[DimiOrla]

Hello everybody,
I planning to build a small cnc for PCB machining, and use parts that I already I have.
But I need some help with my motor controller.

My motors have 6 wire and I was planning to use them as bipolar and drive them with the 3977 or the L297-8 combination. My next choice would be tachus42's 3 Channel Discrete unipolar board
From what I have read on the wed bipolar motors have more torque than unipolar. But the graphic of the manufacturer confused me (see attachments.)

My next question is, would a 20v/4.5A/90W power supply be strong enough to drive three of them?

Thanks in advance for your help.
Dimitris.

[DennisCNC]

Those motors a 48 steps per rev, that will not give you good resolution, unless you have very low lead screws. And they are very small and might not have enough turque to even turn a screw. Get your self three of these:
http://cgi.ebay.com/3-CNC-Stepper-Mo...QQcmdZViewItem
and they will make your machine move very smooth.

[DimiOrla]

Thanks for you answer Dennis.

I am planning to use then with a 1:5 gear ratio and a 8mm screw with 1.25mm pits.
So it is more like (48*5)/1,25=0,005mm. The machine its self will be rather small, something like 60x60x20 cm.

If I am reading the graphic correctly the motors will give in unipolar 2 Nm and bipolar 1,5 Nm that is 212 and 242 oz. Is that correct?

P.S. This machine will de just for learning purposes.

[fyffe555]

Thanks for you answer Dennis.
If I am reading the graphic correctly the motors will give in unipolar 2 Nm and bipolar 1,5 Nm that is 212 and 242 oz. Is that correct?

The graphic says the max torque is 2000 and the scale is N.M. x10 -4 so thats 0.2NM or ~28ozin.

These are very small motors.

[DimiOrla]

Thanks fyffe555,

So the unipolars are better at 0,2 instead of the bipolar at 0,15. That is weird it goes against all I have read.
If I gear them down (0.2*5=1Nm), I think with minimal friction they will be good enough for one kilo of load.

P.S. Under 24v I don’t need any limiting resistors write, how about the amper’s (4.5) are they ok for three motors?

[LZ1TWB]

Hello DimiOrla,
I could tell you some tips about this motor.
First of all it is unipolar, which means it has twice as much wire in itself with twice lower cross section. Unipolar motors are easy to control as you need only 4 transistors to turn each of the 4 coils to ground / two by two coils are connected with a centre to + voltage/ Driving a unipolar motor in bipolar mode is not good as only one of the windings is used - you cannot put much current in it and the torque is then less. It is said that a bipolar motor compared with the same size unipolar has more torque because you have only two coils with thicker wire that can conduct more current before getting too hot.
DennisCNC said that it is low resolution motor 7.5 degrees step - try using some like 1.8 as they are more common, which driving it in half step gives a 0.9 step. If you intend to use a gear you have to spin it quite fast in order to have some good speed of travel. 24V is high for a cnc motor and if you drive it with a 24V supply you will certainly get nothing from it as current cannot get high enough to maintain the desired torque /coil induction issues/. It will be limited to certain rpm. Stepper motors are mostly used with a voltage many times bigger than the specified, but of course some sort of current limiter should be placed. Most steppers have a low voltage specified 2-3Volts but are normally used at 24 for example. Higher voltage means more torque at high speeds.
There are so many things that could be said about steppers, just ask if you need something, I see you are going to learn in cnc stuff, keep going, it will become very interesting to you.
I remember my first cut on my mill, I've drawn half a ball and machined it in foam and was pretty happy then.

Greetings,
Todor

P.P. - someone correct me if I've made a mistake somewhere.

[DimiOrla]

Thanks LZ1TWB this makes more sense now.

[brijkalani]

Hi,
The explaination you gave is really good and helpful. I have a querry to which you might be able to help. I am not building a cnc but using steppers for other automation purpose. i have got NEMA 23stepper motor (1.8 degree, 2.0 A) which has 5V written on the datasheet. Now the driver i have got is to be run at min 20V. I did connect to a 20v, 5.0A power supply and interfaced with my pc (c progam) but the rpm was too slow.

Can you guide me what should i do to increase the speed of the motor. i thought it was the clock speed of the computer. But i guess it should be enough to turn the motor at greater speeds.

or is it some thing else i need to change?

As the motor ran with 20V 5A supply on the driver I guess power supply should not create a problem. if you think i am doing in wrong manner please let me know.

Thanks in advance.

Hello DimiOrla,
I could tell you some tips about this motor.
First of all it is unipolar, which means it has twice as much wire in itself with twice lower cross section. Unipolar motors are easy to control as you need only 4 transistors to turn each of the 4 coils to ground / two by two coils are connected with a centre to + voltage/ Driving a unipolar motor in bipolar mode is not good as only one of the windings is used - you cannot put much current in it and the torque is then less. It is said that a bipolar motor compared with the same size unipolar has more torque because you have only two coils with thicker wire that can conduct more current before getting too hot.
DennisCNC said that it is low resolution motor 7.5 degrees step - try using some like 1.8 as they are more common, which driving it in half step gives a 0.9 step. If you intend to use a gear you have to spin it quite fast in order to have some good speed of travel. 24V is high for a cnc motor and if you drive it with a 24V supply you will certainly get nothing from it as current cannot get high enough to maintain the desired torque /coil induction issues/. It will be limited to certain rpm. Stepper motors are mostly used with a voltage many times bigger than the specified, but of course some sort of current limiter should be placed. Most steppers have a low voltage specified 2-3Volts but are normally used at 24 for example. Higher voltage means more torque at high speeds.
There are so many things that could be said about steppers, just ask if you need something, I see you are going to learn in cnc stuff, keep going, it will become very interesting to you.
I remember my first cut on my mill, I've drawn half a ball and machined it in foam and was pretty happy then.

Greetings,
Todor

P.P. - someone correct me if I've made a mistake somewhere.

[kreutz]

Hi,
The explaination you gave is really good and helpful. I have a querry to which you might be able to help. I am not building a cnc but using steppers for other automation purpose. i have got NEMA 23stepper motor (1.8 degree, 2.0 A) which has 5V written on the datasheet. Now the driver i have got is to be run at min 20V. I did connect to a 20v, 5.0A power supply and interfaced with my pc (c progam) but the rpm was too slow.

Can you guide me what should i do to increase the speed of the motor. i thought it was the clock speed of the computer. But i guess it should be enough to turn the motor at greater speeds.

or is it some thing else i need to change?

As the motor ran with 20V 5A supply on the driver I guess power supply should not create a problem. if you think i am doing in wrong manner please let me know.

Thanks in advance.

What kind of driver are you using, chopper or Resistor current limit? If you are driving your motor without any current limit you are going ruin them, and probably your power supply too.

[brijkalani]

What kind of driver are you using, chopper or Resistor current limit? If you are driving your motor without any current limit you are going ruin them, and probably your power supply too.

Thanks for your response.

I am using a microstepping chopper driver MSD542
http://www.motioncontrolproducts.co....0datasheet.pdf

The stepper motor is
http://motioncontrolproducts.co.uk/p...products_id/90


The driver is connected to the pc via a velleman k8055 USB interface board. It runs quite slow when connecting to one of the digital outputs and running with a simple looping c program.

I also tried to connect with the PWM output from the card. Again its running at very high speed and not able to control the speed with the help of program.

Thanks.

[kreutz]

Thanks for your response.

I am using a microstepping chopper driver MSD542
http://www.motioncontrolproducts.co....0datasheet.pdf

The stepper motor is
http://motioncontrolproducts.co.uk/p...products_id/90


The driver is connected to the pc via a velleman k8055 USB interface board. It runs quite slow when connecting to one of the digital outputs and running with a simple looping c program.

I also tried to connect with the PWM output from the card. Again its running at very high speed and not able to control the speed with the help of program.

Thanks.

I have the same motor, it is the motor I use for testing our "Mardus-Kreutz" controller. The inductance on this motor is so high that it will lose torque at less than 200 r.p.m. (at 1/10 microstep), due to the L/R effect, with a 24 volt power supply (that is the reason why I chose that motor for testing) You will need to get a higher voltage power supply (more than 35 volts) or a controller with midband resonance compensation for higher speeds.

What is the maximum step rate you get from the USB interface board?. What is the step pulse width? What acceleration rate?

[OCNC]

Thanks fyffe555,

So the unipolars are better at 0,2 instead of the bipolar at 0,15. That is weird it goes against all I have read.
If I gear them down (0.2*5=1Nm), I think with minimal friction they will be good enough for one kilo of load.

P.S. Under 24v I don’t need any limiting resistors write, how about the amper’s (4.5) are they ok for three motors?

At 24V, 13 ohms each stepper is drawing .8A so for three steppers you'll need at least 2.4A. If you connect an ammeter to measure current in the steppers vs. speed you'll quickly see that your optimum range will be in the 100 to 200 pps range which for a 48 step motor is between 3 and 4 revs per sec. The trick to getting the most performance out of small motors is keeping the amps as high as possible while using the mechanicals to get the best speed. There is a definite balanced or 'tuned point' to this that can best be arrived at by the process of constructing a simple prototype. If you over drive the motors by increasing the voltage above the rated value you need to add current limiting to protect the motor coils and this in turn necessitates improving proportionately the heat dissipation for the drive circuitry (the extra voltage is converted to heat in the power transistors). This process is ultimately limited but does provide enough gain to be appropriate to a point. As a design process I would first find out what rev per sec you can achieve at .8A current and then get a feel for how much below .8A you can go before the torque falls off. Then knowing the intended rps you can chose a screw thread or gearing that will give you some speed or torque multiplication as the case may be. Then it's just a matter of keeping all of your friction and inertial loads as small as possible. I've also found that it's important to have a clean pulse source. I've been using Linistepper drivers with 1A rated motors (driving them at 1A) with the voltage set at 3 times the rated voltage (3 x 6V for 18V). I'm using Torque Spline lead screws that give me 1 inch of travel per rev. My software has been 'Master 5' demo version. In 'half step mode' at a travel rate of about 90 ipm this seems to give about 30 lbs. of linear force on the drive nut. Note that I'm working at 1.5 rev per sec. I can do no load rapids at about 2.25 rev per sec.

Chris

[brijkalani]

I have the same motor, it is the motor I use for testing our "Mardus-Kreutz" controller. The inductance on this motor is so high that it will lose torque at less than 200 r.p.m. (at 1/10 microstep), due to the L/R effect, with a 24 volt power supply (that is the reason why I chose that motor for testing) You will need to get a higher voltage power supply (more than 35 volts) or a controller with midband resonance compensation for higher speeds.

What is the maximum step rate you get from the USB interface board?. What is the step pulse width? What acceleration rate?

This is the answer i got from velleman (usb interface card) forum.

"The PWM output frequency is fixed and you can't control the stepper motor speed by changing the pulse width.

The state of the digital outputs can be changed every 20ms. So the maximum step rate is 25Hz. If your C code is properly controlling the card you should get that frequency out from the digital output."

sorry if the questions seems silly but i am a novice in terms of stepper motors and control circuitry. Have i chosen the wrong card or do i need to program in some other way. any suggestions welcome.

thanks.

[kreutz]

This is the answer i got from velleman (usb interface card) forum.

"The PWM output frequency is fixed and you can't control the stepper motor speed by changing the pulse width.

The state of the digital outputs can be changed every 20ms. So the maximum step rate is 25Hz. If your C code is properly controlling the card you should get that frequency out from the digital output."

sorry if the questions seems silly but i am a novice in terms of stepper motors and control circuitry. Have i chosen the wrong card or do i need to program in some other way. any suggestions welcome.

thanks.

Your interface card is limiting your step rate.

It is true you can't control the stepper with the pwm output. 1 step pulse every 20 ms is extremely slow. Why don't you use the parallel port for interfacing to the stepper driver?. You can get more than 40 Khz step rate depending on your PC.

[brijkalani]

Your interface card is limiting your step rate.

It is true you can't control the stepper with the pwm output. 1 step pulse every 20 ms is extremely slow. Why don't you use the parallel port for interfacing to the stepper driver?. You can get more than 40 Khz step rate depending on your PC.

Thanks Kreutz,
got the concept right. the only reason to use a usb board was to keep it simple and get the system working as soon as possible. Also I am using lot of inputs from infrared and other sensors. And I might need to add more steppers. I thought using usb would be easier as it can be expanded to enough number of interfacing boards and easier to control everything from a single program.

But I wont mind changing if i can get a better option. suggestions and recommendations welcome. correct me if i am wrong.

thanks
Brij

[kreutz]

Thanks Kreutz,
...Also I am using lot of inputs from infrared and other sensors. And I might need to add more steppers.

Brij

Exactly how many inputs and motors?, What kind of inputs, digital or analog?
if you are using digital inputs, are they serial?, what baud rate or bps? or just slow speed signals like detectors (one bit)?

[brijkalani]

Exactly how many inputs and motors?, What kind of inputs, digital or analog?
if you are using digital inputs, are they serial?, what baud rate or bps? or just slow speed signals like detectors (one bit)?

I would be controlling 4-5 stepper motors(i am not after very high speeds thou). Analog sensor would be like infrared ones within the range of 0-5V. And digital ones are slow speed signals like detectors. The steppers are to be controlled as a whole system according to the sensor inputs.

Thanks.

[kreutz]

I would be controlling 4-5 stepper motors(i am not after very high speeds thou). Analog sensor would be like infrared ones within the range of 0-5V. And digital ones are slow speed signals like detectors. The steppers are to be controlled as a whole system according to the sensor inputs.

Thanks.

There are some alternatives, keep on using the USB board for data acquisition and using the parallel port for motor control. You only need two pin to control each motor (step and direction). You can use one DIY PC interface card, like the ones in Pminmo site, and the same number of stepper drivers as the amount of motors you want to use.

Or use a motion control PCI board and a PCI Data acquisition board, both are expensive.

[brijkalani]

There are some alternatives, keep on using the USB board for data acquisition and using the parallel port for motor control. You only need two pin to control each motor (step and direction). You can use one DIY PC interface card, like the ones in Pminmo site, and the same number of stepper drivers as the amount of motors you want to use.

Or use a motion control PCI board and a PCI Data acquisition board, both are expensive.

Hi,
As i want it to be up and running I think buying it assembled would be right for me instead of DIYing as shown in Pmnimo(excellent site thou!!).

I found the following card http://www.amplicon.co.uk/dr-prod3.c...10140.htmwould
fit within my budget and has enough digital outputs to control the stepper motors. They said that it has a speed of 2KHz which means around 1000 cycle per sec is considerable speed for my application. I am planning to use my old k8055 usb card for acquisition of data from infrared sensor.

comments and suggestions welcome. please correct me if i am wrong.

Thanks in Advance.
Brij

[kreutz]

They said that it has a speed of 2KHz which means around 1000 cycle per sec is considerable speed for my application.

I don't know your application but 2 Khz is not enough for most of the applications I have seen. there are 4 steps per full step in Full-Step mode, so 2000 / 4 = 500 full steps, divide 500 by the amount of full steps per revolution of your motor and multiply the result by 60 in order to find maximum rpms.

Driving your motor in full step mode is not going to be smooth... and will show a tendency to resonate.