**RESOLVED** Reusing my servo motors

[chris.poirier]

If I can get some assistance in determining if I can reuse my servos I'll purchase a kit immediately.

I have an older Supermax knee mill with a Bandit II control.
The X and Z servos were original to the Bandit install (Danetics), the Y is a replacement Baldor.
Encoders are 500 line.

Can I reuse my servos with the MPU11/DC310 kit and new encoders?
What parameters will determine if my servos will run properly once installed and will Not damage the drive.
I may be able to get original documentation from the previous owner.

Thanks,
Chris

[Centroid_Tech]

Chris,

What are the voltage and current spec's on your existing motors?

In most cases people are able to reuse their servo motors by installing new encoders.

If you look at your motors and provide the necessary information I will be able to let you know if they work or not.

Ajax Tech

[chris.poirier]

Here is the servo info from the tags.

X and Z servo are the same:
Danetics: PN557-642-70
500oz-inch
100VDC
10A cont. current
39A max pulse
No load RPM 2500
Voltage constant 40V/KRPM

Y Servo
Baldor MTE-4070-BLACE (BLACE was hard to read)
28 in-lb
cont current: 9.2
Peak 37
Max rpm 2500
Voltage constant 40v/krpm

Chris

[diycncscott]

Hi Chris,

Your existing motors and servo power supply should be fine, your encoders will most likely need to be replaced.

The good news:
Current range on all motors is well within our 15amp continuous spec.
We have used similar Baldor motors as our production motors in the past
The max RPM for these motors is 2500rpm
The Volts per thousand RPM for both is ~40V/K, this indicates a servo bus voltage of ~100VDC -well within our acceptable range

The bad news:
Your encoders are 500 line = 2000 count per rev. Even at 10 revs per inch that's only 10,000 counts per inch resolution.
Our minimum recommended resolution is 20,000 per inch.

More good news:
Replacing your current encoders with our standard encoder will increase the resolution of your system by a factor of 4.
Encoders are $155.00ea.

If you have any further questions, please feel free to call 814-353-9218

Regards

Scott

[chris.poirier]

I took my servos out and pulled the encoders.
Damaged my tach on one motor. I don't need it correct? The designer for Danetics must have been and electrical engineer, what a pain to get apart.
My shafts are 1/4 inch. can you send me the mechanical drawing of encoder you sell so I can see what I am going to have to make/purchase in order to use them.
Also can you give me a source for purchasing brushes for my servos? They look standard.

I will call you to firm up the details and order everything once I go through the check out procedure for my servos.

Best regards,
Chris Poirier
chris.poirier@verizon.net

[diycncscott]

Hi,

No need for the tachs -velocity is derived from the encoders.

Encoder drawing:

[CNCguy]

Chris wrote> "Also can you give me a source for purchasing brushes for my servos? "

Are you sure your brushes really need replacing?
If not , it is best not to mess with them.
Contrary to popular opinion, brushes on DC motors used in CNC equipment don't wear much.
The urban legend of brush wear arises because of most everyone's experience with AC brush motors in hand drills, saws , routers, hand grinders etc, those brushes do wear out, think about how many revs they turn in such a short time.
Most DC motor brushes never need replaced on a CNC machine because the actually run so little, 10 years use on a CNC machine is still within the life expectancy of most brushes. Unless the carbon is worn down to near where the wire goes on or worn to the point that the spring will no longer push the brush up against the commutator, the brushes are probably fine. CNC axis motor brushes don't wear out (Well they could , but its very rare) .

One other warning, don't take any servo motor apart,doing so may ruin the motor. Please see the following link:
http://www.ajaxcnc.com/ajaxbb/viewtopic ... ushes#p342

[chris.poirier]

I pulled the brushes on my X just to take a look. Seems there is enough material left. Did this before readinbg your post.
I'll leave the rest alone and just finish the checkout using a DVM per the tech note on how to check the servos. I have done a lot of trasmision work in the past and these motors don't realy scare me. But having said that I also belive in if it ain't broke..... Thanks for the heads up.
Chris