[southpaw]

Wondering what Watt size servos people are using for their machines. I'm pretty set on Clearpath servos for compactness, ease of installation and setup.

And I appreciate that their torque curves aren't as good as some other options out there, but wondering what people have successfully used in their own builds. Looking to build a standard gantry setup. Ball screw with twin Y motors.

Any feedback or suggestions appreciated.

Best,

Max

[Richmaple]

Using CPM-SDSK-3411S-ELS with my Avid benchtop pro 2x3, which is at least similar in that it's a ballscrews driven gantry cnc. Tons of power but you'd need a different model depending on what your ballscrew pitch is and how heavy your gantry is, etc.

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[ger21]

Yes, different drive systems or screw pitches, have a major effect on motor choice, so you need to know exactly what components you'll be using. Once you know that, you need to choose a performance goal to match the motors to.

[southpaw]

Yes, different drive systems or screw pitches, have a major effect on motor choice, so you need to know exactly what components you'll be using. Once you know that, you need to choose a performance goal to match the motors to.

Right, of course. Sorry for the lack of detail. I'm using the 4×8 CNC kit from VXB:
https://www.vxb.com/8-X4-Feet-CNC-Router-Kit-16mm-Rail-Guide-System-p/8x4-feet-cnc-linear-guide-kit.htm

Which has 20mm ballscrews on the Y.

For the gantry, I'll probably start off with an openbuilds design and move to something beefier down the road. My biggest concern is the gantry weight because I'd like to put a honkin spindle on it and don't want to underpower it. I don't need crazy rapids or anything, but I want the machine to not flinch cutting hardwood at 300ipm.

Seems like the gantry might weigh as much as 75 pounds with the spindle and all the trimmings.

Would twin 400w motors be enough for that? Or should it be more.

I feel like I lack the mathematical wherewithal to figure this out.

Thanks!

Max

[ger21]

With those ballscrews, you'll need 1500 rpm to get 300ipm. Screw whip may be an issue. You won't need a lot of torque to get a lot of power, but you might need more to overcome the inertia of that long screw.

If your gantry only weighs 75 lbs, including the spindle and Z axis, it'll probably flex like a wet noodle. 75 lbs is extremely light for a gantry on a 4x8 machine.

[Richmaple]

You said it has 20mm ballscrews?! I was asking about pitch (is that diameter you posted, instead?). Ger21 might know something I don't, and I certainly appreciate his input, but I don't agree with the numbers. He said 1500rpm would get you 300ipm but if you have 20mm ballscrews, 1500rpm would get you 1500*20mm = 30,000 mm per minute = 1181 ipm which is way, way fast. But to be honest, I'm doubting that machine has 20mm pitch screws. 5mm or 10mm seems way more likely.

At any rate, first off, teknic for free has a great service that will answer this question much better than we will. It would help just know gantry weight, perhaps by asking VXB.

Second, if this is like my avid machine, the 2 drives that move the gantry don't move (they're attached to the base area) which means you don't pay a penalty for the weight of those drives. Unlike the X and Z drives, btw. Just something to consider.

Lastly, Teknic allows you to swap drives within 90 days of purchase and all you pay is shipping. It's legit, and I've actualy done that. Yes, shipping can be ~$100 but that's not a lot to be able to choose a different servo if you made the wrong choice, especially since there would be no effect on wiring, etc. So I advise you buy the servos when your machine is nearly done so that you have a large % of those 90 days left to see if you dont' have enough power or speed, etc, and you can swap.

hope this helps and best of luck!

[ger21]

2005 screws - 20mm - 5mm pitch

[Teknic_Servo]

Hi southpaw: I’m an engineer at Teknic. We would be happy to help you size your motors. Ideally, you would be able to provide us the length, diameter and pitch of the screws; the weight of each axis; and your performance goals (cutting and rapid speeds, etc.). If you have most of this data, but not all of it, we can probably still help, but we’d likely need to give you a range of motors to consider.

And, like Richmaple said, we do allow you to return motors within 90 days (even if heavily used) for a full refund (less shipping). This gives you a safety valve in case you happen to choose a motor that’s too small or unnecessarily large for your needs.

As a side note, there are diagnostic tools within our software that will allow you to see how hard you’re pushing each motor, so you can quantitatively determine how good of a fit the motor is for your machine. See this video for an example of how this software can be used:

You can contact us at 585-784-7454 or through our website contact page: https://www.teknic.com/contact/

Best regards,
Ian R, Teknic Servo Systems Engineer

[joeavaerage]

Hi,
if you look at the Clearpath SDSK range you will find that the prices are all much of a muchness at the 350W-400W level.
If you want more power then there is a BIG jump in price for 750W-900W.

I use 750W Delta B2 series (160,000 cpr encoder), and they are cheaper than a 350W Clearpath. Double the power for about
the same dollar value........

Craig

[southpaw]

No question, the Clearpath motors are not the cheapest ones out there for the power output or torque curve. But given that I'm a novice getting into building, the ease of installation and integration of motor + drive are worth their weight in gold for me. Also, if you haven't checked it out their diagnostic software for getting up and running looks really impressive with all sorts of diagnostic tools.

To top it all off, I gave Ian at Teknic a call and he patiently walked me through his thoughts on what my best options are and the pros and cons of each. This kind of customer support is what I look for in a company and makes it a crystal clear decision for me as a builder and consumer. Thanks, Ian! Super excited to continue with my build.

[joeavaerage]

Hi,
I have no disagreement with what you have said...... but I refuse to pay approx $500 for a 400W servo when for the same money I can get a 750W servo with a much better encoder, vastly better
IO, vastly better and flexible control and signalling modes.......and I don't care if Clearpaths come with 'dancing girls' they're too bloody expensive.

Craig

[XYZGnomon]

Using CPM-SDSK-3411S-ELS with my Avid benchtop pro 2x3, which is at least similar in that it's a ballscrews driven gantry cnc. Tons of power but you'd need a different model depending on what your ballscrew pitch is and how heavy your gantry is, etc.

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I am planning on buying an Avid Benchtop Pro 2x3 myself! I am a CNC machinist but I've never had to build a machine's electrics before. I quite like the idea of Avid's control cabinet and port integration, but I'm also into having servos with encoders if that's a possibility. Are there ready-made control systems for these servos that are preconfigured for Avid? If not, how did you do yours?

[Richmaple]

>>Are there ready-made control systems for these servos that are preconfigured for Avid? If not, how did you do yours?

You may get better responses with a new thread since it's a new question, but in case it helps, I have clearpaths on my Avid Benchtop Pro and used a Centroid Acorn board to make my own control box. You dont need much more since the clearpaths take step and direction pulses right from the Acorn. That said, it was easily tens of hours of tapping holes in the control box backplane for DIN rails, doing the wiring, once you count the contactor, estops, limit switches, and sundry other odds and ends (like 2 powered, switched outlets from outputs on the acorn, etc etc). The "config" part in Centroid was pretty easy for the record, and probably less than 5% of the total time to do the physical stuff. Don't know if somebody makes one that's plug and play because I wanted to make my own anyway and glad I did. But I was optimizing for learning the most and having it the way I wanted it and not for speed or convenience.

[MARV]

I'll second Richmaple's sentiments. I also have Clearpaths on my Avid based machine (4824 Pro). Had to make my own control (ESS/MB3/Mach4) and it was a bit of a task. I'm a woodworker and my CNC was to be another capable tool in the shop.

I think what some are missing here is a variable in the value equation; personal knowledge of mechanical/electrical bits necessary to complete a working machine. Having access to the knowledge base at Teknic was worth a great deal to me and their servos have proven their worth. And that's not to say other components might have been better or worse. My machine is now functioning as I had envisioned and that's what is important.