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I am using a PM2515-03 Stepper motor and with the following ratings: Current/phase= 0.5A rated voltage= 5V step angle=7.5 degrees inductance = 2.7 mH resistance/phase = 10 ohms Now, in order to start the motor I need to figure out the minimum delay between pulses that will tend to rotate the motor. If anyone knows how to calculate the delay please explain in full details, how can I calculate the delay. Thanks in advance.

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  • \$\begingroup\$ Minimum starting speed will depend on the load and inertial load and how much voltage the driver can deliver to overcome the inductance. Usually you have to ramp the speed up and down. You can just try it. \$\endgroup\$ – Spehro Pefhany Nov 6 '16 at 1:07
  • \$\begingroup\$ I dont have to drive any load this time I just wanna rotate it freely @SpehroPefhany \$\endgroup\$ – Busani B-Kingz Nkosi Nov 8 '16 at 23:21
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You do not state the rotation rate you want, so I'll give you the time required for a single step from rest. Obviously, once you get the load spinning, the step time goes down. However, as speed goes up the available torque goes down, so at some point the load losses balance the torque available, and no further acceleration is possible. Additionally, at some point the inductance of the motor will prevent the winding currents from changing, but that is a more advanced subject.

1 - From the motor data sheet, determine the motor torque T at your desired current.

2 - From analysis of your load, determine the load angular moment of inertia.

3 - From the motor data sheet, determine the intrinsic motor moment of inertia, and add this to the load MOI, and call it J.

4 - Using the results of 1 and 3, determine the time required to accelerate from rest to one step angle theta, where $$ \Theta = \frac{T\times t^2}{2J} $$ or $$t = \sqrt{\frac{2J\Theta}{T}}$$

You need to be careful of your units, especially Theta, which must be in radians, rather than degrees. Also, this assumes no frictional losses in load bearings or something similar.

This is a very conservative number, and depending on the motor you may be able to get away with about 70% of this step time.

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