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03-26-2008, 04:56 AM #1
Retrofit of 10EE Drive to AC Brushless Servo Motor
I mentioned in an earlier thread that I am converting my 10EEs drive from motor generator to AC Brushless Servo. Finally have gotten started on it.
I now have all the parts for the motor. I am using a 2kw Mitsubishi Servo with a 3.5kw control. Got the control, encoder cable, and the motor off ebay. The motor appears to be brand new, no marks around the holes from being mounted. The control was sold as having been repaired a year ago and sitting on the shelf as a spare. Went to power it up and it went boom! Opened it up and it had been repaired but whatever this drive was installed on corroded some of the PCB tracks in the DC Bus and it flashed over. Cleaned it up, installed new caps, and sealed the board and it works like new.
The drive is intended to be operated with three phase. So while I was in there I changed the caps to a higher capacity. This combined with the drives ability to run on Japanese 200v mains I think I should not have any problem driving the smaller motor.
Last week the special interface connectors showed up. Got the drive running in velocity mode. It also has a position mode where it will accept step/direction signals to control the motor. In vel mode it has a max speed of 2100 RPM and with the pot I am using 8-9 RPM minimum. Incredible power at slow speed. Guess thats why it has that 35mm dia output shaft!
I have decided to direct drive the back gear. If I need to get that extra 400 RPM I will make a larger drive pulley for the gearbox. Or snag the 3000 RPM version of this motor if one pops up on ebay. Today I drew up the adapter plate that will adapt the gearbox and give it a mounting face identical to my servo motor. It will hold the input bearing, oil seal, and drive shaft.
I happen to have a plate of cast iron that will be perfect for this. about 10"x10" and 1.625" thick. I faced it off on the mill and it looks good. Going to make the drive shaft from a piece of 4142. it will be hard coupled to the motor. One modification from the original design is the addition of a pilot bearing on the tip of the drive shaft that will run in the output shaft of the gearbox. This will allow me to use other coupling methods than a hard couple if I have problems. Also I can belt drive the gearbox if this dosnt pan out.
Heres some pics of what I have going so far. The first pic is of the motors I have. The motor I am using is the one on the right. To get an idea of size the shaft is 35mm (1-3/8") and the flange is 176mm sq.
The other pics are of the design of the adapter and the facing of the cast iron.
03-26-2008, 04:57 AM #2
03-29-2008, 01:08 PM #3The drive is intended to be operated with three phase. So while I was in there I changed the caps to a higher capacity. This combined with the drives ability to run on Japanese 200v mains I think I should not have any problem driving the smaller motor.
Sorry, I'm not trying to be difficult; guess I just haven't had enough coffee yet this morning.
03-29-2008, 02:17 PM #4
..Also what is the model number of the drive you are using?
I have a couple of brand new motors left over from a retrofit.
03-29-2008, 03:40 PM #5
Thanks for posting this, I'm all eyes on this one.
How much do you have invested in parts so far?
Are you going to complete this soon? I'll be watching intently...
03-29-2008, 05:17 PM #6
What was the reason for the conversion?
03-29-2008, 06:21 PM #7
This week I stalled my 3kW VFD a few times at low revs. I don't know what the power-rpm curve is for an ordinary vfd operated motor.
So at first I thought 2kW is not much, but if a servo makes it available on the whole range It probably should be sufficient.
03-29-2008, 07:59 PM #8
AC servos are a much different creature...with closed loop feedback for commutation, the motor has best possible torque at all speeds, not flat mind you, but pretty good.
the graph below is for the motor in my 10EE, it is actually a ~4.5kW unit, 30NM with medium rotor inertia. it can easily bring my spindle to a stop within a part rotation at any reasonable threading speeds and has more than adequate torque for any cut I would expect this lathe to take.
Jerry's conversion should open some interesting possibilities for him. with a 2kW motor, he might need to run the motor into the intermittent range for heavier cuts and inertia mismatch might cause some grief but nothing that can't be worked out.
03-31-2008, 04:52 AM #9
Yesterday and today I got a little farther on the adapter plate. Dumped the file into mastercam and made the toolpaths. First one came out wierd and didnt notice until it milled where it shouldnt have. Then the mill started reading a speed much lower than what it was running at and I killed three cutters before I figured out whats going on. Also had this annoying bug where the machine was randomly e-stopping by itself. So it took a whole lot longer to machine than it should have.
But the back half is done. Need to do the paths for the other side and finish it off.
The drive is the MR-J series drive. The motor intended to run on it is a 3.5kw servo. I have not been able to find one so I am using the 2.0kw motor. Same series so they are pretty much compatible. I will just use the torque set feature to limit max current.
The specs for this motor show a totally flat power curve from dead stop to full speed. 9.5Nm continous and 28.5Nm peak. Medium rotor inertia. Then the drive is software limited so it wont run past 2100 RPM. It might run faster in position mode but I am not really worried about it. I am not worried about the power. It is pretty close to the specs of the original motor (3hp). I mean, this is technically a 10" lathe. How much power do you need?
The machine will run off 200-240v single or three phase. With the phase converter and lathe idling it pulls 20 Amps out of the wall so that should drop down to nothing once I do the conversion. I am also thinking of doing a partial CNC conversion to make an electronic leadscrew and taper attachment. I have another little mitsubishi 200W motor and MR-J2 control for the X and I am looking for a 400 to 750w motor for the Z.
So far I have spent $40 +S&H on the two drives (Used, one rebuilt), ~$25 for new caps for the drive, ~$70 for the encoder cable(NEW). $50 for the interface connectors(NEW), $70 + $50S&H for the motor (Appears to be NOS).
Thats about it so far. Still need to pick up a coupling. Not sure if I am going to use a rigid one or a two piece one like a lovejoy.
04-01-2008, 10:36 PM #10
Finished up the adapter plate this afternoon. Came out well... except for the two "dings" where I learned about a couple quirks in mach. But no one will ever see them again.
Machined both sides and set it on the rubber mat and gave it a whack and it separated. Knocked off the burrs with a file and thats pretty much it. The bearing I have has a groove and hole around the race for allowing it to be greased so i will probably drill a hole through the side of the casting and tap for a zerk.
Next up is the shaft. Got a piece of 1-1/2" 4142 ready for that.
04-01-2008, 11:11 PM #11
Wow, nice work, this is a very interesting thread.
What is the advantage to converting over to AC from a DC motor generator? Seems most people want to get away from tubes, and the DC motor generator seems like a good think in comparison. Hoping some of you more educated folks could explain why.
04-01-2008, 11:25 PM #12
Little or no noise, less current draw, faster accel and decel, less maintenance, better low end power, less weight.
Also allows you to do some possibly interesting things like CSS and electronic leadscrew much easier than with the original drive since these drives can be controlled by logic level voltages or analog voltage input. Pretty simple to interface it to a computer.
04-01-2008, 11:52 PM #13
I hear you on the noise!
I've been ponderin' if I want to change a small south bend I got to 3 phase, as if I do I will need to listen to the RPC running while I use it. Thinking of leaving it 1 phase...
However, the interfacing piece sounds like a big plus in today's world.
04-02-2008, 12:10 AM #14
Am I the only one surprised by the void in that CI plate, not visible but a line in the first photo, large in the second, and Wow in the third. I rarely deal with as cast material, so I don't get to seen things like that.
04-02-2008, 01:21 AM #15
I really dont know where the slab came from but it looks like from the draft in the plate that it was poured vertical and that bubble formed after it cooled. Still a pretty big bubble. The cast actually machined pretty nice like some of the ductile some of my model engine parts came in.
04-02-2008, 02:56 AM #16
This is an interesting thread on conversion of the EE..The above adapter was made from a 1 piece 6061 Al.
Thought I would post in case someone might want to go this route. It weights about 10 pounds.
04-02-2008, 05:23 AM #17
Wow, looks nice. That chunk of aluminum must of cost a fortune!
And created a drum worth of turnings and chips!
One thing though. I see you left a boss to index to the gear box housing. On the spare motor I have I found that that hole was not concentric to the shaft so you might run into some alignment issues there.
04-04-2008, 04:19 AM #18
Since there is a good bit of servo motor expertise posted on this thread, I have a question:
I have a new surplus Sanyo-Denki 3.5kW servo motor. P60 series. It is unfortunately not a stock model so instead of the usual 2000 line incremental encoder, it has an absolute encoder.
All the servo drives I have are for use with incremental encoders. Any suggestions for an appropriate drive with step and direction input?
04-04-2008, 05:14 AM #19
There probably is/was a dedicated drive for that specific motor. A lot of the japanese stuff is like that. There is a possibility that a section of the encoder is absolute and another incremental. Some mitsubishis seem to be that way.
Today I got the shaft done. Last night I turned it down and today I put the keyways in and drilled and tapped for retaining the key.
Started on the design to hold the motor. Got a bunch of 1/2" aluminum scrap plate to build it out of.
04-06-2008, 01:17 AM #20
Made some more progress last night and today. Cut the parts out for the motor base out on the mill yesterday and welded them all together today.
Tried tig but 300 amps was not going to cut it for 1/2"aluminum so I pulled out the spoolgun. After a few hours of fighting feed issue do to not having enough new tips I finally got it together. Must of cut out some of the welds 4 times before I finally got a decent bead. Need to clean it up and paint everything. Used my XMT-304.
Need to clean it up and paint everything.
I have a bellows type motor coupling on its way. Should be here next week sometime. Maybe next weekend I will be able to get it installed.