Don't let it nag you, I didn't consider it to be rude at all. Just to the point and i happen to appreciate that.

About loosing steps; I had that before too, with the cheaper drivers at lower voltages. But once I put 24V on it, loosing steps seemed to be gone or at least reduced to hardly noticeable. Later today I will put a part of my findings about voltage, current and the influence on the stepper power here. Now first some FOOD!

 

Yup,
but i will not change that...anymore.
Hopefully by the next week my new big mill will be up and running - ess.smoothstepper, Benezan BOB, 2 out of 3 quality nsk and thk ballscrews in skf quality bearings and best of all: Clearpath servos.

Flo

 

And I hope you let us share in the fun? Will be interesting to see what you have put together this time.

 

I have 11 minutes before Yosemite is ready with installing, so here I go.

The theoretical maximal possible power of my stepper motors (Nema 23 170 oz-in, 2.8A, 2.5mH inductance) is 141.7 Watt. How do I get that number?

According to Gecko the optimal voltage to drive your steppers is calculated by 32*(root of inductance). This gives me 50.6V. To arrive at the power in Watt I calculate 50.6V *2.8A=141.7 Watt. This is the maximum possible power for these stepper motors. So I take this as a start point for further calculations.

My stepper drivers are limited to 50V maximum. With the use of a 48V PS that has a +/- 10% deviation I'm forced to tune it down to 45V to allow for that deviation. (Thank you Jonny for letting me know that is possible to do!). So that limits the voltage for operating the stepper motors to 45V. This will influence the theoretical power of the stepper motors, that becomes now 45V * 2.8A=126 Watt.

The same stepper drivers have a setting for either a PEAK current of 2.84A or 2.37A with respectively 2.03A RMS and 1.69A RMS. The 2.84A is too high so I have to take the next step down, 2.37A PEAK with 1.69A RMS. This will give me a new theoretical maximum power for this setup of 45V * 2.37A=106.7 Watt PEAK power and 45V * 1.69A=76.1 Watt. So with this setup I lost already 46% of the theoretical power of the stepper motors.

This remaining power is available if and when the stepper driver is set to 1 step. But if we take the decrease of power that comes with increasing micro stepping it looks like this;

1 full step setting = 106.7 / 76.1 Watt (100%)
1/2 micro stepping = 75.6 / 53.8 Watt (70.71%)
1/4 micro stepping = 40.8 / 29.12 Watt (38.27%)
1/8 micro stepping = 20.8 / 14.9 Watt (19.51%)
1/16 micro stepping = 10.5 / 7.2 Watt (9.50%)

If I would use a 36V PS for the same setup the outcome would be;

1 step setting = 85.3 / 60.8 Watt
1/2 micro stepping = 60.3/ 43 Watt
1/4 micro stepping = 32.7 / 23.3 Watt
1/8 micro stepping = 16.7 / 11.9 Watt
1/16 micro stepping = 8.1 / 5.8 Watt

So, operating the same setup on 36V as opposite to 45V will result in a power loss of about 20%. On 24V it will be 47% and on 12V 73%. Imagine you operate this setup at 12V, all you have left with 1/16 micro stepping is 27% of the initial 106.7 / 76.1 Watt, being 28.8 Watt PEAK power and RMS of 1.9 Watt. To me it's obvious that with that low voltage and RMS power you're going to loose steps. It's anyway amazing how little is left of the original 141.7 Watt in the beginning. Only 5% at 45V and even 4% on 36V!!! WOW!

(Yosemite is installed!). Back to the iMac now.

About the current being divided over the phases of a stepper motor; most drivers specs state the given maximum current (PEAK) is per phase. If I understood Florian's explanation correct, this current is alternating (right expression for this?) over the phases to make the stepper motor turn. Something like A B A B A B. It is exactly what I've seen while measuring the current to my stepper motors. But I can understand that if, like me, you see only about 1.5A on 1 phase and also 1.5A on the other, while you expect to get 4.5A (if that was your setting) you might think together it is 3A what would be more in line with the expectation you have from the measurement. In my case, if the 2 were added together it most likely would result in burned stepper motors (remember they are 2.8A max!). They didn't burn though. Not even getting hot.

The only way I see to get the maximum out of these steppers, is to tune the PS to around 46-47V, because a little more voltage than 50.6V will result in slightly more heat development in the steppers and I guess that won't kill them immediately. Use a stepper driver that can handle more than this 50V limit and keep the micro stepping down to 1/4 or if possible to only 1/2 step.

About the noise with lower micro step settings I figured that this has much to do with the acceleration settings in combination with the speed settings. With low acceleration and speed there are relatively "few" pulses going to the steppers and this will make it possible to "hear" the steps clicking/rattling. If speed and acceleration is increased the sound and movement will appear more smooth to the operator. The down side of this is, that with a 3mm belt and 20 tooth pulley (1 rev is 60mm) 1 step is 0.3mm and 1/2 step 0.15mm. It gives not much room for error of the machine. Loosing a step or two is going to be visible in the work. 1/4 micro step at 0.075 might be more forgiving and less easy to detect.

You might be right of this setup exceeding the strength of the OX frame. It would be nice if Mark and/or crew could jump in at this point and tell us what the OX (small and large one) can handle qua power.

An other point of interest is how much power is needed to cut wood/metal/aluminium etc.? I've been looking for it for some days now but I couldn't find a useful answer. The only thing I found was a rough estimate of 30 lbs to move a router bit through wood. But no speaking of what kind of wood. Hard wood, MDF, Pine?

So, anybody here that has knowledge about the work force needed to cut these various materials? Maybe some formulas or calculation examples to get me on the way?

 

Think you have made a error in your motors rated power, typically a 4.5a motor is rated at around 110-130watts, a 2.8a is more like 20-30watts.

I know that's not peak watts, but I'm pretty sure a motor rated between 20-30w isn't going to like 141w.

 

I've seen them rated in oz-in/Kg-m etc. but not in Watt. Can you give a link to a motor with that type of rating?

 

This will give you an idea:

http://www.linengineering.com/BLDC-Motors/BLDC16-NEMA17.aspx

And below a link clearly outlining the 48v psu is non compatible.

http://www.cnc4you.co.uk/600W-PSU-48Volt-12Amp

So ignore what I said earlier about the pot. I hadn't realised that they are slightly different to the dsp drivers I have running at 48v, I assumed they were the same but obviously not.

So going off those figures, now you see how 24v gives them ample power.

 

One link refers to a BLDC motor, which seems to be a little different from an ordinary stepper motor. Looking on their site, for Nema 23 1.8 degree steppers they give the rating in oz-in and N-m. The other link refers to a PSU that is not compatible with their own CW 5045 steppers.

That still doesn't show why 24V would give more power to a given type and model of stepper motor than 48V.

I would really appreciate it if you would come with some more substantial and to the point arguments that are "scientifically" verifiable. This information is to me in the given context totally useless to be honest. It doesn't apply at all to the steppers, drivers and PSU I have mentioned before. A bit like comparing apples with pears.

It's nice that you want to help and give advice, but I don't have the idea this is going to help me any further.

Do you have anything on the subject of work force to be applied to wood cutting with a CNC router? Like how much force is needed to push a spinning router bit thru a piece of wood and if possible have some formulas or calculations to work that out?

 

Thanks Mark! Unfortunately I have no android devices, so cannot use that one.

Speeds and feeds I start to understand a little bit by now. My quest is however to find the work forces needed for milling in wood/metal/aluminum etc. so you can estimate/calculate the power needed of the stepper motors to do the job fast and good.

There must be something out there!!!! Just can't find it somehow. Wrong search terms?

 

Sorry Have I missed something, you said they were the same as the wantai drivers?

 

Hi,
maybe you mentioned it but how did you meassure? Did you block them till standstill?

greets

flo

 

They seem to be the same. Specs are very much the same, they even use images from Wantai in their documentation. If you carefully read the specs of the PSU and the CW5045 driver, you see immediately why they are not "compatible". I know why they stated it that way, but saying it out loud could make some people feel insulted.

 

No, I was measuring the phases while the machine was doing air cutting. I never got to measuring while doing real cutting, because my controller started to smoke! Which, by the way, had nothing to do with the drivers or steppers. Just an earth cable not connected to the PS of the controller. Oops!

Most likely I will see higher currents when it is doing real cutting and meets resistance of the material?

 

Have to remain a mystery that one the only difrence between the 36v which is compatible and the 48v according to the datasheets is the voltage, wattage and amps.

The ruling factor being the voltage

 

Actually i am not firm about that.
But surely they need more amps when loadet.
Another possibility would be that they pull most when holding or running at very low rpm..
I will try to find out..

greets

flo

 

Are you trolling me or do I speak/write in Chinese? What is so hard to understand?

 

your drivers mate, I felt I inadvertently gave you the idea you can run them with a 48v psu, an error on my part. That was all. But it seems you have made your mind up.

Good luck

 

those clearpath servos seem pretty cool!

 

https://www.facebook.com/dany.daigle.75/videos/10153589458863623/

Does anyone know how to share a video from Facebook here?

 

oky round 2 of my build got all my stepper motors today and all the goodys with it how is it looking for a beginer hehehe.

 

I have sketchup make witch is the free version now what do I get for the free version to tell the machines what to do and yes its got to be free lol this is my first cnc machine .That way i can reasearch .

 

thank u very mush

 

tryed to get it and its not free

 

http://www.openbuilds.com/resources/sketchucam.1/

SketchUCam is free plugin written for the Google SketchUp CAD program that allows the creation of Gcode to control your cnc machines and bring your SketchUp creations into the real world

 

If you use Google Chrome, or don't mind downloaded it. You can easily emulate Android apps with this Chrome extension.

http://goo.gl/gAn0Xh

I extracted the APK myself, download it here.

https://www.dropbox.com/s/dtcqmte7lr5rg3f/CNC Force Calculator Free_1.00_1.apk?dl=0

Seems to work best selecting landscape mode, phone mode. Works the same as if on a android phone.

Note: Arc Welder, the extension that allows you to load android programs, only allows one apk loaded at a time. So when you launch it again, select remove to remove the previous instance and proceed with the new one.

Also can use a program called Bluestack.

http://www.bluestacks.com/download.html