# Using a stepper motor to generate an impulse.

Hey all,

I was thinking of a project in which the stepper motor would have an arm on the shaft. So, can the shaft be controlled precisely so that the other end of the arm hits a structure and comes back such that it produces an impulse on the structure (The goal is to provide an impulsive force to a structure)?

Any help would be appreciated.

Thanks

Yes.

Calculate the torque needed. Then search for steppers providing that torque.

It's not that easy. How fast can the stepper move forward, stop, and move backward again? How fast will the arm knock? The impact (impuls) depends on the mass, velocity and flexibility of both the arm and the object.

Accelerating the mass in the arm calls for torque. But, yes, the Pull In Rate of the stepper is important if fast acceleration is needed.

DrDiettrich:
It's not that easy. How fast can the stepper move forward, stop, and move backward again? How fast will the arm knock? The impact (impuls) depends on the mass, velocity and flexibility of both the arm and the object.

How fast it would go depends upon the amount of impulsive force I want to exert on the structure which would vary.
The stopping and the backward motion should be fast enough that it doesn't give the structure a second impulse.

The mass of the arm would be around 25 gms and it would be stiff. The stiffness of the structure would vary though.

Thanks

I suspect a stepper motor used directly would not be suitable unless a single step is sufficient. And you don't have any control over how fast the motor moves with a single step - that just depends on the magnetism and the mass of the motor and whatever is connected to it.

If you are trying to use the rotational velocity (and the rotating mass) of the stepper then a stepper motor is no different from any other motor. And if the stepper motor is rotating quickly it almost certainly won't stop instantly.

My inclination would be to use a motor to "charge" a mechanical device that will deliver the impact - for example to pull back a piston against a spring and then have a separate mechanism to release the piston using the force of the spring to deliver the impact.

...R