stepper motor torque Question?

[cwickham]

Hey

i was wondering if anyone knows how to increase the torque of a stepper motor?

is there easy ways to do it and then better ways to do it

thanks for the help
craig

 

[Nigel Goodwin]

Feed them from a much higher voltage, with current limiting resistors - more speed, more power, more torque. Feeding a 12V stepper from 48V is pretty common.

 

[woz]

Torque

Nigel, do you even know what a Stepper Motor is? More voltage won't increase speed... Your controller circuit controls the speed... Driving a motor with 48 V instead of 12 V and with a current limiting resistor is exactly the same as running at 12 with the resistor provided that the current passing through the motor is the same, that sounded kinda obvious... anyway

to Increase the torque there are a few things you can do that I know of:

-Drive the motor with it's nominal voltage (12V in this case)

-Use Speed reduction gears, like the ones used in Servos. If you reduce the speed by 50% you will increase the torque by 50%, reduced by 500% means 500% more torque, etc. Just like pulleys

-I have read that driving the motors at a slow rate increases the torque, but I'm not sure about this.


I think the best way is to add reducing gears.

WoZ

 

[HarveyH42]

It's like over-driving an LED to make it brighter for a brief pulse. I would think increasing the voltage would only be good for some applications.

Anyway, there are at least 2 good CNC forumn sites, CNCZONE is the best. You'll find many good ideas there, from people who abuse the hell out of steppers.

 

[Diver300]

Stepper motor windings have significant inductance, so the current takes time to rise and fall. This reduces the torque as the motor turns faster.

Applying a bigger voltage reduces the rise and fall time of the current , so the motor torque falls more slowly as the motor speeds up.

If the voltage applied is bigger than the motor rating, the motor current has to be limited . Resistors can be used. They don't have inducance, so they don't slow the rise and fall much, they just limit the maximum current. This is a very simple improvement that can be made. The downside is that the circuit is very inefficient, with most of the power going to heat the resistors.

A better but more complicated solution uses a current control circuit. In that, a large voltage is applied to the winding. When the current gets to the rated vaue, the supply is removed and the current continues to flow in a freewheel diode. The current is controlled by PWM.

When the current is to be stopped, for the next step of the motor, the freewheel diode is disconnected, forcing the coil current through other diodes, back into the supply. That reduces the current as fast as it increased.
This is much more complicated than some big resistors, but performs better, and uses much less power.

 

[Nigel Goodwin]

Nigel, do you even know what a Stepper Motor is? More voltage won't increase speed... Your controller circuit controls the speed... Driving a motor with 48 V instead of 12 V and with a current limiting resistor is exactly the same as running at 12 with the resistor provided that the current passing through the motor is the same, that sounded kinda obvious... anyway

I know what they are, but apparently you don't have the faintest idea?

This isn't something I've made up, it's the standard method of feeding stepper motors - try googling for "stepper motor tutorial" - you will find it enlightning and educational.

For a first post you haven't really made a very good impression?.

 

[woz]

...

thought you meant the angular velocity, sorry

 

[Boncuk]

Stepper motor torque

Google "wave drive". That kind brings about more torque.