Confused on a Servo Motor spec.

[countryguy]

I have a supermax YMC 30 (taper) from the 80's w/ some big Servos. I'm trying to see if the ajaxCNC aio (all in one) setup can run these. Max DC of 150. Motor Curr of 15A cont.

So far these Baldor's look like they will work 100VDC. Current of 10A but... There is one spec I'm not following and has me wondering what could use 39Amps?

Image below - Max Pulse Curr. 39A

It also appears to have an encoder which I think is 500L out (quad/diff I have been told but not confirmed yet?) and not 2K quad/diff My understanding is Ajax will sell some slip on encoders for the shafts to uplift resolution. But expensive @ $225 apiece! http://www.ajaxcnc.com/tech/downloads/schematics/MPU11/Encoder Specs.pdf

 

[JimDawson]

I think the 39 A is the equivalent of locked rotor current in an induction motor. I'm pretty sure you would never reach that value. And of course, you will have the proper fusing to protect things.) I'm pretty sure the drive you mention would work just fine.

I have never seen an encoder/tach combo like that. If the encoder is quad/diff, 500 L(ines) would equate to 2000 PPR. If it is quad/diff, it should have 6 wires coming from the encoder (Power, Gnd, A, /A, B, /B), or 8 if it has an index pulse (I, /I).

 

[dracozny]

39A is the peak amperage you could run the motor to. interestingly most motors are advertised by their peak performance values that you would normally avoid. Staying at 39A for prolonged periods of times will cause demagnetization in BLDC motors and the heat production can and will damage wiring.

As far as that encoder kit. I spent that price for 2 encoder kits from USDigital. They can get spendy depending on encoder counts, index, differential, size and mounting hardware.

 

[countryguy]

Thanks Jim! It has the 4 channels. They are clearly labeled and wired in. I just wish I could find a drop in equiv. replacement.... I guess it's not too common a shaft encoder case style. And it's from 1985~!

I hate to say Rip and Replace... But what do you think of 2000 PPR?

I think the 39 A is the equivalent of locked rotor current in an induction motor. I'm pretty sure you would never reach that value. And of course, you will have the proper fusing to protect things.) I'm pretty sure the drive you mention would work just fine.

I have never seen an encoder/tach combo like that. If the encoder is quad/diff, 500 L(ines) would equate to 2000 PPR. If it is quad/diff, it should have 6 wires coming from the encoder (Power, Gnd, A, /A, B, /B), or 8 if it has an index pulse (I, /I).

 

[dracozny]

Thanks Jim! It has the 4 channels. They are clearly labeled and wired in. I just wish I could find a drop in equiv. replacement.... I guess it's not too common a shaft encoder case style. And it's from 1985~!

I hate to say Rip and Replace... But what do you think of 2000 PPR?

depends on a few things. are you doing a belt drive or Direct coupling? with a belt drive what is the max speed you intend to run the motor after calculating your typical feed rate?

if you had a .25" pitch ball screw attached to the motor it would result in a smallest increment of .000125", if your max required speed is 2000rpm. this would only require a system capable of 66Khz which is well within a 5i25/7i77 combo capability, I'm sure any motion controller board would be able to handle it as well.

[FONT=Arial, Tahoma, Calibri, Verdana, Geneva, sans-serif]The [/FONT]limitation of the muxed encoders on the 5I25/7I77 is maximum count rate. This count rate is 2.77 MHz on the 5I25/7I77 (with encoder filter off) and 555 KHz (with encoder filter on) These (with a safety margin added) limit you to about 12000 RPM and 2400 RPM max with a 2500 line (10000 count/turn) encoder. Usually the encoder itself will limit you to lower frequencies.

As you can see with the above example, 2000 PPR is almost too accurate. If you go with a belt drive with a 2:1 ratio or more than a 500 PPR would be more than enough although in this case you also now have more points to create backlash.

With all this said, I do have a 1000 Pulse quad/diff encoders on my motors which is 4k PPR on 5mm lead screws with a 2.36:1 belt drive equals .000116" PP. Over engineered and $$ for a zx45. Just some things to consider.

 

[JimDawson]

Thanks Jim! It has the 4 channels. They are clearly labeled and wired in. I just wish I could find a drop in equiv. replacement.... I guess it's not too common a shaft encoder case style. And it's from 1985~!

I hate to say Rip and Replace... But what do you think of 2000 PPR?

I really can't see any reason to replace the existing servos/drives/encoders if they are working. I'm not sure what the motor/lead screw ratios are but the existing encoders (500 line) will give 2000 quadrature pulses per rotation of the motor. So assuming 1:1 on the motor gearing and a 0.200 pitch lead screw, that would give you 0.0001 theoretical position accuracy.

The only reason I replaced my encoders is because the stupid belt drive system for them failed, not the best engineering I have ever seen. I could have fixed it, but I wanted higher resolution anyway. Mine were not 4 channel encoders. Having said that, my preference is to have the encoder (linear measuring device) on the load (table and quill) rather than the lead screw. That way the backlash and lead screw error are non-existant. I can hold 0.0005 in 12 inches, as best as I can measure. My z-axis holds 0.0001 consistently.

I am still using the original DC servos and drives on the X and Y axis.

 

[JimDawson]

We are kind of cross posting here, so I'll post your quote in this thread.

Thanks Jim,
I'm still sorting out the insides - As it turns out, the AB Bandit III I have is missing the drivers. The original owner is not replying back w/ why or where.... So I need Drivers for the Servos. Can you suggest something for this Mill at 500Line encoders (diff quad) to 2000 PPR and if you think it's worth keeping together. Former owner noted that at 120ipm and 2000PPR is fine what we wanted.

The servo drives are missing, like not in the electrical cabinet? WOW :angry: I was under the impression you were buying a complete, running machine. Well that changes things a bit. Now it's time to look at the options.

 

[countryguy]

Need a quality lower cost driver to make this go...

Thanks Jim. This unit came missing the drives for the motors I've now found out. Can you suggest some sources?

I really can't see any reason to replace the existing servos/drives/encoders if they are working. I'm not sure what the motor/lead screw ratios are but the existing encoders (500 line) will give 2000 quadrature pulses per rotation of the motor. So assuming 1:1 on the motor gearing and a 0.200 pitch lead screw, that would give you 0.0001 theoretical position accuracy.

The only reason I replaced my encoders is because the stupid belt drive system for them failed, not the best engineering I have ever seen. I could have fixed it, but I wanted higher resolution anyway. Mine were not 4 channel encoders. Having said that, my preference is to have the encoder (linear measuring device) on the load (table and quill) rather than the lead screw. That way the backlash and lead screw error are non-existant. I can hold 0.0005 in 12 inches, as best as I can measure. My z-axis holds 0.0001 consistently.

I am still using the original DC servos and drives on the X and Y axis.

 

[JimDawson]

I just can't believe that the guy who sold the machine to you did that:veryangry:

The motors that you referenced in your other thread would work. You are really starting from scratch, so you are only limited by your budget. You have a mill with ball lead screws and that is about it. (at least I assume he left the ball screws in it) The options from there are endless. In this case, I would replace the motors with more modern equipment.

I would start out by deciding what controller software you want to use, then build up a system that is compatible. Then its a matter of deciding on BLDC or stepper motors and drives. Or use hybrid steppers, which seem to be the best of both worlds. I don't have any specific recommendations, but I will be happy to try to help evaluate anything that you come up with.


EDIT: I took a look on ebay for what I think are the original drives, I'm glad I was sitting down when I looked at the price, $1900

 

[countryguy]

Time to build... A Mill

Yeah, It's a loooonnngg Story. It seems I did not pay attention to a few things. I have some calls and emails in. We're in a good place. But- That aside- I need to move forwards and either:

• Get into some type of 10V servo drive (fincor was suggested) and use the Bandit III.
• Elect to put in closed loop stepper setup .
• Put in a Servo setup like ajaxcnc - But use 2000ppr or get into 8000ppr with hollow encoders