How to increase the torque of a stepper motor?

[toos]

I have a stepper motor with the following specs:
- 5V
- 7.5DEG/step
- 6.5 Ohm

I drive it using a ULN2803A with pulse from a 68HC11 Microcontroller. However, the motor seemed doesnt have enough torque for my application (a little bit more will be pretty good).

So may i know, what are other ways that i can try other than changing the motor? (I've tried increasing the delay, which result in lower speed, but it doenst help).

 

[Nigel Goodwin]

It's common practice to feed steppers from a far higher voltage than their rating, with current limiting resistors (wirewound ones) in series with the supply. This allows them to run at higher speeds, and may be helpful to
you?.

Try **broken link removed**.

 

[panic mode]

you can also try to add some gears to trade some speed for torque...

 

[evandude]

You can overdrive stepper motors most of the time. I have a friend who runs 5v motors at something like 15v with no current limiting. obviously, that's a bit extreme, and his motors tend to run somewhat hot, but you can at least up the voltage a little above the rated voltage.

oh, and nigel... by the way, generally with steppers you do NOT want to use wirewound resistors.

the whole point of using a higher voltage with a series resistance is that it increases the REAL component of the total impedance, so the load looks more like a resistor and less like an inductor. the reason for using higher voltage is to get current flowing through the inductive coil of the motor more quickly... by using a wirewound resistor you are adding to the resistance AND the inductance, so you won't get much of an improvement (of course, the resistor will have lower inductance than the motor coil so it will have some improvement, but still, it does defeat the point to some degree)

 

[Nigel Goodwin]

oh, and nigel... by the way, generally with steppers you do NOT want to use wirewound resistors.

the whole point of using a higher voltage with a series resistance is that it increases the REAL component of the total impedance, so the load looks more like a resistor and less like an inductor. the reason for using higher voltage is to get current flowing through the inductive coil of the motor more quickly... by using a wirewound resistor you are adding to the resistance AND the inductance, so you won't get much of an improvement (of course, the resistor will have lower inductance than the motor coil so it will have some improvement, but still, it does defeat the point to some degree)

But they all do use wirewound resistors!, you can't get non-wirewound in sufficiently high ratings.

 

[evandude]

They are hard to find, but they do make them... for instance here is an 8 ohm 20 watt non-inductive resistor, as you can see right on it:
**broken link removed**

 

[Nigel Goodwin]

They are hard to find, but they do make them... for instance here is an 8 ohm 20 watt non-inductive resistor, as you can see right on it:
**broken link removed**

Yes, but it's still wirewound :lol:

I'd also like to test one and see how non-inductive it is, bearing it mind it's probably designed for audio use (being 8 ohm).

 

[toos]

Thanks for the suggestions...

I've tried to increase the supply to 9VDC, however, after some time, the stepper motor becomes too hot to be touched. I wonder if that can damage the motor.

May I know whether connecting a wirewound resistor in series to the motor supply can reduce the power dissapation (since the current is reduced)? However, since the current is reduced, will the torque be reduced too?

 

[Nigel Goodwin]

Thanks for the suggestions...

I've tried to increase the supply to 9VDC, however, after some time, the stepper motor becomes too hot to be touched. I wonder if that can damage the motor.

May I know whether connecting a wirewound resistor in series to the motor supply can reduce the power dissapation (since the current is reduced)? However, since the current is reduced, will the torque be reduced too?

Did you try reading the tutorial I gave the link to above?, it shows how to calculate the resistor values - try it and see!. It's intended to allow the stepper to move faster, but try it and see what happens.

BTW, what are you trying to do with the stepper?.

 

[toos]

Yup. I've actually gone through the site before you gave it to me. And, I'm using the Hi-torque, 2-phase stepping sequence as suggested in the site.

I'm building a pan-and-tilt unit that holds a web camera. I actually need more torque than speed as the stepper is not able to lift the camera up to a certain degree that i require it to be.

 

[Nigel Goodwin]

Yup. I've actually gone through the site before you gave it to me. And, I'm using the Hi-torque, 2-phase stepping sequence as suggested in the site.

I'm building a pan-and-tilt unit that holds a web camera. I actually need more torque than speed as the stepper is not able to lift the camera up to a certain degree that i require it to be.

I would suggest using RC servos instead, much more power, smaller, lighter, and they provide absolute postitioning - which steppers don't!. They are also even easier to drive, just a variable width pulse (not that steppers are hard!).