Dual y axis motor problems

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danimal
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Dual y axis motor problems

Post by danimal » Sat Sep 21, 2013 2:55 pm

So I have run the dual y axis conversion since the day that I got the machine. I used to have it set up with 1000 mm y axis and 375 mm dual x axis. Just recently I made mount plates and swapped to a 1000 mm dual x axis and a 375 mm Y axis which I am going to scale up to 500 mm here soon. I knew that there were going to be some issues stabilizing the whole thing again and I have gone through all of the build logs and have a good idea where I am going with the build to do that. But in the mean time I am wiring in limit switches and other various upgrades to make operation a little more reliable.

Now here is where the problem starts. I have dual y motors hooked up to the same driver on the GRBL shield. I have never liked this on principal, but it was something that I had to do until I could figure out a better solution and it seemed in my previous configuration to contribute greatly to accuracy. But now it seems that only one motor actually works and the other one just barely tags along with little or no torque. When the motors are supposed to be holding, the most distant one with the longest cord works just as it is supposed to, but the close one with the shorter reach is movable just like it is disconnected. I pulled the wires and separated them and did an operational test on each motor individually, and they both work perfectly. The way I have my machine set up I have a single wire coming from the driver, then I split at the first and closest motor to daisy chain to the other motor in parallel. I doubt that this would have a negative effect over running two separate wires into my enclosure to the driver, but that is the only difference in the way the two systems were configured.

I knew that wiring the two motors meant that they would share the real load capabilities of the driver and thereby would be running at a lower torque and performance level, but I thought that it should be closer to 50/50. That appears not to be the case and it is strange to me. Has anyone else observed this?

So now I am moving on to my solution, and that is to run a forth driver and split the control signal. I think that this is the best idea for setups with a long x axis split anyway. I have been shopping around for a cheap but reliable driver and I wanted to see what you guys knew of. There are several out there, but the reviews on them are hit or miss. I think that I am going to go with the spark fun driver, because I could drive down and pick it up today, but if there was a better option out there then I am not in such a big hurry that I cant wait for it to be shipped. Let me know what you recommend. Thanks
Shapeoko # 1458

RT0701C Spindle || dual y motor || x axis nema23 with custom carriage 1000mm length || z axis nema23 linear rail upgrade with 1/2-10 ACME

bjbsquared
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Re: Dual y axis motor problems

Post by bjbsquared » Sat Sep 21, 2013 8:19 pm

I am running dual Y motors with one driver and have not had this issue. As far as I can tell I have equal power to both motors. my machine is in a 1Mx1M configuration with 2 x rails.

Have you phase one motor opposite the other so they turn in the same direction?

Have you adusted the driver current limit?
#1016 - 1M x 1M Y: Dual Motor Drive w/Looped Belts, X:Dual Rail with wlanfox blocks, Z: Stock, Spindle:DW660

twforeman
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Re: Dual y axis motor problems

Post by twforeman » Sat Sep 21, 2013 10:03 pm

danimal wrote:The way I have my machine set up I have a single wire coming from the driver, then I split at the first and closest motor to daisy chain to the other motor in parallel. I doubt that this would have a negative effect over running two separate wires into my enclosure to the driver, but that is the only difference in the way the two systems were configured.
This is exactly the way I have my machine wired. What gauge wire are you using? I just got done rewiring my machine with 22 AWG wire and it runs great.

I would make sure that all your connections are good and tight. Also check the driver current adjustment.
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Gadgetman!
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Re: Dual y axis motor problems

Post by Gadgetman! » Sun Sep 22, 2013 9:35 am

When running two motors in parallell, it's a good idea to make certain that the wires to the motors are of the same length/thickness. That way they have the same resistance and the current flows equally to both motors.
And replacing them with thicker wires is also a good idea.
Weird guy...
Shapeoko 2014F: 1000mm X/Y, 300W Quiet Cut spindle, Arduino Uno/G-shield and GRBL 0.9i
15x30 drag chains, custom spindle mount, 9mm belts, 8mm endplates, 6mm motor plates.

danimal
Posts: 332
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Location: Colorado

Re: Dual y axis motor problems

Post by danimal » Sun Sep 22, 2013 7:03 pm

bjbsquared wrote:I am running dual Y motors with one driver and have not had this issue. As far as I can tell I have equal power to both motors. my machine is in a 1Mx1M configuration with 2 x rails.

Have you phase one motor opposite the other so they turn in the same direction?

Have you adusted the driver current limit?
Motor direction of rotation has been verified, as well as independent checks on each motor operation. I also checked the coil resistances and found both motors to be exactly the same from the split. It is actually the motor with the additional cable length (far side motor) that runs while the one that is directly connected to the incoming main wire that is gutless. I have adjusted the driver up until it stops functioning reliably due to over heating (which is pretty high for my system because I have a high CFM fan blowing directly across both boards) I dont think that I had this problem before, and I can see that the motor is trying to do what it is supposed to, but it just has no power.
Shapeoko # 1458

RT0701C Spindle || dual y motor || x axis nema23 with custom carriage 1000mm length || z axis nema23 linear rail upgrade with 1/2-10 ACME

danimal
Posts: 332
Joined: Wed Mar 13, 2013 5:53 pm
Location: Colorado

Re: Dual y axis motor problems

Post by danimal » Sun Sep 22, 2013 7:08 pm

twforeman wrote:
danimal wrote:The way I have my machine set up I have a single wire coming from the driver, then I split at the first and closest motor to daisy chain to the other motor in parallel. I doubt that this would have a negative effect over running two separate wires into my enclosure to the driver, but that is the only difference in the way the two systems were configured.
This is exactly the way I have my machine wired. What gauge wire are you using? I just got done rewiring my machine with 22 AWG wire and it runs great.

I would make sure that all your connections are good and tight. Also check the driver current adjustment.
I just rewired mine with 18 gauge. I was thinking of upgrading to NEMA 23 and getting new drivers so I went up in gauge, but that should not have any negative affect that I can think of. I checked all connections and went as far as to solder the non working motor directly to the incoming main wire. Then I connected the remote motor across the terminal block. Same result.

I think that I am going to pull the motor and swap it with a new one to see if by chance there just is something wrong with it. Unfortunately I have soldered and heat shrinked all of the motor connections for my other motors so it will just be easier to get a new motor and swap it in.
Shapeoko # 1458

RT0701C Spindle || dual y motor || x axis nema23 with custom carriage 1000mm length || z axis nema23 linear rail upgrade with 1/2-10 ACME

danimal
Posts: 332
Joined: Wed Mar 13, 2013 5:53 pm
Location: Colorado

Re: Dual y axis motor problems

Post by danimal » Fri Sep 27, 2013 7:29 pm

So a quick update. I found out that the pulley on one of the y motors was loose. :( And I found this out about 5 seconds before I was going live with the 4 stepper driver. I figured what the hell, it is already installed, I might as well use it. That is when the fun started, I not only released the magic smoke but a fireball of incredible fury shot out an lit some of my design papers on fire. I still have no idea why this happened, other than maybe there was an arc or something where I soldered in the driver mount. It was a little tight building the solder bridges for the terminal connections, but everything resistance checked out. Here is what I did for the connection, straight from the spark fun website. The only things that i did differently, were 24V (it is supposed to be rated for 30V, 750mA) and I ran the DIR and STEP pins to pin 6 and pin 3 respectively on the arduino.

Image

Do you see anything that I did wrong? I checked and rechecked polarities and everything is exactly in this configuration, and that is what I thought was the correct configuration. I am ordering another A3967SLBT to solder in there and give it another go if I can find out where I went wrong. Thanks for the help in advance.
Shapeoko # 1458

RT0701C Spindle || dual y motor || x axis nema23 with custom carriage 1000mm length || z axis nema23 linear rail upgrade with 1/2-10 ACME

cvoinescu
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Re: Dual y axis motor problems

Post by cvoinescu » Fri Sep 27, 2013 7:50 pm

Is that a separate power supply for the additional driver?

If it's the same supply, is it possible that you wired it backwards?

Can you tell where the fireball originated -- what blew up?
Proud owner of ShapeOko #709, eShapeOko #0, and of store.amberspyglass.co.uk

Gadgetman!
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Re: Dual y axis motor problems

Post by Gadgetman! » Fri Sep 27, 2013 7:58 pm

It's generally NOT a good idea to use two separate PSUs.

If they're of the cheaper sort without proper separation between the AC and DC side, you may find that you suddenly have 110 / 230V difference between the GNDs... Not fun...
And no, a transformer may not always separate the AC and DC sections properly.
Weird guy...
Shapeoko 2014F: 1000mm X/Y, 300W Quiet Cut spindle, Arduino Uno/G-shield and GRBL 0.9i
15x30 drag chains, custom spindle mount, 9mm belts, 8mm endplates, 6mm motor plates.

cvoinescu
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Re: Dual y axis motor problems

Post by cvoinescu » Fri Sep 27, 2013 10:20 pm

Well, it should, and there are codes and laws that try to ensure that the separation is maintained during operation, even when things go wrong. To give only a few examples:
  • A capacitor connecting line to ground (used in, for instance, EMI filters), whose failure can lead to danger of electric shock, must have a special safety rating (Y2). If the capacitor fails, it must fail in a way that does not endanger the user (e.g., not shorted). For line-to-line capacitors, a less stringent standard (X2) is required. Those are only expected not to catch fire when they fail.
  • There must be empty space on a PCB between components energized at mains voltages and the low-voltage section that can be touched by the user (called creepage distance). How wide this is depends on whether the PCB is coated (e.g. solder resist mask) or not. If bare, the minimum prescribed distance is larger than the distance between the opposite sides of a standard 0.3" DIP package, so now you know why many optocouplers also come in 0.4" wide DIP packages (which are identical, except the leads are bent differently to achieve the wider spacing).
  • Parts and wires that may move and make dangerous connections must not rely on solder alone to keep them in place. This is why you see off-white hardened goop that looks like it's been dripped over the parts in many power supplies.
  • Transformers must have double insulation between the windings.
Now, if you've ever opened a few cheap, unbranded power supplies made in China, you've probably noticed that some ignore all of these points, sometimes for foolishly small savings (such as a marginally smaller PCB). Stay away from such supplies, or understand the risks. Simply being made in China does not mean a power supply is unsafe: if it's been made for a reputable brand, it's most likely built correctly and meets safety regulations worldwide.

Unfortunately, some reputable businesses get conned into importing non-compliant, potentially unsafe supplies, and sell them on, not even realizing they're doing something wrong (and illegal). Simply having bought a supply from a local store or from a company in a country with good safety standards does not guarantee that it meets safety regulations. For example, this power supply, sold by a British company, has a plug that's not compliant to BS1363, and thus illegal to sell. You need to take just one glance at the image to tell that the distance between the pins and the edge of the plastic surface they protrude from is much less than 9.5 mm, the minimum required. I bet they have no idea (I've emailed them). Care to bet your life on whether the inside is built with any more consideration for safety regulations? (I haven't opened mine yet, and I'm not qualified to tell, although I can spot the more egregious violations.)

[Edit] I found and opened the supply above. It is better than expected, with a proper regulator IC (SD4843P67K65, if anyone cares), sizeable isolation distances, some double insulation, and some regulatory markings on a safety-critical capacitor (can't read them all without desoldering it, so I don't know if it's the required Y rating in that position), but I think it fails the "solder alone is not enough" rule, although there has been some effort in that direction too. The label is grossly incorrect, showing the square-in-a-square symbol for a class II apparatus, when the earth pin is actually connected to the USB ground and connector shroud, making this a class I device. I'm pretty sure the German GS logo does not represent any actual approval, and is illegible anyway. The country of manufacture is not shown anywhere (it's required by law, even in cases like this when it's not hard to guess). I feel much better about using it, though, now that I've looked inside.
Proud owner of ShapeOko #709, eShapeOko #0, and of store.amberspyglass.co.uk

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