[mocnc]

Ok, I have been making my own cnc for sometime now, and I have reached the spot were I need to choice which driver board. I am wanting to make a 4 axis cnc, the 4th being a turning type axis. I am leaning towards the hobbycnc 4AUPC Chopper Driver Board. Now......first question is what is the difference in polar and unipolar, and I am not sure what the Chopper stands for. I hope those aren't first grader type questions, if they are I am sorry for asking, but would appreciate any and all help. My next question is the most important for me. Which driver board are you using and why? I know there is the gecko boads out there as well and a few more others. But would love the input, good or bad for the boards that you like or dislike. My main choice for the Hobbycnc board is its price......$115 USA, not bad at all. But that will not be the only reason why I will buy that one, i am hoping to get more info from ppl here with the knowledge of some of the boards.

[Chris D]

Ok, I have been making my own cnc for sometime now, and I have reached the spot were I need to choice which driver board. I am wanting to make a 4 axis cnc, the 4th being a turning type axis. I am leaning towards the hobbycnc 4AUPC Chopper Driver Board. Now......first question is what is the difference in polar and unipolar, and I am not sure what the Chopper stands for. I hope those aren't first grader type questions, if they are I am sorry for asking, but would appreciate any and all help. My next question is the most important for me. Which driver board are you using and why? I know there is the gecko boads out there as well and a few more others. But would love the input, good or bad for the boards that you like or dislike. My main choice for the Hobbycnc board is its price......$115 USA, not bad at all. But that will not be the only reason why I will buy that one, i am hoping to get more info from ppl here with the knowledge of some of the boards.

I am using the HobbyCNC board on my router and it works good and is inexpensive to boot! I also have one of their 200 oz-in steppers and it too performs good.

Chopper is a current control "Device" that limits the current to the motors when you run them at higher than nameplate voltate for increased performance. It is a "Good thing" to have.

I will let others explain the uni-bi polar as I really can't say with any confidence.

It would help also if you could specify what size machine you have and what you plan to cut etc. Also, what are your expectations of the system (cutting performance etc.).

Chris

[sdantonio]

There are no first grader questions

UNIPOLAR

The name unipolar is derived from the fact that current flow is limited to one direction. As such, theswitch set of a unipolar drive is fairly simple and inexpensive. The drawback to using a unipolar drivehowever, is it's limited capability to energize all the windings at any one time. As a result, the number ofamp turns (torque) is reduced by nearly 40% compared to other driver technologies. Unipolar drivers aregood for applications that operate at relatively low step rates.

BIPOLAR CHOPPER

Bipolar chopper drivers are by far the most widely used drivers for industrial applications. Although theyare typically more expensive to design, they offer high performance and high efficiency. Bipolar chopperdrivers use an extra set of switching transistors to eliminate the need for two power sources.Additionally, these drivers use a four transistor bridge with recirculating diodes and a sense resistor thatmaintains a feedback voltage proportional to the motor current. Motor windings, using a bipolar chopperdriver, are energized to the full supply level by turning on one set (top and bottom) of the switchingtransistors. The sense resistor monitors the linear rise in current until the required level is reached. At thispoint the top switch opens and the current in the motor coil is maintained via the bottom switch and the diode. Current "decay" (lose over time) occurs until a preset position is reached and the process startsover. This "chopping" effect of the supply is what maintains the correct current voltage to the motor at alltimes.

CHOPPER BOARD

This refers to having a built in power resistor on the driver board. Lets say that your power supply provides 35VDC at 10 amps. If you'r motors require 2.5VDC at 2 amps then you somenow have to adjust your potential difference downward to 2.5VDC to avoid burning out your motors. This is done either by a seperate power resistor placed between the driver board and the motor, or if you have a chopper board, it is built into the board (usually a trimpot) and adjusted before your initial startup of the system.

check out http://pminmn.com for some very sweet board designs. The like is also in the open source section here (in the event that I remembered the URL incorrectly). Phil is extremely helpful if you have questions on his stuff. If your good with soldering them Phils stuff is probably much better than the hobby CNC boards. Also Phils boards are mostly modular which makes troubleshooting easier (and cheeper if you have to rebuild a whole board). If you don't trust your soldering then look for some xylotek bipolar boards.

Steven

[sdantonio]

Stuff I forgot.

4 wire motors are unipolar
5 wire motors are bipolar
6 and 8 wire motors can be wired as either bipolar or unipolar. But wiring the motor unipolar you loose about 30 to 40% or your motors peak holding torque.

boards and motors can often be found on ebay cheeply too.

Steven

[sdantonio]

http://pminmo.com/ is the correct URL

Steven

(OK, I'm done posting for now... switching off my computer and going home)

[Madclicker]

Stuff I forgot.

4 wire motors are unipolar
5 wire motors are bipolar

Steven

Is this really correct?

[ger21]

The drawback to using a unipolar drivehowever, is it's limited capability to energize all the windings at any one time. As a result, the number ofamp turns (torque) is reduced by nearly 40% compared to other driver technologies. Unipolar drivers aregood for applications that operate at relatively low step rates.

The HobbyCNC is a unipolar Chopper drive. It doesn't have any problems running at higher speeds.

Chopper is not a resistor on the board. It's a method of regulating the current by turning the voltage on and off very quickly.

And 5 wire motors can not be used with bipolar drives. A bipolar drive has 4 terminals, and can use 4, 6 and 8 wire motors. Unipolar drives will work with both 6 and 8 wire motors.

With the HobbyCNC board, and a 6 wire motor rated at 200 oz-in, You'll get the full rated torque from the motor. With an 8 wire motor, however, if the motor's rated torque if for bipolar wiring, you'll lose about 30% of the rated torque.

[sdantonio]

Thanks, I realized I had gotten the 4 and 5 wire drives backwards while I was driving home. I knew at least several people would catch that. It's good to have proofreaders.

Steven

[spalm]

I agree with the posts so far. Just thought I’d try a different approach. Motors need to have their current controlled. Jeff summarized what happens in a motor in one of his recent posts. You can use either a resistor or a chopper to control things.

A chopper is kind of like a light dimmer. It is very quickly controlling things. If you wanted to dim a light, you could put a series resistor to limit the power to the light. The light would dim. The problem is that the resistor would consume the power instead of the light and that power would become heat instead of light. Heat is nice sometimes, but not what we want here. Notice that a modern light dimmer does not get hot. This is because it uses solid state electronics to switch the power on and off on every sine wave. If you would look at the waveform it would look more like a saw tooth instead of a sine wave. Since the bulb is not getting the full sine wave, it will dim. The disadvantage is it is more complicated and the light bulb will ‘sing’ because it is not getting the smooth sine wave that it was designed for. Motors driven with a chopper will also make an audible hiss.

The hobbycnc and Xylotex both use the Sanko motor driver chip. It has all the chopping and feedback control built in. This chip can only drive 3Amps. It will destruct if more than 40 volts is applied. The hobbycnc 200oz motor is a 3Amp motor. Hmmm, a matched pair.

Steve

[sdantonio]

I've been hearing so many people use the concept of a chopper and balasting resistors interchangably I assumed they were the same thing. This is why I have to get out and talk to you EE's more often. It's funny how we all evolve into our own little worlds, I can't point to a single person I know any more and say this person is a electrical engineer (I used to know a few). I turn over any stone and I can find a physicist, but you EE's are scarce. Thanks for the feedback.