Clearpath servo size recommendations for G0704

[wolfmentality]

Hello all! This is my first post, but I have spent a lot of time reading these forums and trying to force some knowledge through my thick skull. I have recently acquired a G0704 and am planning a CNC conversion for it. I would like power it with Clearpath servos via a 2:1 belt reduction and am looking for recommendations on which size to buy. Based on the other builds I have found on this forum, I have narrowed the likely choices down to one of the following:

828 oz-in Peak , 166 oz-in. Continuous
https://www.teknic.com/model-info/CP...del_voltage=75

620 oz-in Peak, 124 oz-in Continuous
https://www.teknic.com/model-info/CP...del_voltage=75

492 oz-in Peak, 98 oz-in Continuous
https://www.teknic.com/model-info/CPM-SDSK-2321S-RLN/

From what I have seen looking around these forums and other places on the internet, the 828 oz-in motor is likely ok for direct drive, but the other two probably need the belt reduction. I like the idea of the belt reduction for two reasons: increased encoder count (1600 counts/rev vs 800), and increased continuous torque. I gather that most conversions have plenty of power to push the table at cutting speeds even with cutting forces and that it is acceleration of the axis over small distances that is the driving force behind motor sizing. If anyone has some experience with these, or other servos that would do well in this application, please let me know what you think. My target upper end for rapids and cutting speeds is about 150 - 200 IPM. I don't see a need to go beyond that, but would love to be able to accelerate the table very quickly.

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[ninefinger]

Its been a long time since I built my machine but with servos of ~50 oz-in continuous and 350 oz-in peak and 4:1 reduction the X and Y move plenty fast enough (100IPM) and the accelerations are enough to jump the machine around. I can go faster but at the time my old control system wouldn't let me with the way I had it configured.(problem with a high encoder count and reduction...). I can go faster now but still don't - you run out of space plenty fast on Y at 100IPM.
My machine BTW is a 12Z (the bigger RF-45 type) so my bet is that the smaller of the servos you showed would be fine.

Other consideration is operating voltage. From the looks of it the higher the voltage the higher the peak torque but the continuous torque remains constant, but the max speed drops too. If I were to do it again I'd go for a 48VDC system as my 75VDC is a bit scary with the amperage and voltage available - it can bite pretty hard. At 48VDC you're still up there in voltage but its a just bit safer - especially with cables running in and around coolant...

Mike

[wolfmentality]

Hey Ninefinger, thanks for replying. I appreciate the advice. How much does your table weigh, and how long does it take you to reach peak speed?

[ninefinger]

I'll see if I can check on the weekend for the answers. For the table I'll have to use the CAD model to get an estimate.

[dazp1976]

I'd go 828oz regardless of reductions or not.
I'd rather have power in reserve than end up on the borderline.

[arizonavideo]

The Clear Paths are not like normal servos. They have high low speed torque and somewhat poor high speed power, much like a stepper.

This is good power to direct drive a 5 TPI ball screw. I generally don't like to tell people what to use if I have not used the part but I have done a fair amount of work with the smaller PM-25 size mills.

The 492 oz should be fine for the X and Y and the 620 will work fine for the Z.

Many people have done 425 oz steppers with the PM-25 mill and been just fine. As you know that means they can never use more then 425 oz or they will loose steps. All steppers loos power as the RPM goes up so at rapid speed of lets say 130 IPM the some what high inductance 425 oz stepper will be making about 150 oz.

Having 4 times that much power should be enough.

[shooter123456]

I just mounted CPM-SDSK-2321S-RLS steppers on my PM25 on the X and Y. Powering them with a 48V power supply, it is managing just under 400 IPM before it starts to give me warnings. Both are direct driven with 1605 ball screws.

The Z has a CPM-SDSK-3421P-RLN motor also powered with 48V. I haven't finished tuning that one yet, but I anticipate a little under 300 IPM on the Z axis.

If I decide to upgrade to the 75V power supply, I anticipate 600 IPM rapids on the X and Y and at least 400 in the Z. That seems like overkill though, so at this point I don't think I will bother.

Also, I tuned the X and Y with 3 4" vises on the table (at least 80 lbs on the 55 lb table). I bet they could manage a little faster if I only had 1 vise mounted.

[wolfmentality]

Thanks for all the insight! Seems like the smaller motors are definitely strong enough then. Shooter, what size do you have mounted on your Z axis?

[shooter123456]

They are plenty strong. I think people have a tendency to shoot for stronger stuff to compensate for poor adjustment or poor quality on other areas. It helps add a little reliability though in some cases.

On the Z, it is a Nema 34 CPM-SDSK-3421P-RLN motor. Peak torque is 547 oz in at 48 volts and top speed is 1910. I used a calculator Teknic recommended and even that motor is over rated for this machine.

[wolfmentality]

I like your choices; those sizes save me a few dollars over the ones I was looking at. What controller are you using? I was looking at using KFLOP, but am still undecided on that. I am going to start making mounts this weekend, so I have a little more time to make these decisions before it is time to purchase motors and electronics.

[shooter123456]

I am using LinuxCNC with a parallel port break out board. It works well for the time being (and for the last 2 years), but I may need something better to support the rest of the things I have added. I am out of IO now with the servos on X, Y, and Z, spindle control, and mist relay. No room to control ATC, any sensors, coolant pump, etc.

[hackish]

I spent a lot of time playing with a clearpath motor and considering dumping my $3k of panasonic units in exchange. When I started to compare the differences between a DMM and a clearpath, the advantages of the clearpath product wasn't that clear anymore. I suspect the downside of integrating the servo amp into the motor is heat. For whatever reason, when they go fast, the torque seems to drop off a lot more than my panasonic units. I haven't gotten around to ordering a DMM one to compare.