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Nema 24 motor occasionally gets stuck

Nema 24 motor occasionally gets stuck

Postby bdg2014 » Sun Jan 11, 2015 8:44 pm

Hey All,

I have been off and on building my blackfoot variation. I'm feeling really good about the y-axis and how it moves but I don't feel as good about the y-axis and haven't really studied the z-axis.

I observe specific areas that the y-axis seems to get stuck in. The motor will try to turn but not be able to and if a give a little push it may get over the tough spot. If I take all the load off, no router, no chains I don't feel significant resistance.

Secondly although I bought the motors from builyourcnc they are nema 24 and my wiring that appears to be working doesn't match any documented wiring on the website. If I follow the documented wiring for the NEMA 24 425 oz motor for bipolar series I get a motor that clicks but makes no forward progress, much like when the y-axis gets stuck above.

My first question is this a wiring problem or a load problem.

My second question is why does my motor wiring seem so different from the current motors. I bought my motors more then 2 years ago.

Ben
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Re: Nema 24 motor occasionally gets stuck

Postby Awesomeness » Mon Jan 12, 2015 3:22 am

425 in*oz motors shouldn't have any problems moving a y-axis of a reasonable weight (let's say 25lb). That probably means something else is going on. Motors can have resonance points - speeds at which they do not operate well - try faster or slower, or more or less acceleration. Also, you may have something binding or dragging - feel free to push the assembled carriage around, with the motors unplugged. You will get inductance resistance, but you should be able to compare the difficulty pushing the y-axis to the x-axis, and get a feel for if there is a sticking point.

As for the wiring, who knows. There is no industry standard for wiring colors on motors, so practically every model has a different color scheme. Just make sure you're using the diagram for your specific model of motors, and wire accordingly. When in doubt, ignore assembly/wiring instructions that tell you to "put the <specific color> wire to A+ on the driver", and verify that the A+ wire on the motor is going to the A+ driver terminal, and so on.
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Re: Nema 24 motor occasionally gets stuck

Postby ShenValleyCNC » Mon Jan 12, 2015 1:53 pm

If the Y-axis moves moves smoothly across the face of the gantry, you likely are not experiencing a binding or load issue. The load should remain constant through the move.

The schematic that came with my motors, also from buildyourcnc, had only colors listed and not A+, A- etc. for the motor wires. But it did provide a wiring diagram for Bipolar, Parallel and Unipoloar. I ended up using the parallel wiring setup as it was the only one I could get to work. Interestingly, I had to swap the wires from A+, A- to B+,B- to make it match the directions in my controller, it would only run backwards. I have a LinuxCNC controller, CW230 drivers and 60BYGH303-13 Nema 23 motors.

Here is a link to the schematic with wiring diagrams. https://www.buildyourcnc.com/Documents/PN.SM60HT86-2008BF-U%20%28inhouse%20PN.60BYGH303-13%29%20%281%29.pdf

From the schematic--8 wire motor parallel wiring
A+ -> Red/Blue
A- -> Yel/Blk
B+ -> Brn/Wht
B- -> Org/Grn

Check all your settings. Redo your calcs, check that wires are firmly connected. Early on, I found that I had one dip switch set wrong. I had carefully set them and was sure they were correct.
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Re: Nema 24 motor occasionally gets stuck

Postby bdg2014 » Mon Jan 12, 2015 2:59 pm

I bet it is the resonance frequency problem. I'm stumbling around and don't know exactly what are reasonable settings for initial velocity, feed rate, acceleration, and jerk limit.

I'm currently using a 100 for my initial starting velocity a federate of 1250 both in steps and an acceleration of 5 steps/s^2

I do the see the behavior in specific area but it could be based on time of travel. Starting fresh in a trouble spot I think works correctly. I'm going to focus on the frequency and binding problems.
I will assume since the motors are working 98% of the the time the wiring is correct. If so I won't ask for free advice on using a multi-meter to identify the motor leads. I tested across each lead and identified that 4 had no continuity and 4 had resistance of around 3 ohms(?).

I have gotten pretty far but I barely know what I'm doing so any guidance is appreciated.

Thanks,

Ben
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Re: Nema 24 motor occasionally gets stuck

Postby ShenValleyCNC » Tue Jan 13, 2015 5:08 am

I rarely run at 100 ipm. Most of my cutting is usually in the area of 60ipm. Try slowing it down and see if the problem is apparent.

While the specs say the motors can do different levels of microstepping, this may not be the case in practice. Our equipment may not allow it, so you have to try different settings and see what works.

I found a great article online to help me with my stepper config. It shows how to calculate what your system is capable of, and then the calculation of steps per inch in relation to the driveline ratios. http://www.britishideas.com/2008/04/29/configuring-emc2-for-three-axis-stepper-motor-control/
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Re: Nema 24 motor occasionally gets stuck

Postby bdg2014 » Tue Jan 13, 2015 10:06 am

Cool I hadn't seen that page I will go over it and see if anythings turns up. I won't get to it until at least friday.

Thanks,
Ben
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Re: Nema 24 motor occasionally gets stuck

Postby krugshouse » Wed Jan 14, 2015 1:45 pm

For what its worth I had a simular problem with my X axis (425 oz) stalling at random times. not sure what was the true problem but when I set my motor tune to 250 accel and 4 velocity, then using 60 to 100 IPM feeds, my problem stopped. I had been running 700 and 5 on my motor tune, which seemed to be to high for my Blackfoot. Not that this will help you, but with the Blackfoot 4.2 ver, I think the 425 oz motor, although it works it is underpowered. I will upgrade to the 650oz and new driver once the 425 oz dies. But with the smooth and constant way its running now I dont think it will die anytime soon.
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Re: Nema 24 motor occasionally gets stuck

Postby Awesomeness » Thu Jan 15, 2015 9:08 pm

krugshouse wrote:... when I set my motor tune to 250 accel and 4 velocity...


For clarity, he means 4 acceleration and 250 velocity. He had them switched. Don't try to set to 250 accel.
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Re: Nema 24 motor occasionally gets stuck

Postby bdg2014 » Mon Jan 26, 2015 10:14 pm

Not resolved but I wanted to update my post.

I have looked into the modifying my move settings and I have seen an improvement. I also happened to notice the that x-y axis rails are being worn down in a weird way. They were getting a flattened edge and I noticed an accumulation of aluminum in the problem area. I have now removed the gantry and I will be reassembling the whole shebang and see what is what. Thanks for your help and advice.
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Re: Nema 24 motor occasionally gets stuck

Postby airnocker » Mon Feb 23, 2015 3:17 am

You will get inductance resistance, but...


I think Awesomeness means to say "inductive reactance" can act as a resistance to current flow. Electrical "reactance" is a resistance or an opposition to current flow in an electrical circuit or component that has inductive or capacitive electrical qualities at certain frequencies. A stepper motor is primarily an "inductive load" to the driver.

You should expect some "flattening" of the aluminum angle corners that the v-groove bearings are rolling against but it should not result in a constant wearing resulting in lots of aluminum filings. The opposing aluminum angle for each axis should be extremely parallel to each other throughout their entire length, otherwise spots where the opposing v-groove bearings are rolling that are wider than other areas will create pinching.
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