Speeding up Stepper Motor, need some help pls..

[forever99482]

Hi all,

I have a y129, 6 coils, 2 common stepper motor. I'm using a PIC16F648A and ULN2803 to drive it. I've got everything working except it cant go fast enough when I connect the wheels to it.
1)Any idea of increasing the speed?

2)I realise that the torque of the motor is inversely proportional to the speed, but is it possible to get a large torque at high speed?

The stats of the motor is shown below:
Step angle : 1.8 deg/full step
No. of phase : 4
Rated Voltage : 12V D.C
Rated Current : 0.16A
Winding resistance : 75 ohm
Winding inductance: 60 mH
Holding torque : 900 gf-cm (gram-force centimetre)
Detent torque : 150 gf-cm

I have supplied both the commons with 12V and the right sequence, but just can't get it to run at high speed (gonna put it in a race), could anyone help me please?

 

[Nigel Goodwin]

Well steppers aren't fast at the best of times - so if your competitors are using DC motors you've probably lost already?. But to get them to go faster you need to feed them off a much higher voltage (48V), and limit the current to them - easiest method is to feed the stepper via wirewound resistors, or you can drive them with PWM.

So presuming this is a mobile robot type device?, you need some more batteries or a suitable inverter.

 

[j.p.bill]

Steppers have an upper limit to their response - most often 5000 steps/sec. That translates to 25 RPM. That's a built-in limit.

 

[forever99482]

the whole class is provided with stepper motors, so I pressume everyone is using it anyway.

To limit the current do I just stick a resistor from the driver output to the motor input? As far as I know, to increase the speed of the stepper motor is to increase the stepping rate, but I don't really know how to increase the stepping rate....

 

[Nigel Goodwin]

the whole class is provided with stepper motors, so I pressume everyone is using it anyway.

To limit the current do I just stick a resistor from the driver output to the motor input? As far as I know, to increase the speed of the stepper motor is to increase the stepping rate, but I don't really know how to increase the stepping rate....

You would normally use just two resistors, in the 48V feeds to the centre taps of the two coils - increasing the stepping rate is generally a simple software change.

Try googling for "stepper motor tutorial", there is LOT'S of information out there!.

 

[Gaston]

i am running a stepper with a stepper controler and a pic so its a similar situation. for me to increase the speed i have to change the code in the pic to send out a higher frequency pulse to the controller.now how that is done depends on how the code is written

 

[j.p.bill]

Here is about all the info on steppers there is - **broken link removed**

 

[Sceadwian]

Increase the voltage, as long as you don't violate the insulation rateing of the motor windings current is significantly more important than voltage. Steppers, and motors in general use more current when stalled, they'll use less when in motion, the nameplate rateings you listed are stall rateings, which slow moving steppers run at, higher speed steppers can be run at any voltage that dosen't over current the motor or violate the insulation rating. 12 volts is NOT the insulation rateing of the motor. This is easiest to achieve using a constant current source for the stepper windings rather than a voltage source. Torque at higher speeds will be increased dramatically. It's hard to recommend a maximum supply voltage because I'm not very good with motors. One important variable that will help you chose the proper maximum voltage is the maximum power dissipation of the motor, if you're not sure and chose a voltage too high the motor will burn out, it's probably best to put some kind of temperature sensing element on the motor until you're sure you can maintain it at a safe temperature.