Help determining Servo Motor size

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Bill87068
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Help determining Servo Motor size

Post by Bill87068 »

I am wanting to upgrade an old Series II Bridgeport with a Dynapath CNC conversion on it already that I picked up at auction the other day. Challenge I am having is the XY servo motors do not have any markings or stickers. Based on the electronics in the cabinet they are DC motors and looks like there is an 80VAC transformer upstream from the DC rectifiers.

Is there anyway to tell or measure what the torque rating of these servos is or the max current draw so that I can make sure to order the right board and get it set up correctly? The case on the motors is about 5”dia and just want to make sure they won’t pull over 15 amps. I assume I could just use the 80VAC transformer and feed that into the Allin1DC rectifier and be ok???

The factory power quill looks to be 1.8amps at 90-100Vdc so I am good there with the Allin1DC but there is no encoder on it that I can see.


I have also considered going with the Acorn and just buying a pair of stepper motors and running 2 axis open loop to save some money. Heck I don’t even know if anything other then the spindle works yet. I am just a hobbyist building basic brackets and such and not sure i would ever need or use the third axis as CNC.
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polaraligned
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Re: Help determining Servo Motor size

Post by polaraligned »

Dynapath is still around and may still support your control if you choose to repair it.

The All-in-one will run 40 in-lb motors which is larger than the common 29 in-lb servos that are used on this class of mill, so I have no doubts that the All-in-one would be fine.

Are there suitable encoders installed on this machine? Are they under that cover that is inline with the leadscrew?

I personally would thoroughly evaluate the iron before making a big investment into an old machine.
Bill87068
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Re: Help determining Servo Motor size

Post by Bill87068 »

Thanks and trying to make an evaluation before I spend any more money is exactly what I am I. The process of. :). The ways and screws appear tight. It’s got some electrical issues and I let the smoke out of the factory controller board of which I am not sure why yet.

Can anyone tell me what’s the device mounted on the back of the servo motors that can be seen in the first photo. It has two wires coming off it. Tach? Direction indicator? Would that allow me to use the Acorn with these servos?

There are encoders on the lead screws for XY (photo attached). I can not seem to locate them on the web. Looks like NPL 2300-C5-0500-00. Guessing they are old and low res so figured I would be replacing them.
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polaraligned
Posts: 197
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Re: Help determining Servo Motor size

Post by polaraligned »

Yeah, that would be a tach on the motor. You don't need them with the Centroid. The encoders are probably at least 1000 line which is ok. You just have to confirm that they are differential output. I can't find anything on them either, but you can get new ones from Automation Direct for about $100 each. You just may need to make an adapter for them to fit.

Was this machine refitted with ballscrews?
A better picture of the info on the encoders *may* help to determine if they are ok. I can't make out most of the writing on them.
cncsnw
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Re: Help determining Servo Motor size

Post by cncsnw »

I would be willing to bet that the "-0500-" in the old part number indicates they have 500 lines. It is probably not worth figuring out how to connect them, when they can be replaced with much better ones for a couple hundred dollars.
Bill87068
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Re: Help determining Servo Motor size

Post by Bill87068 »

Yes it does have ball screws.
martyscncgarage
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Re: Help determining Servo Motor size

Post by martyscncgarage »

How about pictures of the existing control cabinet?
Pictures of the transformer and the rectifier/filter capacitor (BIG beer can sized capacitor)
Can you power up the cabinet? Then you may be able determine DC buss voltage by measuring DC voltage across the big capacitor.
Do you have basic electrical/electronic experience? Have you done a CNC Conversion before?

As Marc mentioned, you will need new encoders. Another member is currently doing a conversion with encoders mounted similarly to yours.
"Milltronics MB24"

Marty
Reminder, for support please follow this post: viewtopic.php?f=20&t=383
We can't "SEE" what you see...
Mesa, AZ
Bill87068
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Re: Help determining Servo Motor size

Post by Bill87068 »

Attached are a couple photos that of the control cabinet.

The transformer powering the Ac/DC converter is the big black on with the 80VAC sticker on it. Looks like the input of that transformer is across L2 and L3 so I can simply connect the input of that transformer straight to the house 220 panel to get the voltage measurement across the cap. And even across wires on terminals 1-2 which feed the X axis servo motor if I can make the controls function.

I have never done any automated controls or mill conversions and am admittedly an”mechanical” guy but have decent confidence in electrical stuff and with some high level guidance from you guys am confident we can make this work :).
Attachments
015FA9D4-B8D6-4E82-90C4-C69BD776A307.jpeg
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martyscncgarage
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Location: Mesa, AZ

Re: Help determining Servo Motor size

Post by martyscncgarage »

80VAC*1.414=113.2VDC. That is your buss voltage
The motors appear to me to be typical SEM motors. I would bet they are 29in-lb motors.

You should test the servos themselves using this tech bulletin:
https://www.centroidcnc.com/dealersuppo ... ds/155.pdf

Take a look at the attached schematic and see if you can follow it. This is most likely the one to use for your machine.
You keep the 80VAC transformer and you could keep the filter capacitor and bridge rectifier.

Read the All in One DC Installation manual for reference and if you go to YouTube, search martyscncgarage All in One DC, you might watch the videos to see what you might be getting into. All that info can be found on this page:
https://www.centroidcnc.com/centroid_di ... oller.html

The flip side, you could buy new AC servos and replace the old brush servos. If you buy ones that take step and direction you could use Acorn as many have done. You won't have true closed loop motion control but the drives will close the loop. (If the mill has handwheels and you manually move the mill, the DRO's will not change)

Once you buy All in One DC, you have to stick with DC Servos. AIO DC is however a true closed loop motion controller.

How about some pictures of your machine? Home hobby use?

Marty
Attachments
S14746 Mill, 220 110VAC, ALLIN1DC, 83VAC Stepdown Transformer, Inverter (VFD).pdf
(2.59 MiB) Downloaded 22 times
Reminder, for support please follow this post: viewtopic.php?f=20&t=383
We can't "SEE" what you see...
Mesa, AZ
Bill87068
Posts: 7
Joined: Fri Sep 10, 2021 10:49 pm
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Re: Help determining Servo Motor size

Post by Bill87068 »

Thanks for the responses. I was able to power up the input to the step down transformer and confirmed 81VAC out and 109VDC at the capacitor (I think it’s a touch lower then calculated value as there is a bleed down resistor across it. I have not pulled it and measured it yet to confirm). I was able to operate both X/Y servo motors as well. X motor is pulled off the machine and draws 11+ amps of inrush current and about 0.8 amp at steady state no load at the full 109V.

Marty thanks for pointing me to all your videos. I have watched a couple of them and as I continue thru this project no doubt will watch them again.

I am kind of leaning staying closed loop and going with the ALlIn -DC. If. I nothing else just for the simplicity of it since servos are already installed. One thing I need to still determine is the power quill servo feed voltage. If it happens to be close to the same as the X/Y servos I may really be in luck. I have powered it from an external 110VAC power and it does function off the front panel so just a matter of some measurements
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