Can two clearpath servos be used to power one axis?

[MtrMeng2001]

What is DMM? Are they good?

[ger21]

dmm-tech.com

[ericclinedinst]

Think I'm taking this advice. Gerry, are you currently using these?

I spoke to the people at DMM they seem pretty willing to work with people and customer support seems on point so far.

dmm-tech.com

[ger21]

No, but I plan on it. The only thing you can get cheaper are unbranded chinese drives, and even those aren't that much cheaper.
I just need to save up $1500

[1Jumper10]

I am planning a build of a 6x4 router build, and am considering the use of clearpath servos. Has anyone else used these where TWO are required to drive both sides of the gantry to move X?

I really like them, and am pretty set on using them, but the design I want to use needs two motors, and I understand this can be a problem for the clearpath servos, both in set up and perhaps in running as they dont stall out due to having high torque, so if things got of square could it lead to more serious problems?

I built a 6ft by 4ft router using ClearPath CPM-SDSK-3421S-ELN for X and Y axis'. My thread is here: http://www.cnczone.com/forums/cnc-wo...10480-cnc.html

There was an issue auto tuning the motors on the Y-axis as it is a dual driven gantry. I had to use the motor tuning file for the X axis just as Teknic Tom described earlier in this thread for the Y axis motors. I'm building another router for myself right now and it will also use ClearPath SDSK servo's.

I built my own cables and saved a lot of money versus buying the factory cables. It wasnt hard at all and Teknics user manual has detailed connector instructions that removed any guesswork.

Ref the IPC 500 power supply: My friends machine used double stack NEMA 34 motors and a NEMA 23 on the Z axis. I havent had any issues with the power supply. A couple days ago I was using my friends machine continously for about an hour. I was using a 1/4" cutter taking a .3" depth of cut and cutting at ~400 IPM. The X axis was doing most of the moving and since this is still a relatively new machine I was curious how the servo's were handling the load. So I kept feeling the X axis motor to see if it was getting warm at all. Even after an hour cutting at 400 IPM it was not even warm. Cool to the touch. If the status LED wasnt lit and it wasnt moving I wouldnt have any way of knowing it was even powered up. I really feel like I could have used NEMA 23 motors on the machine and been perfectly fine.

[RakmUp]

I am thinking about adding these Clearpath servo's to my system but my gantry Y has quite different drive ratio than my X-axis as it was all pieced together from what was available on e-bay for the sizes I needed. Can they still be slaved to drive my gantry Y?
Otherwise I may still gain something by using them strictly on my X, Z and (4th) A axis.

[TeknicTom]

Hi RakmUp,

Thank you for considering the ClearPath integrated servos. The most important aspect when using the auto-tuner for a single motor to create a file for a dual motor gantry is to simulate the reflected inertia properly. If the mechanics are the same between the two axes then it is a simple matter of adding weight to the single motor axis to simulate what each dual motor will be moving on the gantry. If the mechanical design is different between the two axes, then the appropriate amount of weight should be added to simulate the reflected inertia.

If you are not satisfied with the results, you can contact Teknic directly for more assistance.

[RakmUp]

Hi RakmUp,

Thank you for considering the ClearPath integrated servos. The most important aspect when using the auto-tuner for a single motor to create a file for a dual motor gantry is to simulate the reflected inertia properly. If the mechanics are the same between the two axes then it is a simple matter of adding weight to the single motor axis to simulate what each dual motor will be moving on the gantry. If the mechanical design is different between the two axes, then the appropriate amount of weight should be added to simulate the reflected inertia.

If you are not satisfied with the results, you can contact Teknic directly for more assistance.

Thanks for the reply...Do I understand you right? I take half of the weight of the Gantry and add enough to the X-carriage to weigh one half of the gantry? It would be a lot...(6" Sq Tube steel w/1" round ways) And the Y-B drives are on 5/8" ball screw and the X is on 30mm ball screw of different pitch.
That can work?
I am kind of afraid to run the auto tune program on one side of the gantry as it is a heavy gantry rail...and weight alone could not significantly reproduce the vibrations and potential slop that may occur with your hard stops and starts of autotune. It moves easy by one hand but no telling how much racking may be going on. Is it a problem to run these on some axis but not all?

You can see machine basic design on my profile page. The actual is there too...but not as big.

Thanks!

[1Jumper10]

Don't run auto tune on one motor of a dual motor gantry. Tried it, epic failure. Aside from the difference in mechanical characteristics running just one motor, you would be tuning it to double the weight it would be carrying when under normal operation since the gantry is driven by 2 motors. Each motor carries half the gantry load.




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[TeknicTom]

You run the auto-tuner on your short axis that runs side to side (not on the long dual motor gantry axis). In the example below that I wrote for Hands On CNC I used "Y" as the single motor axis and "X" as the dual motor gantry. For X and Y axes with different pitch screws, you need to calculate the reflected inertia to determine the appropriate amount of weight to add.

1) X and Y axes are often the same mechanical design to make the machine easier to build and to make the command creation (math) easier2) The vertical Z axis is almost always a different mechanical design than the X and Y3) The optimal way to create a dual X file using the auto-tuner is to load 1/2 the total X gantry weight onto the single Y axis and then run the auto-tuner. You usually would not use the Z axis because it is biased downwards based on gravity (which dual X axis is not) and because of the mechanical differences.4) After auto-tuning the Y axis with the additional weight, load the file into both X motors.5) Click the "Reverse Direction" checkbox for one of the X motors and save the two X motor files with different names (e.g. XA_SDSK-3421S_rev1 and XB_SDSK-3421S_rev1)6) Run the machine. If the X axis does not seem to have optimal tuning, trying moving the "Fine Tuning" slider to the left to see if your results are better. You will need to do this with both X motor files before evaluating the effectiveness of this step. If you make any changes, re-save the new files (overwrite the old files or create new names) so you have the files saved in a safe location for the future.

[TeknicTom]

Sorry. Didn't format properly.

1) X and Y axes are often the same mechanical design to make the machine easier to build and to make the command creation (math) easier

2) The vertical Z axis is almost always a different mechanical design than the X and Y

3) The optimal way to create a dual X file using the auto-tuner is to load 1/2 the total X gantry weight onto the single Y axis and then run the auto-tuner. You usually would not use the Z axis because it is biased downwards based on gravity (which dual X axis is not) and because of the mechanical differences.

4) After auto-tuning the Y axis with the additional weight, load the file into both X motors.

5) Click the "Reverse Direction" checkbox for one of the X motors and save the two X motor files with different names (e.g. XA_SDSK-3421S_rev1 and XB_SDSK-3421S_rev1)
6) Run the machine.

If the X axis does not seem to have optimal tuning, trying moving the "Fine Tuning" slider to the left to see if your results are better. You will need to do this with both X motor files before evaluating the effectiveness of this step. If you make any changes, re-save the new files (overwrite the old files or create new names) so you have the files saved in a safe location for the future.

[TeknicTom]

BTW, awesome build 1Jumper10. The quality of your build shows that this is not your first rodeo. You have made an impressive amount of progress in the last week. Nice job

[1Jumper10]

Thanks Tom. I had the week off from my day job so I had to take advantage of that. A couple more weeks and I'll be close to buying the SDSK servo's.

[DDgitfiddle]

Tom,

A quick question for you: I have the gantry off my machine anyway, so I assume it is reasonable to just tune one of the Y-axis motors with half the gantry weight instead of using the X-axis? Seems a little more direct than using the X-axis, but I can understand why people would want to avoid removing the gantry.

Thanks,
Robert

[TeknicTom]

Hi Robert,

the usual process is to have the gantry on the machine with the gantry motors (I usually call them X1 and X2) enabled with the factory default files. You won't be moving the gantry. This is just to hold the gantry position and to make it stiffer for the short cross gantry single motor (I usually call this Y). Many people also tune with X1 and X2 disabled with good results.

You want the machine to be as close to final assembly as possible (this means with the gantry on the machine). This allows the auto-tuner to analyze the harmonics of the machine. The more you change the set-up from the final assembly, the more variables that are introduced into the process. Would your approach work? It might, difficult to say.

Hope that helps.

Tom T

[DDgitfiddle]

Tom,

Thanks for the reply. It will probably be a couple of weeks before I get to the point of tuning the motors, but I think I will give it a try both ways and store the config files. I understand your point about stiffness and harmonics. I am building a FineLine Saturn 2x4, so the main frame is pretty stiff anyway. The question is which is more accurate: simulating one of the X motors using the Y axis drive or tuning without the gantry in place. My gut feeling is that the harmonics might be a second-order effect relative to the weight, but it won't hurt to try it both ways.

Thanks,
Robert

[SammyHicks]

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