# Regarding the formula for rpm

Hello people,

I am working on a project where I need to check the acceleration of the motor in terms of G. In this, I am using Nema 12V stepper motor of 200 steps and DRV8825 driver. I am using this motor in 1/4 mode. Could you please tell me the formula to calculate the RPM, acceleration and velocity in terms of G. Thanks in advance.

Cheers,
Raj

Hello, Raj.

I’m not sure what you mean by “G”, but I do not think your question makes sense. There is no formula for the speed or acceleration of the motor as those are determined by your inputs to the motor driver and specific to your setup.

-Patrick

Hello Patrick,

Thanks for replying. G force is relative centrifugal force which is calculated in radius of motor and rpm. Basically in terms of acceleration 1 G is nothing but 1 G = 9.8 m/s2. I wanted to know where stepping affects the speed of the motor or not. Like in full step and in 1/4th step, will the speed remain same? And second thing, in full step if you mount something on the motor, it creates noise. So could you help me how to reduce that? Thank you.

Hello.

I have moved this discussion to the Motor controllers/drivers and motors category. If given the same sequence of inputs, the motor will rotate at 1/4 the speed in 1/4-stepping mode than it would run in full-stepping mode. I think your best solution for reducing the noise will be to use some level microstepping instead of full stepping.

-Patrick

Hey patrick,

But there’s a problem. While calculating G force, the formula is

RCF = 1.12 x Radius x (rpm/1000)*2

where, the Radius is 0.1065 m

and what is found that, in full stepping it is giving the exact RPM for 1 G that is 92 rotations,
where if i operate my motor in 1/4th microstepping, it is giving 80 Rpm. Could you tell me the reason behind it or anything where i can get the exact rpm for the microstepping as well

Hello.

You directly control your motor’s step rate through your input to the STEP pin. I would focus on measuring the actual RPM of your motor rather than the centrifugal force while you are trying to get it working. If things are not working correctly, then maybe your load or step profile is causing steps to be missed. If the actual speeds are right but the forces are wrong, then there’s probably a mistake in your equations or how you are applying them.

-Patrick

Hello,

But i need to make a program where the speed and acceleration should be calculated in terms of G. Could you suggest me the code fro the speed of the motor if the distance is also involved as i said?

Hello.

Unfortunately, I do not have any suggestions for you.

-Patrick