4-axis unipolar kit

[itsme]

Hi everyone,

I've been looking at various boards lately for a small CNC mill and came across the 4-axis unipolar kit from Xylotex. This board seems ideal for me, as the kit is relatively cheap (good when you're a student without a money tree...). I should be able to get it assembled successfully, even with my limited knowledge of circuit board soldering...

I have a few questions about this board though and its operation (assuming I can get one together):

- If I wanted to run stepper motors rated at 4.5V and 2.5A/phase, what kind of power supply would I need to run it? Would I need seperate supplies for the board and the motors?

- How is the current to the motors set and what is Vref?

- Does the board have inputs and outputs for things like limit switches and coolant control?

- Is it generally reliable and relatively simple to setup?

I'm sorry for all these questions, but i have to learn somewhere...

Thanks
Warren

[ger21]

First, it's just recently been released, and I haven't heard of anyone that has used one yet. But his other drivers are very high quality and very polpular.

Power Supply - Just one needed, preferably 24V to 34V, about 6a minimum.

You set the current by adjusting a pot to put out a certain voltage. That voltage is VREF. You'll need a meter to set it up.

It looks like if you add some optional resistors, you're all set for limits. The board is set up for these, but not sure if they are included. Coolant might require a relay, which would not be included.

This is just info I got from checking the website, but should be accurate. If you email Jeff from Xylotex, he'll answer all your questions. He's a great guy to deal with.

HobbyCNC sells a driver that is basically the same as the Xylotex, at http://www.hobbycnc.com. A lot of people are very pleased with that one.

[itsme]

Thanks for the reply, Gerry.

There's one thing that I'm still not sure of. I had a look on the Xylotex site and found a manual for this board. In this manual it says that the current to the motor is 'Vref/0.33' and that Vref can't exceed 1V. This all makes sense, because that explains the maximum current per phase being 3A. What I don't quite understand, is what the voltage to the motor will be. If the motor is only rated at 4.5V, the power supply is giving 34V and the Vref is set at say 0.8V (to give roughly 2.4A for the motor), then where is this 4.5V (approximately) coming from to drive the motor?

Regards,
Warren

[ger21]

Steppers can and should be driven at much higher than the rated voltage. Steppers drivers only regulate the current. By using higher voltages, it allows the current to flow faster through the motor, which let's the motor spin faster.

[itsme]

Thanks again, I didn't realise that the motors could be driven at much higher voltages. Just as a matter of interest though, what exactly is the point of giving a voltage rating to the motor, if it doesn't really restrict it in any way? Does it have anything do do with its resistance by any chance?

Regards
Warren

[ger21]

The voltage is the currrent rating times the resistance of the coils.

[itsme]

Hello again, and thanks for the replies - they really helped.

Can anyone tell me exactly what is needed in order for limit switches to be used. Also, what kind of switch is normally used for limit switches?

Thanks
Warren

[coherent]

The switches use one of the output pins from your parallel DB25. If your driver board has terminials available that gives you access to the pins, it's fairly easy. The Xylotex site has some simple layout schematics for wiring your switches in either parallel or series configerations. You'll need resistors to pull the circuit low and then tell your software your setup so if recognizes when the circuit goes high (or visa versa), so it will stop (if a limit) or reference (if a homeing switch). Or, both if your software is capable.
As far as switches, just some small microswitches will work fine. The kind with a small arm that bumps the switch. Wire in normally closed (NC) so that when a switch opens or a wire breaks, your circuit will make note of the open circuit and stop things.
Do a search for breakout boards... they make things much easier and will protect your computer and provide the necessary resistors onthe board.
Take a look here for info too...
http://www.campbelldesigns.com/breakout_board_plus.htm
and
http://www.pmdx.com/

-marc

[ger21]

Marc, I think he's talking about the Unipolar board, which has provisions for the pull up resistors built in. They may not be included in the kit, but the space is on the board for them. So you don't really need a breakout board with the unipolar board. The schematics on the website (last time I looked) were for the bipolar drives.

[Hawkeye]

itsme,
I have just built this board. It was very easy to build and the instructions are straight forward. if you look at the bottom right hand corner you'll see a set of screw position wire lugs, it is set up for an "E" Stop, 3 home switches and a limit switch (You can Parralell as many as you need). The pull-up resistors are included in the kit.

[Hawkeye]

The only thing I did different was to use wire where the LED was so that I could mount it as an Idiot light after I put it in a case. The second LED is an Idiot light to let me know that I have turned on my power supply.

[Hawkeye]

I also took advantage of the boards feature to mount external enable switches for each axis. I don't know if I'll ever need them, but what the heck....It's cool.

Hope This Helps,
George