Stepper motor for Taig CNC mill

[bramlego]

I'm planning a CNC Taig setup. Based on the threads I've read here, the Gecko 540 is the way to go. Here are the two setups I'm considering:

1) (based on this)

KL23H256-21-8B 3.0A, 2.4mH, 185oz-in $28 on X, Y
KL23H276-28-4B 2.8A, 3.6mH, 270oz-in $39 on Z
Total: $95, 5.9A

2) (based on this)

KL23H2100-35-4B 3.5A, 2.8mH, 381oz-in $49 on X, Y, and Z
Total: $147, 7.0A


I have seem a 7A fuse mentioned for the Gecko before, but their own website shows testing with 4x 3.5A motors and a 9.3A supply. Will the current over 7A ever get used?


Will option 1 run at higher rapid speeds? What about cutting speed? If you have a setup with lower torque motors like this, have you ever run out of torque (while cutting steel or something...)?


Is option 2 overkill? Or is the extra torque useful (and worth the extra $52 + extra $$ for a bigger power supply)? I would like to leave room for expansion to a 4 axis setup.

Thanks for your input!

[Jeff-Birt]

You are absolutely right about the fuse, the G540 will never, ever draw more than 7A. That being said properly sizing the power supply has a lot to do with the type and quality of power supply you are using. If you use a linear unregulated supply you need to 'oversize' it about 30% so that its output voltage remains at an acceptable level while under load. If you use a good quality switch type supply it should be able to put out its rated current and rated voltage with no problems.

You do not need/want big steppers on a Taig. I use/recommend steppers about 166 oz-in. I have been using this type of motor on Taig systems for quite a while now. Since the Taig has a 20 TPI lead screw the acceleration and velocity of the motor are more important that gobs of torque. Here is a short video of my 'little' motors running my Taig mill at 90 IPM.

[nomedia="http://www.youtube.com/watch?v=RzrBcXCNDhU"]YouTube- 90 IPM SS[/nomedia]

[rowbare]

The KL23H276-28-4B 2.8A, 3.6mH, 270oz-in isn't a good match for the G540, a much better match in that size range is KL23H276-30-8B 282oz-in.

Using the formula 32 * sqrt(inductance) which Gecko recommends for calculating motor voltage, the 270 has an inductance of 3.6 mh and wants about 60 volts. The 282's inductance is 2.2 mh which works out to a voltage of 47.5 volts. This matches well with the 185's 2.4 mh (49.5 v).

Jeff's advice is spot on btw. I am currently using 282s on X and Y and a 387 on the Z. I will be switching to 185s on the XY and either a 185 or 282 on the Z (I bought 4 of each size a while back to experiment with...)

bob

[bramlego]

But KL23H276-30-8B draws 4.2A/phase in bipolar parallel mode...
so on the Gecko it will only run at 235 oz-in instead of 282, right?

Are you sure it's a better fit than the KL23H276-28-4B?

[rowbare]

But KL23H276-30-8B draws 4.2A/phase in bipolar parallel mode...
so on the Gecko it will only run at 235 oz-in instead of 282, right?

Are you sure it's a better fit than the KL23H276-28-4B?

You made me think there! I had forgotten why it was a better choice. I based my reply on this post by Mariss from Gecko: g251's w/SS BoB or g540

You are right that by derating the current, you give up a bit of holding torque at the lower end but the dynamic performance of the 282 will be better because of the lower inductance. For a given voltage, a motor running at 3.5 amps will put out more power than a motor running at 2.8 amps. To paraphrase Mariss, power makes chips, holding torque doesn't.

Jeff's experience bears this out. He gets insane speeds and outstanding performance out of the tiny motors he is using.

bob

[Jeff-Birt]

Jeff's experience bears this out. He gets insane speeds and outstanding performance out of the tiny motors he is using.

The moral of the story is not to listen to the little voice in your head that says bigger-is-better. Don't just run out and buy the biggest motors that a particular drive can handle. A set of good quality, matched components will always work better.

Since the mechanical bits of the drive on the Taig are already in place the trick is to match everything else to the machine.

[bramlego]

For what it's worth, here is my comparison of the 185oz-in Keling motor and the 166 oz-in motors Jeff is using. They appear to be very similar motors.

I took the torque/speed curves for the 166 oz-in motor at 32V and the 185 oz-in motor at 30V. I detuned the speeds for the 166 by 30/32 so the voltages would match. The thrust I calculated using T=kdF where
k=0.1 for a bronze nut on a steel leadscrew
d=0.5 for the Taig leadscrew diameter
T is the motor torque
F is the thrust
This doesn't take into account any other inefficiencies besides the leadscrew of course. The speed I calculated using 1.8 deg/pulse and 0.05 in/rev (Taig leadscrew pitch).

[dkp_design]

You are absolutely right about the fuse, the G540 will never, ever draw more than 7A. That being said properly sizing the power supply has a lot to do with the type and quality of power supply you are using. If you use a linear unregulated supply you need to 'oversize' it about 30% so that its output voltage remains at an acceptable level while under load. If you use a good quality switch type supply it should be able to put out its rated current and rated voltage with no problems.

You do not need/want big steppers on a Taig. I use/recommend steppers about 166 oz-in. I have been using this type of motor on Taig systems for quite a while now. Since the Taig has a 20 TPI lead screw the acceleration and velocity of the motor are more important that gobs of torque. Here is a short video of my 'little' motors running my Taig mill at 90 IPM.

I know this is an old post, but I'm fed up with my taig. I have Xylotex 3axis board, Xylotex 267OzIn steppers running (2.8A) full step, 24v regulated power supply and Xylotex Vref is maxed at 2,5A Ways are smooth and no real drag. But All I can get is 23IPM Rapids. Mach 3, And lately, I am loosing it on Y, which is my smoothest Way as well.
What motors and drive do you suggest? I'm looking on Gecko but still confused. Most theres are 10uStep I see, but doesnt microstepping loose Power? It does with my setup anyways. I am producing parts (I know, Taig hobby) But it is a hobby and selling these parts for my other hobby. But 90IPM would help me greatly. presently cutting 20IPM, 1/4" 4flt in alum, 2nd form top pully

Any help would be appreciated. I'm sure I need to spend $ Just where and on what?

[LaserImage]

I built a cnc router a few years ago and used a 24v power supply and a cheap board. I had troubles getting anything over 25 ipm without losing steps. I fought it for a long time trying everything I could to get more consistency. Finally, I bought a G540 and a 48v power supply - what a difference! I was getting 120ipm rapids and it never lost a step. I moved this setup to my Taig when I bought it and it is performing just as well, although not quite as fast, the Taig is much tighter and is heavier than the router, but it's plenty fast enough to be a production machine if I wanted it to be.

So, my suggestion would be to go with a G540, 48v power supply and the proper steppers - you can't go wrong with this setup!

Gary

[awerby]

Like the previous post implied, your problem isn't the Taig, it's that Xylotex control and the ridiculously mismatched motors that someone apparently sold you with it. Motors with a lot of holding torque like those have a correspondingly high inductance, and need higher voltages to run fast. With a 24 volt max on your controller, it's a wonder that setup worked at all. Go with Gary's suggestion and you'll be amazed at the difference it makes.

Andrew Werby
www.computersculpture.com

[dkp_design]

OK, Any difference in the G251X over the 540? I only need 3 axis. I see there cheaper.

[dkp_design]

And what size power supply? Do I add up all 3 steppers current plus a little bit?