sorry still new to this... i hoping your can break up some the math bit more
understand.... what u say ..but need to know how you get some of your rpm cal and ipm.
thanks
Originally Posted by jcc3inc  Eloid,
To get the true picture of your setup, you need to look at the speed vs torque curves for a given stepper. Sometimes a smaller motor has better performance than a larger one when operating at higher speeds. I used a smaller one below.
I chose to use (2) of the 960 oz-in steppers from your source. I arbitrarily chose a gear reduction ratio of 3:1 operating the motor at 5000 half steps/sec. This gives 750 RPM at the stepper shaft, 250 RPM on the output resulting in a traverse speed of 785 IPM. The choice is kind of arbitrary; you might try different scenarios.
The stepper torque has declined to 354 ounce inches at this speed. With (2) steppers on your heavier axis, you have 758 max ounce inches of torque,
354x2=708???????
and 3x this at the drive shafts
or 2124 ounce inches. At a 1/2 inch radius pinion this results in about 4248 ounces or 265# max of force.
if was 1"? PINION????
Your large carriage weighs 150#; this is 150/32.2 = 4.66 slugs (mass).
32.2? where did this come from?
a = f/m so your acceleration will be 265/4.66 = or 57 ft/sec squared.
The time to accelerate to full speed will be t = Vfinal/a, 785 IPM = 65.4 ft/min.
Now t = 65.4/57 = 1.1 seconds to accelerate 150# to 785 IPM. (That's flyin' right along, you know!)
At 758 IPM the out shaft goes 758/3.14159 = 250 RPM, motor at 750 RPM, 750/60 RPS.
Assuming you will use 10x microstepping, the max step pulse rate will be (750/60) x 2000
which is 25000 pulses per second.
The resolution will be running a pinion of 3.14159" circumference from 6000 pulses per pinion revolution, giving .0005236"/pulse, about a half thousandth per pulse.
In my calculations above I neglected the inertia of the steppers (and friction and load force
which are unknown to me).
I hope this helps your choosing.
Regards,
Jack C. |