Need help selecting stepper motor

    I have constructed an 8ft tall moving bookcase/hidden door that rolls on wheels on a cement floor. I have already constructed guide rails that keep it from "walking" in and out. I have connected steel cables to the top and bottom - one set to pull open and one set to pull close. With pulleys I have directed these two pairs of cables to a common point (in the attic) where I plan to mount the motor. The cables come straight up vertically to the motor position. My though was to use chain on the motor and connect the cables to the end of that chain (I have attached turnbuckles to the cables to enable adjustment).

    As I said I have already constructed this and using a pulley and weights in place of the motor have measured that it takes 32lbs to move the door in each direction. The door travel is about 46-48 inches. I would think I would like it to open in about 3 seconds. As this bookcase will have some fragile things on it I would like it to start slow and accelerate.

    So while I am a newbie at this I am a software guy who has an EE degree from 40 years ago so I can handle the math but I need some help on where to start. I have tried a few stepper sizing programs and it seems that a belt drive with a 90 degree orientation makes the most sense. But...

    I am not sure how to decide on direct or geared drive etc, Where should I start?

    Thank you in advance.

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    Default Re: Need help selecting stepper motor

    Definitely a linear actuator would be a great fit for this application. Most have built in limit switches, are lead screws so they can push a lot of force. It's easy. They aren't as great for incremental positioning but probably doesn't matter for you.

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    Default Re: Need help selecting stepper motor

    Can I accelerate and decellerate???



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    Default Re: Need help selecting stepper motor

    Small inexpensive garage door opener.

    Retired Master Electrician, HVAC/R Commercial union shop and Lots of hobbies. FLA Saturn 2 4x4 CNC Router


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    Default Re: Need help selecting stepper motor

    I had thought of that and actually have an old garage door opener lying around. Can I accelerate and decelerate using an arduino somehow?



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    Default Re: Need help selecting stepper motor

    Quote Originally Posted by DPress2 View Post
    I had thought of that and actually have an old garage door opener lying around. Can I accelerate and decelerate using an arduino somehow?
    No I doubt it, why do you want two speeds? You can change the sprocket to slow it down, and use the limits installed. The newer ones have LED's to keep it from moving if something blocks the door.

    Get a 12 VDC linear actuator. They move very slowly. Surplus Center out in Nebraska usually has a few different kinds.

    Retired Master Electrician, HVAC/R Commercial union shop and Lots of hobbies. FLA Saturn 2 4x4 CNC Router


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    Default Re: Need help selecting stepper motor

    I want to be able to start slow and build up speed so things in bookcase do not get jostled.



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    Default Re: Need help selecting stepper motor

    Not sure how you can start slow, speed up, and slow down, while moving 4 ft, in 3 seconds??


    Where should I start?
    Figure out how fast the motor needs to turn, and how much torque you'll need at that speed to move 32 lbs. You'll likely need enough force to move at least 50 lbs, as accelerating takes a lot more force.

    A PLC might be a good choice to control it.

    Gerry

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    Default Re: Need help selecting stepper motor

    Quote Originally Posted by DPress2 View Post
    Can I accelerate and decellerate???
    Well, you're going to have to figure stuff out on your own no matter what solution you choose, I'm sorry to say. With a linear actuator, you won't need limit switches or any gearboxes, etc. But yeah, you'll have to rig some PWM accel/decel thing with mosfets or whatever. They just have basic DC motors in them (mostly), so ramping up and down the voltage should be a fix.

    If you just want to throw money at it and figure out less, I'd buy a Clearpath Servo. They have built in positioning as well as accell/decel and are super torquey. But the servo itself is like $300+, plus a DC power supply.



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    Default Re: Need help selecting stepper motor

    Getting it to accelerate smoothly at the start is easy, just pick an actuator with only a bit more force than needed to move it, the extra force goes towards acceleration. Of course this has the downside of if the friction goes up a bit, it'll stall. Doing a PWM or voltage ramp at the start is fairly easy as well.
    More difficult is getting it to stop smoothly. I assume it has to stop at a specific location? Something with an encoder or a stepper will be necessary to really make it decelerate smoothly to a stop right where you want it. Less elegant it to have it run at full speed for a short time, then just drop the PWM after a time or a "near closed" limit switch and try to get it so it doesn't stop too abruptly.



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Need help selecting stepper motor

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