Stepper motor sizing based on load travel time and distance

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Dan Pressman

Joined Apr 19, 2017
10
Hello, I am a software guy who is new to using stepper motors. Basically I have built a large moving bookcase door that rolls back and forth. I have connected it to steel cables and pulleys into the attic where I want to place a stepper motor and gearing to open and close the door. I had imagined using a chain drive attached to the steel cables. Size is not a problem as all of the mechanics are up in the attic.

I am not sure where to start and do not expect you to all my work for me but could you at least point me in the right direction?

Here is what the operational parameters are:

Distance of travel: 40 inches

Force to roll Bookcase: 25 lbs (measured by pushing on a scale against the bookcase) Actually it was probably closer to 30 to get movement started and 18 while moving.

Expected time of Travel: about 3 seconds maybe more

Frequency of usage: No more than 45 times a day

Why a stepper? This "Bookcase" will actually contain some fairly fragile artwork - sculptures etc. so i want to be able to accellerate and decelerate smoothly. I plan to use ultrasonic distance measurers to confirm the position as there is some slack in the cables and I would expect some stretch. Obviously exact positionoing is really only important at the beginning and end of the motion. I will also use infrared motion detectors to check for obstacles (either stationary or moving - think scurring dogs trying to beat the door).

I can gear the motor as needed as there is no problem with space.

I plan to use either an arduino or a rasberry pi to control the door.

I would prefer the motor to be unbraked (?) so it can be moved manually if needed.

I have attached a picture of the 8 ft tall bookcase (before the finish moldings and shelf lighting were installed) and two pictures of the mechanism as it attaches to the bookcase and guide track and of the cables going up to the attic. There is a second guidebar and attachment at the bottom as well as cables to pull the bookcase both open and shut.


Thank You VERY much!
 

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MaxHeadRoom

Joined Jul 18, 2013
21,402
First you need to calculate or measure by some means the actual torque required to move the load.
There are a few ways this can be done.
You will aslo need a suitable stepper driver and power supply.
A stepper motor has holding torque when powered or (less) intent torque when non-powered.
I suggest a visit to stepper sites such a Gecko steppers for some sizing info.
Max.
 
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