- Tue Dec 16, 2014 7:41 pm
#177808
Let's go back to post #1. Correct me if I'm wrong but attached to the motor shaft is a 1.25" diam spool. String winds around that spool an pulls on a 5 lb door. That's a torque on motor of 5 x 16 x 0.75 = 60 oz-in or ~42 n-cm, under the motor spec of 90 n-cm peak. Yet the load may be above the pull-in torque once the motor gets spinning. So you may to slow down the acceleration (keeping the same spindle) or get a beefier motor. W/o knowing the torque curve of the motor I can't say.
http://www.nmbtc.com/step-motors/engine ... ationship/
But there is something of a torque curve at the vendors website. It tells 1/2 of the story.
So, as the OP said, it should work ... if the RPM's are ramped slowly enough and if the driver is really delivering the expected current. Remember that the rotor and spindle have some inertia and take torque to accelerate them.
@ the OP: when you were experimenting w/spindles sizes and accelerations, did you ever find a slow enough ramp so the original spindle worked ? Did you limit the top speed ? Could a slow ramp to a higher max RPM work ?
I note the graph says "half step" but doesn't micro-stepping reduce the motor's torque ? Or have I got it reversed ?
Lastly why not hinge the dog door at it's top and then lock/unlock the bottom, w/appropriate signals to the dog ? Let the dog or gravity do the "heavy lifting" ? No guillotine needed.
http://www.nmbtc.com/step-motors/engine ... ationship/
But there is something of a torque curve at the vendors website. It tells 1/2 of the story.
So, as the OP said, it should work ... if the RPM's are ramped slowly enough and if the driver is really delivering the expected current. Remember that the rotor and spindle have some inertia and take torque to accelerate them.
@ the OP: when you were experimenting w/spindles sizes and accelerations, did you ever find a slow enough ramp so the original spindle worked ? Did you limit the top speed ? Could a slow ramp to a higher max RPM work ?
I note the graph says "half step" but doesn't micro-stepping reduce the motor's torque ? Or have I got it reversed ?
Lastly why not hinge the dog door at it's top and then lock/unlock the bottom, w/appropriate signals to the dog ? Let the dog or gravity do the "heavy lifting" ? No guillotine needed.