Stepper Motor Selection

The step rate is achieved by the rate and number of pulses fed into the stepper controller. Each pulse will result in a preselected step.

A 555 is a candidate to supply a rate.

Note that Stepper motors with a build in/on controller are available.

What do you intend to drive the motion from ?

It is possible to drive up to 4 steppers at different rates from a computer via the printer port.

Is the software to run four steppers from the parallel port readily available?

Will appreciate if a link is provided

Thanks

dulhas

http:\\www.machsupport.com/

Go back to fundamental kinematics. You say that these two payloads will be 8kg and 4kg respectively, well how will they move? If the two masses will just be spun on the end of the motor shafts with the center of mass of these loads in line with the axis of rotation of the motor, then the kinematic calculations will be fairly easy. You will just have to make a moment of inertia calculation or estimate from a known similar geometric shape. Clearly in this case the 8kg load will require a larger minimum size motor than the 4kg load.

If instead the center of mass of these payloads will be offset from the motor's axis of rotation then you will have to consider the difference in the lever arm lengths for the masses involved. If the 4kg center of mass is 5cm away from the axis, while the 8kg center of mass is only 1cm away from the axis then the 4kg mass will require the larger minimum size motor. Don't forget that if these masses now have any elevation changes in their travel you should also include the added effect of raising and lowering these masses.

If instead these two motors will be moving linearly instead of rotationally, you will have to translate the kinematics of linear motion to the circular motion at the motor shaft. This can be just a simple rope wrapped around a diameter shaft (winch configuration) or a threaded rod stage assembly.

Now that you've identified how the masses motion will be translated to the rotational load on the motor, you must identify the velocity and acceleration components you desire for these masses. Translate these motion parameters back to forces and momentum loads that your motor shaft will see. Now you can select a motor with a certainty that you do understand the forces required.

Instead you can just choose a motor and driver at random and hope that everything is big enough to move things fast enough but cheap enough for your budget.

Depending on the mechanical configuration, holding torque may be necessary. The inertia of the load does not disappear, when the drive to the stepper stops. How many more steps will the load move on its own, before stopping? The stepper's positioning information is lost then.

Worm screw gearing is self locking from the load. Loss of drive will not drop (or some such) the load in an uncontrolled fashion.

Using a controller, in the final account, you do not select select the stepper rate. Ramp up, moving speed, ramp down is what is selected. Remember, inertia prevents sudden changes in load's speed.

IF this supposed to be a directly coupled rotary table, the few kg load will set up interesting oscillations, and resonances, with guaranteed cogging. Detailed mechanical calculations are necessary.