Any torque capability in excess of what the application requires comes at the high cost of
unnecessary motor heating. Excess torque capability beyond a reasonable safety margin will never be
used but will exact the penalty of an oversized power supply, drive stress and motor temperature.
The place to start is to determine the load torque in oz/in, including the torque necessary to
accelerate the load. The next step is to come up with the maximum speed the application has to operate
at in full steps per second using the formula below. RPI is the revolutions per inch after the motor turns
through the transmission, RPS is revolutions per second and PPS is the number of pulses per second
from your step pulse source.
(Desired IPM * RPI) / 60 = RPS
RPS * 200 = PPS
Multiply the PPS value by the number of oz/in determined previously and divide the total by
4506. The answer will be how many watts mechanical are required from the motor to meet the load
from the application. When picking a motor, choose one with 40% more than the calculated power.
Below is an example of the equation completed for a load requiring 450 oz/in with a 3 TPI leadscrew and
a desired IPM of 300.
(300 * 3) / 60 = 15
15 * 200 = 3000
(3000 * 450) / 4506 = 299 oz/in
299 * 1.4 = 419 oz/in
As you can see, you will want to use a motor with a rating of 419 oz/in for this application.
You need to know how much torque is required to lift the or lower the bed mechanism or gantry and how fast you want/ need to move it.
also nema 23s tend to need like 3 amps of power way more than pololu shield will provide .
also keep in mind that the nema size has little to do with torque of a motor you need to make sure you motor has enough torque but does not overdraw amps and blow a driver.
Also having 4 lead screws vs two should not make that much difference in motor requirements.
You may need to build you design measure required torque then select the motors .
I can not tell you what motor you need with no data to work with.
Based on experience and observations of machines a nema 17 should be plenty for what you propose but again you need to take some measurements and do some math.
If this is your first 3d printer I suggest just buying one or at least a kit rather that doing a scratch design and build.
tin
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