mesamune80

Do you mean for 24V stepper i use 24Vdc to test out the coil polarities?could this burn the coil?

my stepper motor is here:
http://www.imseuropehome.com/Product...MH2_2222_D.pdf

hjames

The main limit that you need to observe when dealing with steppers is the max current limit -but I think they calculate the voltage based the coil resistance, so it should be okay. For testing purposes it's probably easier to use some fraction of the rated current/voltage though - you just need to see which way a coil pulls the rotor.

hjames

Erm, so if you hook up the stepper according to the "Series connection" diagram on the lower left, that's all you need to do... And that's a 2Vdc stepper motor you have there...

mesamune80

2Vdc?not 24Vdc?ya i am facing a problem here,when i hook up the power soure for the dc motor with 12vdc(same common with main board) the motor move but with 24vcd(diffferent common with main board) the motor wont move,do need to equalize the common for the driver and for the stepper motor?for ur knowledge i am using 12vdc as my main board power source,it then goes through a regulator so i got my 5v for my microcontroller and 5v for my stepper driver.what is the reason behind this?i am still scratching my head on this >_<"

hjames

If you are using this particular motor with that driver chip using an L/R drive, then you must choose R so that the maximum current is 3Amps. This stepper motor is meant to be driven with a "chopper" or current limited stepper driver. If you put 12 or 24Volts across a coil in this motor it *WILL* be damaged, What happens is that the rotor gets demagnetized if the current exceeds the rating by a significant amount.

As for your circuit, I can't understand what you are describing - if you are asking about ground connections - everything should be grounded to the same point.

mesamune80

Ic, nowonder my driver suddently become hot when i connect 12vdc to the motor,but the current is just 500mA
how come the driver can become hot?or i really need a special circuit to drive this kind of motor?Thanks.

hjames

Well, the motor(if hooked up correctly) will have have a limit of 3Amps/phase. R = V / I = 12 / 3 = 4Ohms. Since the stepper itself is .76Ohms, the resistor needs to be atleast 4 - .76 to avoid toasting the motor....

However the chip you've chosen can only drive 1.25A, so chances are that your motor is "safe" only because the driver chip is getting exceedingly hot.

You'll need to post your schematic (along with how you've connected the motor) for any useful response...

Incidentally, the chip I'm using for my stepper motors is the A3977 (by Allegro, the same manufacturer). This chip has current chopping so it regulates the current properly. There's a number of other chips that would also work, the A3977 was just easier to use.

James

phalanx

I can attest to the quality of Allegro parts. I've used their A3984 in several commercial and personal products. Fantastic little chip that frees up quite a bit of processor time, especially when controlling 3 axes with microstepping.

mesamune80

ic,that's why my driver burn out =.=" one more thing,how to increase the torque of one motor?or the maximum torque is already fixed by each motor?

hjames

Torque depends on magnetic flux, which is limited by the magnets in the motor. Exceed the maximum currents => exceed the flux => toast the magnets, and you'll have a dead motor. I think steppers, in particular, depend heavily on the magnets, so yeah, whatever torque is listed on the data sheet is the maximum "safe" torque you can get out of the stepper.

James

mesamune80

which mean to say that,it is independent on the driver is it?no matter how good your driver is, it still cannot exceed the torque limit of the motor?

phalanx

There is no hard "torque limit" in an electric motor. You can likely exceed the rated current of the motor and produce torque higher than what is listed in the datasheet. You will begin to get diminshing returns due to field saturation in the magnets. Keep increasing the current and you could eventually damage the magnets.

Torque is related to the current flowing through the windings of the motor. More current = more field. More field = more torque.

hjames

Physical limits are hard to bypass... I point out steppers in particular because they are pretty darned reliant on magnetics. As far as I know, if you disassemble any stepper motor and pull the rotor (with magnets) out of the housing, that'll damage the magnets. If you want more info, search for "stepper demagnetization".

This person has a useful picture of torque vs speed vs current for some stepper - notice that torque drops off pretty quickly versus speed - regardless of the current. I think this is pretty typical for steppers.

http://www.krupin.net/serendipity/in...wn-design.html

mesamune80

now i think of want to drive the bipolar motor and i think i can no longer use this UCN5804B to drive them,as mention by phalanx and james the A3984 and A3977 both are DMOS microstepping Driver with translator,But can i know how to hook this to my microcontroller so that i can easily drive them?Thanks.

phalanx

Just read the data sheets. All the motor controllers made by Allegro Microsystems are pretty easy to interface with.