SERVO MOTOR SIZE?

[jshank]

Has anyone used the Keling KL34-180-90 (NEMA 34)servo motor on a Bridgeport cnc series 1 machine. I am not sure this servo is powerfull enough for direct drive or 2:1. The spec for this motor are as follows:
Constant Torque: 1.6 N-m ( 226 oz-in)
Peak Torque: 8.0 N-m ( 1125 oz-in)
Max Speed at Voltage Constant: 3200 RPM
Terminal Voltage: 90V
Constant Current: 7.8A
Peak Current: 40A
torque Constant (KT): 0.182 NM/am
Voltage Constant (KE) 18.95 V/rpm
Resistance: 0.925 ohm
Inductance: 2.5 mh
Inertia: 3.4 kg/cm^2
Thanks
Jeff

[TOTALLYRC]

Here is the specs of the SEM motors I picked up from ebay to replace the old motore on my mill and have backups.


MFG: SEM

Type: MTS30H4-28
C.Stall Torque 19 LB/IN. 7.9A
MAX: 4000 RPM 112 V 43 A


I put one on the z so far and it is stupid fast.
It is a 4 brush motor and looks like it will do a great job on the other 2 axis.
At $25.00/ea plus shipping I couldn't pass them up.
Hope this helps.

Mike

[Al_The_Man]

I have a couple of Excello's about the same size as the BP, they use DC SEM 26LB-in (2.9N-m) at 2:1.
I am using one on as a spindle for a small lathe, that works well.
Al.

[jshank]

Al,
What is the model number of the SEM dc 26 in-lbs servo motor? There are so many servos on ebay that I am having trouble zeroing on a brand and model.
Jeff

[Al_The_Man]

Mine are MT30M4-38 with tach and miniature 500 line DRC encoder.
I believe DRC is now out of business.
Hegstler have a comparable replacement unit.
Al.

[HimyKabibble]

I just converted my knee mill (a Taiwanese BP clone) using the NEMA34's from here:

http://www.homeshopcnc.com/servo2.html

I used 2.5:1 reduction on X & Y, and 4.8:1 on the knee. X&Y give me over 100 IPM, the knee is a little marginal, only 25IPM. This is with a 70V supply, and Gecko G320s.

Regards,
Ray L.

[mc-motorsports]

What would you use to get 200ipm out of a full size knee mill? Anyone around 300ipm?

[TOTALLYRC]

Originally Posted by mc-motorsports What would you use to get 200ipm out of a full size knee mill? Anyone around 300ipm?

My btc-1 is speced from the factory to go 300ipm on th x and y and 200ipm on the z.
When gus had it it would run those numbers with the tnc151??? that he was using.

I can reliably go 125ipm on the x and y but I finally figured out what I was doing wrong when tuning the servo amps.
With the z tuned a lot closer than the other 2, it will go 225ipm with out any trouble/faulting out, but 225ipm for a total travel of 5 inches is scary.


Here is the servo that I am currently using on the Z.
Is is the same size and configuration as the X and Y.

MFG: SEM

Type: MTS30H4-28
C.Stall Torque 19 LB/IN. 7.9A
MAX: 4000 RPM 112 V 43 A


I will be trying these on the x and y as time allows.
Since the x only goes 18" total travel, I can live with it for now. Less than 9 seconds from one end to the other

I need to borrow the square wave generator again from work and retune all three drives. The manual for the drives is not at all clear but I think I have it figured out.

Of course you need to run the numbers for your machine.
Here are mine,

5tpi screws
2:1 pulley reduction
4000 max motor rpm at max volts 112. I am running 100v dc as verified by my volt meter.

I will guess and say 3500rpm in my case.

3500rpm/2belt reduction=1750screw speed max. divide by 5tpi and you get
350 ipm max theoretical speed.

Now you have to take into effect how much following error you want and how fast you want to accelerate. If I was just moving the table without regards to how it got there you can have a huge following error and it will go as fast as physically possible.

I have it set to a following error of 750 steps out of 2,000/rev = .375 of a rev following error worst case.
20,000 steps/inch. 750 steps error = 0.0075" max error at jogging speeds.
The lower the accel and the top speed, the closer the motor will be able to be to 0 following error.

My dspmc/ip control box has user settable following error and pid.
Gecko's are preset at +-128 counts

You will also have to take into account how much mass and drag are involved when moving the table.
Plus the fact that dc motors make max power at 50% max speed but only for a short time.
I think that is why bport speced 300IPM rapids on the X and Y

If I wanted to go 400 ipm, which would be a 33% increas in speed, I would need a motor that would go 33% faster or a coresponding reduction in gear ratio/ballscrew pitch. Not to mention a significant increase in servo power.

I hope I made some sense.

Mike

[mc-motorsports]

Whoa! I'll have to read that in the morning. Looks like a lot of good info. But with just a quick read through, explain how a 19oz/in motor can supply enough torque for a full size machine such as a Bridgeport Series I knee mill please. I'm missing something. I used 1800oz/in servo's with a max speed of 1000 rpm? I think? I can go 125imp, but turned it down to 100imp just to be safe because I commonly run programs "lights out" for 6 hour cycles... At that point, a little less rapid in exchange for reliability makes a lot of sense.
Thanks!
MC

[TOTALLYRC]

Originally Posted by mc-motorsports Whoa! I'll have to read that in the morning. Looks like a lot of good info. But with just a quick read through, explain how a 19oz/in motor can supply enough torque for a full size machine such as a Bridgeport Series I knee mill please. I'm missing something. I used 1800oz/in servo's with a max speed of 1000 rpm? I think? I can go 125imp, but turned it down to 100imp just to be safe because I commonly run programs "lights out" for 6 hour cycles... At that point, a little less rapid in exchange for reliability makes a lot of sense. Thanks! MC

1. 19lb/in not, 19oz in. That is 304oz/in continuous stall torque and since it will output many times that for short bursts, it moves the machine in fine fashion.

Your 1800 oz/in are probably rated absolute max, and not continous. Makes a big, big, difference in ratings.

2. I am moving the quill not the knee.

3. 1000rpm on the motor and a 2:1 reduction with a 5 tpi screw = 100 ipm. Since I don't know exactly what your machine specs are, I can't be more specific. Also the motor may be rated at 1000 max rpm, but if you are inputing more than the rated volts, it will go faster. Not usually a good idea though.

4. To use the same motor to drive the knee, I would just add more reduction into the picture say 4 or 5 to 1. You would give up some rapid speed, but reliability is the most important thing that you can have.

[jshank]

Mike,
Thanks for the detail information; this is very helpful in my understanding of the process and selection of components for the BPC-1 upgrade. What drivers are you using for these SEM motors?
Jeff

[TOTALLYRC]

Originally Posted by jshank Mike, Thanks for the detail information; this is very helpful in my understanding of the process and selection of components for the BPC-1 upgrade. What drivers are you using for these SEM motors? Jeff

I am using copley 423 servo amps. They were installed on the machine as an upgrade sometime in the past.
They can be a little difficult to tune due the owners manual being less than clear.
But I think I have them figured out. The hardest part was getting a square wave generator to tune them with. Thankfully There was one at work and I was able to borrow it. I will retune the drives when I get the other 2 motors installed.

See my build log here for pics and more info.

http://www.cnczone.com/forums/showthread.php?t=66994

Mike.