Is the stepper too small

stepper motor

I'm building a machine that uses a single stepper motor connected to a gearbox. I'm running it at full steps and I seem to only be able to reach 1000 steps per second with a 200 step/rev motor. Much higher and it stalls and makes a lot of bad noise. I really would like to be going at least 2000 steps.

Here's some specifics on the hardware:

The original machine used a pulley between the motor and gearbox. Because I don't want slippage, I've switched to a gear and chain setup, but I think the gear ratio is reasonably similar. I had hoped that this stepper was powerful enough to replace the original DC motor, but it doesn't seem to be able to run quite as fast. Did I pick the wrong stepper?

On a related note, is there any way to do a comparison between a stepper and a regular old DC motor? Or is that comparing apples to oranges?

Best Answer

You don't say it, but your problem may be that you're trying to start the stepper at full speed. If so, there is a maximum speed (which varies somewhat with load) beyond which a stepper will not accelerate, and this speed is normally well below what you can reach with a gradual increase in speed. Google on "stepper motor torque curve".

The problem is that, with a 4-phase stepper such as you are using, if the shaft angle lags more than 2 step angles behind the commanded angle, the torque reverses and the motor sits and vibrates and makes horrible noises. This is not, technically speaking, a stall condition, where the shaft does not move at all.

The torque-speed curve for your motor can be found at http://www.kelinginc.net/KL34H2120-42-8AT.pdf and indicates that the motor can be run at 5000 steps/second, which suggests that your problem is your attempt at fast start.

If, on the other hand, you've already tried a slowly increasing step rate while running, then you probably do need a heftier motor. However, my calculations for a .144 hp motor at 10 rps gives about 2 Nm torque, and the linked torque curve for your stepper is about the same, so I wouldn't expect a problem. Unless, of course, you've modified your mechanical setup somehow.