[JerryBurks]

I noticed the mention of the morphing feature on the G203V model but did not see it on the G540 or for that matter the low cost G250X or G251X model. I am anyway wondering if the G540 consists of 4 each G250 modules on a master board? The G540 would not help me much anyway since I have the Planet-CNC USB controller that has better in-out functionality.

Oh well, I will probably give Gecko a call today. I was anyway planning to add a rotary axis sometimes in the future and that would give me an excuse to buy some hardware already.

There are two major features of the Gecko drives that others don't have (as far as I know. Some of the newer drives may have caught up by now if patents haven't prevented it). A very effective resonance reduction circuit, and automatic morphing of the step pulses per revolution. The very popular G540 and G203V drives both have this......

CarveOne

[CarveOne]

Both the G250X and the G251X mentions it having the morphing feature. The G250X is a single drive module that you could use as the 4th axis driver. The G203V is a higher current (7 amp) version of the G250 board. The G203V has morphing even though it is not mentioned in the description. Yes, there are four G250 boards in the G540 assembly, plus a simple breakout board circuit.

See red text below:

------------------
The G250 is one of Geckodrive's newest low-price, high-quality step motor drives.The G250 is produced using brand new techniques allowing it to be sold for very low prices in volume while maintaining excellent quality. This is the drive that forms the control interface of the G540 and comes with a 2x15 2.54mm header for a connection.

• 3.5A 50VDC maximum
• Digitally filtered STEP, DIRECTION and DISABLE inputs
• 3.3V and 5V logic compatible inputs
• 300 kHz maximum Step pulse frequency
• Top settable Adjust trimpot
• Power LED indicator
• No user settable jumpers
• 20 kHz switching frequency
• Mid-band resonance compensated
• Microstep to full step morphing at higher speeds
• Small size
  
• Four layer PCB
• Discrete all n-channel MOSFET full bridge design
• 14A rated power MOSFETs
• 2.5mm 2x15 header in either male or female
• Recirculate mode when the motor is stopped, reducing motor heating

CarveOne

[RomanLini]

I'm a bit stumped why your resonance issues are so bad and at such a low speed?

Maybe it's some issue with your particular type of stepper driver? Some drivers require a large PSU cap on their power terminals, I have some old driver modules here that don't say anything on the module but it is mentioned in the datasheet; they need 2200uF adding across the power terminals close to the module. Which is pretty good advice for most stepper drivers anyway if they need to do higher speeds. Your large motors may even need 4700uF. Since a 2200uF 63v cap costs about $2.50 it's probably worth trying as a test before you buy new drivers.

Also are you trying to run the motors continuously at that particular resonant speed? It's best to just accelerate through that speed reasonably fast. Even a well set up system can tend to break out in resonance if you run it at just the right (wrong?) speed for any length of time, with little to no load. Just another thought.

[JerryBurks]

I'm a bit stumped why your resonance issues are so bad and at such a low speed?..............

I don't know either but then, this is my first project using steppers and all I know is from here and other internet places. First I thought this was just related to my funny torque test rig setup and it would go away on a real machine with friction and mass to move. But alas, it did not. Admittedly this is just one evening experimentation and only on the Y-axis but I could get it to stall reliably around 110-120 ipm (about 3 revs or 1200 half steps per second). I strapped the spare wheel of a car with approx. 30 pounds to the Y-sled and it did not make a discernible difference.

When accelerating very slowly I can see that the stall happens around 110 ipm. I tried accelerating faster up to 100 inch per sec^2 and it just makes it stall faster and I don't know exactly at which speed but the motor never gets through this range.

I am pretty sure I will get this under control. I might try a harmonic balancer or other viscous damper, rattler or whatever the recipes are. But for now I will just get one of the praised Gecko drives and hope it solves the problem without such band-aids. I did spend a while on the phone with Mariss @ Gecko and he was very convinced it will. Let's see.....

[ger21]

You're not trying to run those huge motors from a G250, are you?

[JerryBurks]

You're not trying to run those huge motors from a G250, are you?

I was tempted
According to the motor and PS specs it should work fine but I convinced myself to cough up the money for the G203V drives. Besides better spec margins and future option to use higher DC voltage I really like the drive inputs to be optically isolated.

Getting a bit expensive but actually it does not cost me anything because otherwise I probably would have spent the money on my car hobby

[CarveOne]

I'm using a 72vdc 20 amp linear PSU from Keling with my four G203V drives. It's overkill in the current capacity but runs cool and has plenty of reserve capacity for a 5th motor. Do the math to insure that your motors are ok with the higher voltage if you do this also.

CarveOne

[PaulRowntree]

Getting a bit expensive but actually it does not cost me anything because otherwise I probably would have spent the money on my car hobby

I REALLY like your thinking here! So if I get more and more expensive hobbies, they really don't cost me anything. In fact, if they were expensive enough, I might even start making a profit on them! I have to explain this to my wife now, before I forget ...

[JerryBurks]

I REALLY like your thinking here! So if I get more and more expensive hobbies, they really don't cost me anything. In fact, if they were expensive enough, I might even start making a profit on them! I have to explain this to my wife now, before I forget ...

Well, I have to burst your bubble here. Unfortunately you have to start with really expensive hobbies and move on the somewhat less expensive hobbies to make a profit .

I know I should have started with an 80ft yacht, breeding horses or driving Lamborghinis but somehow I missed this opportunity.

[JerryBurks]

X-axis is now also moving under own power

I received the Gecko drives and they make indeed a difference.

I tried first with my old CNC machine on the NEMA23 270in-oz steppers that I never got beyond 180 ipm (not cutting) and they do move with the Geckos up to 700 ipm before they stall.

Now, trying with my new NEMA34 steppers it is also a major improvement. But these motors still seem to be much more prone to stalling and needed experimentation with the acceleration settings. On the x-axis (only one of two motors running) I get up to 500 ipm with acceleration of 30 in/sec^2. That is surely more than I ever need and I am not sure if the stalling that happens then is resonance or if the motors just run out of steam at the given acceleration and friction. After all the power supply is only 48V while these big motors should have 140V (not that the drive could handle that). It would be nice if there was a stepper drive that could use rectified 120V directly, eliminating all the power supply or transformer crap.

Anyway, I think I am satisfied with that result and will just keep assembling.

Oh.....anybody needs 4 nice Chinese stepper drives (80V - 5.6/7.8 amps) this one? Just send me a PM with an offer!

[RomanLini]

Good to see it coming along!

500 IPM is probably way more than you would use anyway, in most cutting jobs the total time is a lot more dependent on actual toolpaths and cutting speed than it depends on the speed of the rapids. I usually run my rapids at about 50% to 60% of their max (to reduce wear and increase reliability) and it makes little difference in total job time on most jobs.

[JerryBurks]

Good to see it coming along!

500 IPM is probably way more than you would use anyway, in most cutting jobs the total time is a lot more dependent on actual toolpaths and cutting speed than it depends on the speed of the rapids. I usually run my rapids at about 50% to 60% of their max (to reduce wear and increase reliability) and it makes little difference in total job time on most jobs.

Makes sense...I just wanted to make sure the motors are not hampered by unnecessary hardware limitations.

But, coming along quite well indeed and the main parts are pretty much done. It is about time to get this thing finished. Maybe another 3-4 weekends with all the small stuff: wiring, limit switches, control box, dust shielding and dust extraction. I am getting a bit antsy about using this machine and I want to avoid having my wife call a shrink for my obsessive behavior.

Latest progress: I machined two 8mm HTD timing belt pulleys for the synchronizing belt of the two x-axis steppers. I had originally planned for aluminum pulleys but since the whole machine is bamboo and this stuff is very hard I made them also of bamboo. Not sure how long they may last but who knows....



More work on the Y-axis, too:

[RomanLini]

Haha! Comeon now you're going too far!
Bamboo pulleys! What's next, bamboo leadscrews? Bamboo linear rails?

Ahh just kidding. If you soak enough varnish into that bamboo pulley it will probably be as good wearing on the splines as most plastic ones. I'm not sure how the interface to the shaft will hold up as that's where all the torque forces will be highest.

[JerryBurks]

Haha! Comeon now you're going too far!
Bamboo pulleys! What's next, bamboo leadscrews? Bamboo linear rails? ........

Well, why not....wooden lead screws have been used for centuries and you can even buy one on the Internet for $150
Now that would be a Green Machine....

[JerryBurks]

Anyway, I am not going that far and stay with metal for critical parts. We'll see if wooden timing pulleys are good enough. In normal operation they do not see any torque after all. There is a a 1/4" set screw in a dowel nut captured by the two pulley half-shells. But I need to take them off again and give the flanges some taper on the lathe to prevent the belts from riding up.

Here a short clip of my machines' first 3-axis movements (use full screen 720p):

[ame=http://www.youtube.com/watch?v=x_2eLPBM7lU]BigBambooCNC.avi - YouTube[/ame]

Z- axis is now also complete.

[PaulRowntree]

I have to admit that the grain (?) of the wood gives your machine a certain style that is hard to match with mdf. I like the pulleys!
Bravo!

[JerryBurks]

I have to admit that the grain (?) of the wood gives your machine a certain style that is hard to match with mdf. I like the pulleys!
Bravo!

Thanks! Now I only need to get it to work as a real machine.

I considered MDF when I designed the frame but for a machine of this size it is just a bit weak. See comparison (from MakeItFrom.com). But admittedly Baltic Birch is almost as rigid as the Bamboo.

[JerryBurks]

I put the various parts on the scale today and ...holy moly... it adds up.

The entire machine is now about 584 pounds

- cart - 70 lbs
- table with x-motors and 80/20 tabletop extrusions - 334 lbs
- complete gantry - 180 lbs, out of that is
- Y-axis moving parts - 67 lbs, out of that is
- Z-axis moving parts 32 lbs

Oh well, I like it sturdy

[RomanLini]

I put the various parts on the scale today and ...holy moly... it adds up.

The entire machine is now about 584 pounds

That reminds me of that quote from the original "Jurassic Park" movie; the kid is playing with the nightvision goggles and the lawyer says "What's that you got? Is it heavy? Then it must be EXPENSIVE! Put it down..."

[JerryBurks]

That reminds me of that quote from the original "Jurassic Park" movie; the kid is playing with the nightvision goggles and the lawyer says "What's that you got? Is it heavy? Then it must be EXPENSIVE! Put it down..."

Interesting way of looking at it. My new machine is then about $6.90 per pound. Maybe I should have made it from steel

But WAY cheaper by the pound than rib eye steak or the SharkPro+ tabletop CNC that I have been using.