[adroitguy]

Hello ,
I need some advice from the pros.
I have a bi-polar stepper which is rated for 12V / 0.67A/phase.
This motor is supposed to deliver 7Kgf.cm (97.21 oz.in).
I am driving this with a L297/L298 combination .
I attached a weight to the pulley and tried lifting a dead weight and found a maximum pulling torque of 4kg.cm @ 60rpm. I am inable to go beyond that with this.
I am using a 24VAC transformer with a bridge and a 2200uF cap to filter the AC.

Is this a valid design ?Where am I going wrong ? I need 7kg.cm atleast upto 120RPM .
Can anyone help me ?
I will supply any additional info as required .

Regards

[ger21]

That 7kg would be with a 1cm dia. pulley at 0 rpm. Once it starts spinning, the torque will start to drop. Sounds like you need a bigger motor, preferably with a lower V rating.

[CJL5585]

I second Ger21's recommendation.

Jerry

[ViperTX]

Yes, you have to look at the torque curves for steppers and determine the RPM range where you want to run.

[eidos]

Hello ,
I need some advice from the pros.
I have a bi-polar stepper which is rated for 12V / 0.67A/phase.
This motor is supposed to deliver 7Kgf.cm (97.21 oz.in).
I am driving this with a L297/L298 combination .
I attached a weight to the pulley and tried lifting a dead weight and found a maximum pulling torque of 4kg.cm @ 60rpm. I am inable to go beyond that with this.
I am using a 24VAC transformer with a bridge and a 2200uF cap to filter the AC.

Is this a valid design ?Where am I going wrong ? I need 7kg.cm atleast upto 120RPM .
Can anyone help me ?
I will supply any additional info as required .

Regards

12 volts dc?
hummm
no good for 297 298 drivers!
these motors are high resistance phase ! + - 10 ohm ?!
I recommend you to measure the resistance of 1 phase, and itself is taller than 3 ohms, that motor are not all right for the pilotage in pwm 297 298 .
you will also have always a low couple feeding them to 40 volts.
visit my site!!
hi

[adroitguy]

Thanks Ger and all of you for your kind reply.

I have measured the torque at a pulley of 50 mm dia. ,where it is lifting about 1.5 kg , hence (1.5 * 2.5 = @ 4 Kg. cm ) .

Sadly I have already purchased the stepper and it cannot be exchanged for a lower voltage motor. My only recourse now seems to be to hack a solution.

Would increasing the voltage to 36V give me a better torque even at lower speeds ? As per my understanding the only way to get a better torque at a higher speed is to increase the voltage . Would this help for lower speeds too ?

[ger21]

As per my understanding the only way to get a better torque at a higher speed is to increase the voltage . Would this help for lower speeds too ?

It might help. but I think the bigger problem is that the motor is barely adequate torque-wise.

[adroitguy]

It might help. but I think the bigger problem is that the motor is barely adequate torque-wise.

Hi Gerry ,

What I am trying to get across is that, I am trying to see if the motor is meeting its specs , which it is not . It does not deliver the rated 7kg.cm which it is supposed to deliver.

Eidos , unfortunately your page is in Italian , difficult for me to comprehend !!!

Thanks for your replies and that of others.

Regards
Thomas

[adroitguy]

12 volts dc?
hummm
no good for 297 298 drivers!
these motors are high resistance phase ! + - 10 ohm ?!
I recommend you to measure the resistance of 1 phase, and itself is taller than 3 ohms, that motor are not all right for the pilotage in pwm 297 298 .
you will also have always a low couple feeding them to 40 volts.
visit my site!!
hi

Hi Eidos ,
By couple I think you mean torque , so you say that with L297/L298 I will not get the torque ?
My motor's resistance is 17.5 ohms. Do you have any schematic posted on your site , can you give me a link ?

Thomas

[ger21]

Hi Gerry ,

What I am trying to get across is that, I am trying to see if the motor is meeting its specs , which it is not . It does not deliver the rated 7kg.cm which it is supposed to deliver.

Regards
Thomas

Like I said, the rated torqe is at 0rpm, without the motor spinning. You'll get less torque with it spinning. Will it hold 7kg without spinning?

[adroitguy]

Like I said, the rated torqe is at 0rpm, without the motor spinning. You'll get less torque with it spinning. Will it hold 7kg without spinning?

Hello Gerry

Yes the motor holds 7 kg without spinning , but that does not help me much .
It is made by a company called srijan drives , but I am not able to get this data from them .
have to show it to a customer , where do you think I can get the torque / speed characteristics for this motor ?
Would this curve be more or less same for most bipolar motors ?

Regards
Thomas

[ger21]

Would this curve be more or less same for most bipolar motors ?

Regards
Thomas

With similar specs (volts and amps), torque curves should be similar.

[ger21]

Hello Gerry

Yes the motor holds 7 kg without spinning , but that does not help me much .
Regards
Thomas

Then the motor IS meeting it's specs. You just need a bigger motor.

[eidos]

Hi Eidos ,
By couple I think you mean torque , so you say that with L297/L298 I will not get the torque ?
My motor's resistance is 17.5 ohms. Do you have any schematic posted on your site , can you give me a link ?

Thomas

hi tomas
him, as she says, with motor from 17,5 ohms phase, is impossible to pilot them with the couple 297 298.
because for the law of Ohm that motors require at least 170 volts to be able to correctly be piloted in bipolar pwm, end obtain full couple.
those are motor only unipolar !
or drivered with old transistors driver, " monopolar"
in bipolar pwms are not all right.
excuse me, but they are not available schemes of my cards, that are commercialized you already climb on and ready for the use.
hi