Build Thread- microCarve A4/Gecko G540

[saundby]

I've got all three motors wired and checked out now. EMC2 is happily driving them through the Gecko G540 on my bench top. All the currents and temperatures look normal for motors running with no load.

Now to start assembling the microCarve A4 itself. Hurray!

My promised pics got delayed by my daughter borrowing my camera. I've got it back now. The battery is dead, of course. It's on the charger.

I'll be getting some pics up later.

For now, more building, less posting.

[jjacstcy]

Thanks saundby for the help. I came up with .048 watts. I ran it for awhile tonight and everything seems fine. Like I said thanks againg for the help. Nice looking telescope by the way!

[saundby]

Originally Posted by jjacstcy Thanks saundby for the help. I came up with .048 watts. I ran it for awhile tonight and everything seems fine. Like I said thanks againg for the help. Nice looking telescope by the way!

Thanks! It's been a great scope. For about 10 years now I've been showing people the sky through that scope. Literally more than a thousand people a year get to see various astronomical objects through that scope, each year since I built it.

Glad to hear the current is plenty low!

[saundby]

Things went really well today. I've done a first pass at assembly on my A4, I'm sure some tweaks will be needed, but everything is together now.

Tomorrow I'll be hooking up the controller and computer and do some testing without a spindle attached. Once I feel like I've got the barest clue that I'm running things properly, I'll see about getting a spindle attached. Which will involve me constructing a mount for it, but otherwise everything will be ready.

The pics:


Here's the back of the controller box, as completed. The fan cutouts are where some small airflow slots used to be. The bottom one was my first go, the upper one is a later better version. If I decide I need more airflow after I've had the motors running under load, I'll cut out the crossbars on the lower cutout later.


The front, looking just like it did originally. I'm going to put some custom stickers over the Emerson ones later. For now, I've got a big red switch that goes "ker-chunk" and an LED power light.


Here's the microCarve A4 fully assembled without motors. Later, I'll be posting a step by step guide with the assembly procedure I hit on as probably the best (on my third try. It wasn't much trouble, though. I was expecting to sort of feel my way through the process and it was fun.)


Here it is with motors mounted. I managed to steal a little time after dinner before an evening with the family to get this far. Tomorrow I'll bring the motor controller and computer out to the garage and start spinning leadscrews!

-Mark

[microcarve]

Well, I'm just Amazed at how good everything looks!

Beautiful work!



Thanks Very Much for the pictures!
I can't wait to see more...


John

[saundby]

Well, I brought my controller and computer out into the garage, hooked them up to the motors. Then, while I was manually moving the motors one at a time from the computer's keyboard to make sure the motors were plugged in to the correct axes, the motor I was running stuttered a bit, then the DC power went out.

When I troubleshot it, I found that the DC power supply comes up to its peak output voltage then shuts down practically immediately. Because there's no load (everything's disconnected) it takes 30 seconds or so for the voltage to bleed off to zero. The power supply's LED stays lit, but the output is shut down.

Just for point of reference, I ran the motors pretty extensively on my desktop before hooking the up to the leadscrews. I ran them through a couple of programs, no problems.

Now they're on the leadscrews driving the slides. There's no spindle, and no binding on the axes. I can turn the motors easily by hand.

The power supply is a Keling KL-350-48. I thought it was unregulated when I got it, but a look at the link at the top of the Keling power supply page (http://kelinginc.net/Listofpower.pdf) has it listed as regulated.

So, a wild guess based on my experience repairing power supplies is that maybe the motor+leadscrew generated back-EMF which blew the regulation of the power supply?

The motors are presently wired series bipolar. Would a change to parallel bipolar (or unipolar) help prevent this problem (whatever it is)?

Also, I've got a 24VDC 10A supply on hand. I'm thinking of using this until I sort out the other supply. It's within the 4 to 20x voltage range for my motors, does this sound reasonable, and if so what steps can I take to reduce the chances of a repeat performance with this power supply if I wire it up? Or should I look at a different supply setup?

TIA

-Mark

[eaglezsoar]

Mark, that power supply is rated as a 7.3 amp 48V switching type. Are you sure that 7.3 amps is adequate for your application?
I try to avoid the switching type supplies, there is just too many parts that can fail. There are a lot of the switching type supplies running
CNC; I doubt that back EMF destroyed your power supply. You indicate that all worked fine until your motors were placed under load
by being attached to the lead screws, this seems to point to inadequate current either by the power supply being defective or the output is too small.
Bipolar Series gives very good low speed torque. But because of the high inductance, the torque drops off rapidly.
Bipolar Parallel gives good low speed performance and its low inductance allows the torque to be held out to high speeds. But we need to increase
current by 40% to get those advantages. Changing to unipolar would require new drivers and I see no advantages to do that.
Using your 24V power supply may be a simple way to see if your other supply is defective. Now I know why I like the humble toroid transformer and rectifier, there
are less parts which means less problems but you must size any supply for an output that is more than what is needed, simply because you need a little overhead.
Best to you Mark and great job on assembling the machine with such a nice paint job.
Regards,
Carl

[saundby]

Thanks, Carl!

Your clear explanation of the tradeoffs of the different ways of wiring the motors is just what I was looking for on that. It sounds like bipolar series is within bounds for what I want in performance right now. I may change to parallel later if it looks like it'll give me some advantages in use.

It's possible that current was the cause of failure, but there are some things that made it seem unlikely when I was troubleshooting. The unit didn't generate any significant heat, for one thing. Also, when it initially shut down it would come back after a short while switched off. I disconnected the motors and switched it on--it would run at 48V for a short while, then shut down as I described. Of course, this was after the initial event, so it may already have been compromised.

Also, a current failure should keep it from being able to produce a high output voltage. It comes up to peak output (about 51V) when powered on, then cuts off. Which sounds like a regulation problem.

Still, without a schematic and a real knowledge of the circuit, I'm just using a dowsing rod.

I agree on the linear unregulated vs. switching supplies for this application. I was under the impression that, at worst, I was buying a linear regulated supply. Since it's in a can, I didn't see the insides to know the difference and the weight was light but things have come a long way since the days of boat anchor transformers so that didn't clue me, either. *shrug*

At any rate, I think the long term solution will be to replace this supply with an unregulated linear, as you recommend.

If I do hook up the 24V supply, I'll monitor current until I see what sort of a draw I'm getting, and hook up one motor at a time. That'll give me more information on what I'm doing, too.

Edit: I should probably also note that I've got the Gecko set up with motor current resistors, 2.2K on each of the three motors. I measured each one before installation and selected ones closest to 2.1K I could, so I at least know that there aren't any that aren't in the correct range. At any rate, this should mean that the Gecko is putting out a max of about 6.6A. Exactly how that relates to what it draws is something else, of course, which I'm still looking into.

Latest as of 5:45PDT 4/11: More data. John from Keling asked me to check the fuse. I popped the power supply open and pulled the fuse. Zero ohms. The fuse is still intact. Also, there's no sign of component damage inside otherwise.

More news: Probably just a bad power supply. John at Keling will refund my money on this one when I send it back. I'll be ordering another supply (from Keling, I expect ).

[saundby]

I've ordered a 38V 15A unregulated power supply to replace my prior power supply. The current is overkill for what I need right now, but it was the closest to what I wanted that's over where I expect to be when I add a fourth axis to this CNC. It'll still be overkill then, but I sure won't have to worry about having enough.

Hopefully I'll have it by this weekend and be up and running then.

In the meanwhile, I'll be making a spindle mount in whatever spare time presents itself, so that I can go from dry runs to cutting quickly. I'll be starting out with a cheapo spindle so I won't be out too much when I drive it three inches into the table top.

-Mark

[saundby]

I finished the spindle mount this weekend, it's a simple affair to get started. I'm going to be making my first cuts with the machine this morning, assuming my initial "cuts" on air go well.

I'm using an inexpensive Harbor Freight router as a spindle. I mounted it on the Z-axis with a piece of plywood for a baseplate and a pair of muffler clamps to hold the router body. I've placed some strips of inner tube rubber around the router's body to help the grip the clamps have on the router without having to gronk down on the U-bolts too hard.



Now to actually try cutting some material...

-Mark

[saundby]

OK, cutting air showed me I needed to do some additional adjustments to the software (invert the Z and Y axes), then I grabbed some scrap plywood and mounted it. The piece I cut on top has wood screws holding it from underneath.

I converted an image file to a rasterized cut, so the bottoms of the cuts aren't as clean as they would be using real CAD/CAM to guide the router to cut the shapes of the letters and all. Basically I just grabbed what was at hand to do a quick and dirty job here.

The depth of cut is 1/8", the material is some old, somewhat dry birch plywood recovered from a failed project. The bit is 1/2" 90 degree.





Edit:

Here's the results of my second go. A bit more complex pattern. I spent way too much time trying to tweak the gcode before the run, so that's all I've got to show for the day. It's also time to get a finer bit.

[saundby]

I started learning gcode yesterday to use my A4 more efficiently. Here's the result of my first gcode program:



The full story is on my blog:
Learning GCode with EMC2