3-Axis Stepper Controller

[alberto2]

Dear MP i have built the relay board and it work well, but i have a problem:
mine 3-Axis stepper controller board work at 26.2Volt (20-1.4*1.41) and my electric trasformer(20V 3A) have just one secondary.How can i take 12V to power the relay board and a little cooler fan (12V 2.3W)?
I must buy a little transformer (12v-500mA ex.) to power them or there is a solution from 26v to 12 volt?
???

 

[MP1]

Alberto, you can add a 12 volt regulator to the circuit if you find one that is rated above your output voltage.

Another way to step down the voltage is with non polarized capacitors on the secondary output of the transformer. You connect capacitors in series across the secondary of the transformer to make a voltage divider. If you connect two 100 uf capacitors across a 20 VAC secondary, you will have 10 VAC at the point where the two capacitors are connected in series. You can use different values of capacitors to change the proportion of the divider. In series, the voltage across each capacitor is inversely proportional to it's value. The smaller capacitor has the larger proportion of the applied voltage. Experiment with some values on your workbench. You should find a solution. Don't forget, you are still working with AC, so the voltage will need to be rectified to DC.

MP

 

[GreekPIC]

Ok, I built the circuit and it worked fine. I had only one UCN so I tested only one axis with TurboCNC, other than that it's ready.

Just one question: when the motor is not moving one coil is still energized. This is probably normal and supposed to provide holding torque but the motor is warming up. Is this normal?

 

[MP1]

It is normal for steppers to run warm/hot. You will notice that the motor, when it is not moving, is in a locked position. Otherwise it would not be very good at holding a step.

MP

 

[GreekPIC]

Ok, thanks, I downloaded the motors datasheet and it's good for 24V so no problem. I'm using 12V right now but I have a 18V PS I might use.

Now I have to make the relay circuit to turn the spindle on.

PS. Looking back at the thread I saw I have made a mistake in the coolant discussion. The 220 grade oil is used on the slides and is not water soluble. We use Castrol Superedge 33 (~8% in water) as coolant.

 

[GreekPIC]

Yesterday it worked, today it doesn't! The motor has holding torque but is not moving. What could that be?

 

[MP1]

Can you post the schematic? Or did you use the one in the projects section for this chip?

MP

 

[GreekPIC]

I used the schematic from the projects section. I didn't change anything between the two runs. The voltages are ok.

Only thing I can think of is that the IC burned. But I only used the circuit for 10 minutes and the IC didn''t get hot (I didn't have a sink so I checked frequently).

I've ordered the rest of the IC's (I tested only one axis), I'll swap this one and see what happens.

 

[MP1]

Usually when the chip goes bad, the holding torque also goes away. How are the pulses on the step pin?

MP

 

[GreekPIC]

I have to check it out. I was thinking that maybe something is wrong with the software (TurboCNC) or the printer port. I'll probably make a 555 based circuit to give pulses for testing.

 

[MP1]

I agree. Both of these items could cause your steps to fail. On the other side of the spectrum, if your pulses are too fast you would get the same result. In this case, all you would need is to slow down the steps in the software. Hope it is a simple fix.

MP

 

[GreekPIC]

Ok, working now. I don't know what was wrong because I changed more than one thing (not good, I know). I increased the pulswidth in Turbocnc, changed the mode to 2-phase (jumpers) etc.

I still have to play with the feedrate settings to see what's the top speed I can get out of it. I also found out that I have to redesign the bearing housings because the gears bind at high speeds. The placement is critical so maybe I'll have to make the housings adjustable.

 

[MP1]

I have noticed that some programs are very dependent upon the processor speed of the computer you are using. In this case, it is trial and error until you find the perfect speed.

Are the bearings manufactured by you or is it something you had to purchase? I was curious about the binding. I have an XY table that I just used threaded rods attached to the stepper shafts and nuts clamped to a mount on the table. There is no bearing on the end. It sits freely in the air and there is never a problem with binding. The weight is supported by slides such as drawer slides. Problem there is finding some which are made well enough to give you whatever precision you are after. You have to find a set that does not have too much play.

MP

 

[GreekPIC]

I use roller bearings in DIY housings (see pic). The problem is that the distance between the motor gear and the lead screw gear has to be set precisely. I decided to ditch this setup, however, for the following reasons:
1. The binding problem
2. I don't need reduction, the motors seem to have enough torque so no reason to loose speed
3. More backlash problems
4. K.I.S.S.
So I decided to go with direct drive.

I received the rest of the UCN's and connected all motors. I also connected home and limit switches and they are working great. Now I have to make the relay board. A question here:
If I make the PNP version won't the motor start if the PC shuts down? I think I'll make the first version.

View attachment 35998

 

[Mikromike]

Hello: I starting to build this 3 Axis controller and was wondering if it

 

[MP1]

If I am looking at the same schematic as you, then C2 is a 10 microfarad and C3 is a 0.01. These are by-pass caps to keep the DC voltage smooth. I recommend that you use the better caps (and the correct values). The only problem you will have if you do not is a little noise in your circuit, which might interfere with the precision of the steps.

MP

 

[Mikromike]

Thanks MP, you brought something to my attention though. The schematic shows C1 = 0.01uF, C2 = 10uF Polarized, and C3 = 0.01uF but the board parts lay-out shows C1 as being polarized. I hope this is NOT a problem, I laid my board out just like the parts lay-out shows, it seems to work. I hooked it up to a 555 signal generator and the stepper motor steps. Also this is my first attempt at making a hobby CNC what software would you recommend and are their any other pitfalls I need to look for when making the CNC machine? My primary goal is to make PCB

 

[MP1]

You should have no problem with the non polarized. I normally use tantalums for this value. I keep quite a stock of them for micros. The larger caps should be polarized ones, though.
There is a cad program out there called DanCad. It might be what you are looking for. I wrote my own but it does not use the standard NC drill format. It uses X.Y coordinates. I had intended to later add a module for the NC drill format, but never had the time to go back to it. If you are familiar with programming you can write your own program. You just send pulses to the parallel port in the form of binary numbers (1s and 0s). The ones are the pulses for the motors.
Here is a tip (a real time saver): Make yourself a small board with LEDs and resistors to connect to the parallel port to test the program before you send anything to your project. You will want to know you are pulsing the right pins before you connect to an actual stepper.

MP

 

[Mikromike]

Thanks for the advice MP...Mikromike

 

[alberto2]

This is a siple way to obtain a very inexpensive CNCmill!
It can engrave metal very well!
What do you think about? i think that it's a good idea!

View attachment 36063