Upgrading Taig CNC with Geckodrive G540 to Closed Loop Steppers

Hey everybody,

Long time lurker, first time poster. I'm a product designer by trade and I'm very new to this stuff, so I appreciate your patience and assistance.

I recently bought a Taig CNC from the vendor Deepgroove1, they include a Geckodrive G540 enclosed with a 48V 350W power supply to go along with their Nema 23 2NM steppers. You can see the basic idea here:

https://www.deepgroove1.com/cnc-controller

I've managed to get this up and running with Mach3 on a computer running XP, and have been putting the machine through it's paces. I'm going to be making small injection molds out of aluminum, so I ran some very small bits and did some highly precise finishing passes. The mill is performing great, but a few times the steppers have bound up and knocked everything out of whack when doing long, detailed work. I've oiled the machine and did my best to get it dialed in, but it still seems to happen sometimes. Fortunately I was able to hit the e-stop button quickly enough to save the parts, but this has me considering closed loop hybrid steppers like the ones from stepper online. That way if the steppers bind I can at least have it trip the e-stop so I don't have to babysit it quite so much.

My question is how do I go about upgrading my current system? I was looking at the following closed loop stepper system:

https://www.omc-stepperonline.com/cl...-2m-cable.html

How do I go about making this work together? It looks like the closed loop steppers each use an individual power supply with their controller. My assumption is that I need 3 power supplies, and run the gecko off one of the axes? Then I wire the signal output from the gecko to the individual closed loop drivers and wire the alarm from each driver into the emergency stop? Sorry if this seems obvious, I did some searching but still want to make sure I'm heading in the right direction.

Thanks!

- Jon

Stepper to G540 to a pc running Mach3 doesn’t have a way to add a feedback signal. It’s open loop. Closed loop steppers have an encoder which feeds back to the driver and sometimes a dedicated motion board(not using Mach).

You either need more power (assuming the steppers are stalling) or need to lower the cutting loads. Btw G540 on a large nema 23 stepper generates a decent amount of torque. I use this combination but my steppers are 4” long. You can only put so much power into that size machine

Since you already have the drive system, I would try to lower the cutting forces: Different cutter, higher spindle speeds and or less stock. Are you sure the spindle didn’t stall? Cutter load up with aluminum?


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My binding issue happened once when I was cutting with 1/32" bits at 10,000 RPM and removing 0.005" per pass (the bits are really delicate), so I don't think it's an issue with cutting force. I brushed a good coat of oil on the leadscrews and I'll run some more paths to see if I can replicate the issue.

Another thing I came across was the Step-Lock by Larken:

Step Lock, ViperServo

Looks like it might do what I need, and would work with my machine because I have double shaft steppers. I would have to source the encoders myself which is a bit of a can of worms. Thanks for your input!

Hi,
I'm not a fan of closed loop steppers.

They have an encoder which closes the loop back at the stepper driver. If the stepper misses a step the encoder detects it and the drive inserts extra steps
to catch up. Its not a case of putting an encoder on an existing stepper, you need a drive that can insert the extra steps. The only way to have closed loop
steppers is to have matching stepper/encoder and smart drive.

The problem is that if a stepper, any stepper, loses a step, then it is marginally overloaded at its current velocity. Thus any extra inserted step will also likely get missed.
The real problem is that your stepper is marginally overloaded, and cutting forces are not the culprit but it suffering from lack of torque at the speed its operating.
ALL steppers lose torque the faster they go. Its not uncommon for a stepper to have as little as 5% of its holding torque at 1000rpm.

Closed loop steppers suffer from degrading torque at speed exactly as open loop steppers.

The manufacturers of closed loop steppers will tell you 'you'll never miss a step' .....pure BS, they do that to capture sales. Closed loop steppers do have two advantages:
1) They will alarm out and stop if too many steps are lost rather than proceeding with the job and wrecking it
2) They can use interpolation to achieve higher resolution than can be achieved with open loop steppers

Neither of these advantages are enough to justify the premium you will pay.

I would suggest you look critically at the steppers you have already, you may be able to swap them out for LOW inductance steppers and that may in itself solve the
problem.

If not the get AC servos, they will EAT ANY STEPPER EVER MADE, but a a cost.

Craig

Hi Jon - Does the G540 have limiting resistors in place? The first system I set up with G540 kept cutting out with peak loads. Turned out it was because of no limiting resistors in place. Since using these no problems... I would keep working on getting a good understanding of the issues you have before upgrading anything. Upgrading may not solve your problem if it is incorrectly diagnosed...Talk to the Gecko people they have been very helpful on my first machine...

If its a "binding" issue & occurs with no tool load then its a machine mechanical issue. You need to check all drive systems are correct before you proceed to any upgrades. Peter

Interesting about the step lock board. Not sure but it looks like it’s $80 per channel. Plus $35 for each encoder. Looks like it keeps tract of steps in and sends a error signal if step doesn’t match encoder rotation. It would do the job and protect the part and cutter. I think you could do that with a micro like arduino, if you know how to code.

Not possible to stall a stepper on a G540 with a 1/32 dia cutter. Having to lubricate lead screws, to not stall, is unusual. Looked at those machines once but thought they were too small to cut metal.

Good valid points on the above post. Servo is the solution but way overkill for that machine


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Quote:

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Originally Posted by peteeng

Hi Jon - Does the G540 have limiting resistors in place? The first system I set up with G540 kept cutting out with peak loads. Turned out it was because of no limiting resistors in place. Since using these no problems... I would keep working on getting a good understanding of the issues you have before upgrading anything. Upgrading may not solve your problem if it is incorrectly diagnosed...Talk to the Gecko people they have been very helpful on my first machine...

If its a "binding" issue & occurs with no tool load then its a machine mechanical issue. You need to check all drive systems are correct before you proceed to any upgrades. Peter

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Interesting, I'll have to check this out. I didn't put together the control box so I'll crack it open and see if there are resistors in place.

Thanks for all your help everybody, I'm going to focus on tracking down any issues with my current steppers and I'll keep you updated.

The other thing that might cause this is overheating; when you've got it open you can check to see if there's adequate cooling and heat-sinking.

I opened up the control box to take a peek inside. Pretty empty in there. The extra outlet isn't wired and it looks like there's a spot for a fuse holder that's been plugged. No additional heatsinking or cooling. I cracked open the Z axis connector and found a limiting resistor in place, looks like 2.49K but I'm bad at reading these things.

Anything else I should keep an eye out for?

It might help, then, if you mounted the G-540 on a finned aluminum heat-sink and put a fan in there to blow air past it. Maybe you can hook it up to that unused AC outlet. Especially since summer's coming...

Hi Jon - If limiting resisters are in place that's good. (check all axis have resistors) I presume you have Rev8 G540 so here's the manual. My gecko machine lived in queensland and it was quite hot all year round and I didn't put additional cooling in place. But any cooling for electronics is a good idea. So now I think you have to check the mechanics of the machine, sounds like somethings sticking, gibs, slides bearings etc

My story with the G540 (preR8) is that Gecko admitted that when 4 drives were used at near 3A the current limiting/cut off function was a bit sensitive so they sent me a note on how to correct that plus use the resistors. After that all good. Rev8 has that mod...I've tried to fry the G540 a couple of times and its bulletproof in my opinion. good luck Peter

Checked all 3 axis and they had resistors. I've noticed that my steppers make a lot of noise at idle, it's like a hum. I figured it was a noisy power supply, they seemed to operate normally. Thought it might be worth mentioning.

Thanks!

Hi Jon - Steppers don't idle. They are on all the time. The hum is normal. The current is flowing into the coils and holding the windings/shaft in place. That's why they get warm... some systems sense if the motor is not moving and will cut the current 50% or 75% (usually can be set via dip switches) but in some applications where you are using the holding torque you don't want the current/torque to be turned down. cheers Peter

Quote:

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Originally Posted by jonpanic

Checked all 3 axis and they had resistors. I've noticed that my steppers make a lot of noise at idle, it's like a hum. I figured it was a noisy power supply, they seemed to operate normally. Thought it might be worth mentioning.

Thanks!

---

Hi,
There is no need to replace the G540 with a closed loop stepper system. You will just be wasting money. The G540 is a perfect match for a Taig. I have two Taig mills running on G540 controllers. The machines never loose steps. I also run a much larger machine of a G540 controller as well. Is a TM20VL, similar to the PM25VL. I can get rapids of 4000mm/min, although I’ve dialed then down to around 1500mm/min.

The axis will be stalling because of;
1. Resonance,
2. Too high acceleration
3. Max velocity is too high
4 Gibs are too tight
5. Gibs are too loose.

My guess is that it is either problem 1 or 2.

It may be that the steppers are stalling due resonance in the stepper motors. This is due to them not being tuned for the G540.
Each of the four axes in the G540 needs to be tuned for the stepper motor connected to it. On the back of the G540 there is a hole for each axis so you can adjust the trim pot accessible by the hole.
To tune the axis drive the motor at a feed rate so the motor is turning about two revs a second or where the stepper motor is at its noisiest. You will know it when you hear it.
Then with the axis at it’s limit of travel issue a G1 command in MDI to move it to the other limit of travel, i.e. G1 X300
Then, while it is moving adjust the trimpot to a position where the noise is at it’s minimum.
Do this for each axis.
Cheers,
Peter


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Here is a video testing the G540 controlling the TM20VL

https://youtu.be/AjfhQUBjBjI

Cheers
Peter


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