Machsupport Forum

Mach Discussion => General Mach Discussion => Topic started by: yahuie on August 30, 2007, 04:30:24 PM

Title: retrofit - steppers or servos?
Post by: yahuie on August 30, 2007, 04:30:24 PM

I am finally ready to do my first mach retrofit.  After considering retrofitting a machining center, I'm stepping back and am going to retrofit a Shizuoka cnc knee mill.  It currently has steppers on it which are nice and mounted and obviously the drivers for it, etc.  I am tempted to use those.  For step angle, it says I.8 (is the "I" really a "1" ??).  The brand is rapidsyn on the motors, the enclosure says "the Hasbach company" and the manuals say Allen Bradley. 

So I guess I have two questions:
1) Can and should I use the existing stepper motors.
2) Can and should I use the existing stepper drivers?


Title: Re: retrofit - steppers or servos?
Post by: zarzul on August 31, 2007, 11:07:19 AM

The I is most likely a 1.  1.8 deg step is most common, that gives you 200 steps for 1 full rotation of the shaft. 

Can you take some pictures of the machine? 

I would  try to use the existing components, they are most likely to be correctly sized for the equipment, all you have to do is to figure out how to interface it.

Do you have any schematics, or part numbers on the Allen Bradley parts. 

Get some more part numbers and info.  maybe we can help.


Title: Re: retrofit - steppers or servos?
Post by: yahuie on August 31, 2007, 01:38:26 PM

First of all, thanks. 
I have a Galil controller, and access to several servo motors and drives, so that option is tempting as well....
Now for the info I found. 
It appears I have a Bandit Controller.  Probably a bandit Level II.  The model number on the rapidsyn motors is 2D-112-101AS.  I took a number of pictures that I hope are helpful. 
The current is 3.1A. 
The Voltage is 4.6 VDC.

I couldn't make out the rpm. 
The model on the driver is 214 072 01 D 

I do not appear to have any schematics for this machine - only for bandit III which may be very similar.

I have schematics for the 214 076 21 drivers (from Bandit III).

I have attached several photos.
Title: Re: retrofit - steppers or servos?
Post by: zarzul on August 31, 2007, 04:06:39 PM

Looks like a great project, lots of work though.    Good job on the pictures,  the drivers I assume are the 3 boards on the right side of the picture.

The driver schematic is probably the most important part,  if there is a way to inject the step and direction signals into it then you are halfway there, and you would be able to abandon the rest of the controller.

Can you post those somewhere or send them to me off list, if you can scan them.

Title: Re: retrofit - steppers or servos?
Post by: jastein on August 31, 2007, 10:49:32 PM
Hi Bill: I have a Shizuoka mill that same size that originally came with servo motors. I converted it to Mach control a few years ago.  it replaced a Bridgeport Series II which had stepper motors and an ah-ha control.

The servo upgrade involved adding encoders to the motors as they used resolvers and building timing belt reduction drives to let the motors run faster as they had originally been direct drive as are your steppers.  The machine is now running great with Gecko 320 drives.   It took a while to get all the bugs out.

I think I would stay with the steppers If I were you. Perhaps you can use the bandit power supply as I think they are around 80 volts and just get some Gecko stepper drives.  A good breakout board will same loads of work. 

Let me know if I can help if you decide to go with the servos as I can post some pictures of the belt reduction drives.

Anyone looking for a Bandit III for servos?? Includes the tool change M function board!!??

Title: Re: retrofit - steppers or servos?
Post by: yahuie on August 31, 2007, 11:15:46 PM

Thanks for the info.  Any feel for what kind of performance difference there will be between steppers and servos?  Speed, smootheness of cut, reliability...  Also, if I do use steppers, are there cheaper (but still reliable) solutions than the geckos?   I see a lot on ebay.

Is the main problem with the servo solution making the timing belt reducer? 
If I use the stepper motors that are on there, can I do microstepping?  How will I be able to wire them up without wiring diagrams.

Anybody have the schematics for a Bandit II?

Title: Re: retrofit - steppers or servos?
Post by: jastein on September 01, 2007, 12:11:32 AM

If you are concerned with the cost of the Gecko stepper drives, they are a lot less than all the fuss with the servos!   The cog belts and pulleys (gates), encoders, and all the various wiring issues (noise) in addition to the cost of time to build the reducers is very substantial. Makes a set of Gecko 210 look almost free!

To tell you the truth, when I was using the Bridgeport with steppers (microstepping) the only thing lacking was the rapid traverse speed.  When cutting steel at least, the speed is well within the capability of a stepper!!

The only drawback to steppers with a big machine like this is that  you really have to watch your accellerations to avoid loosing steps. I have even had to be careful with accelleration using 40 in-lb servo on the Y axis because it is really more than the Gecko 320 should be doing. It would be nice to have ac servos but they are pretty pricey, like $1k per axis with the drive

You can just figure the stepper coils out with a ohm meter. It is pretty simple if it is a 4 wire motor. I am sure there is someone out out in Mach land that could tell you how even if it is a 6 or8 wire.

I can look later on as I think there might be a Bandit stepper schematic with all the books that came with my mill.

Title: Re: retrofit - steppers or servos?
Post by: yahuie on September 01, 2007, 01:53:33 AM
So I'm pretty convinced to go with steppers but would like to re-use the drives if possible.  I have some emails out to find the wiring schematics (I'm not sure yours will help since I have steppers on mine - thanks though).  If I go with the gecko's it's hard to figure out which model driver to use.  Is the "short circuit protection" offered by the 212's worth it? 

Title: Re: retrofit - steppers or servos?
Post by: yahuie on October 04, 2007, 12:46:08 PM
I am going with steppers and trying to reuse the power supply components as suggested.  Those components are: 1 multitap transformer, four power capacitors, three bridge rectifiers, and three regulators.  I am confused though because I looked up the regulators' voltages and the highest voltage regulator is for 14 Volts.  I have Gecko 203V drives which say the voltage should be between 4 and 20 times the rated voltage of my motors which is 4.6 Volts.  That makes a minimum of  18.4 Volts.  Any ideas on how to proceed?


Title: Re: retrofit - steppers or servos?
Post by: zarzul on October 04, 2007, 12:57:46 PM
The power to drive the gecko's doesn't need to be regulated.  Skip the regulators,  all you need is to determine the outputs on your transformer (you will want the voltage in the range you are looking for & current capacity), run that to your rectifier, put your output across large filtering capacitors and feed your Gecko's.  You will need a regulated 5volts for signal/controls, you may be able to pick that up from the other multi-taps on the transformer and put that through a 5 v regulator.

No luck finding a schematic on the driver boards?

Maybe a high quality picture of one both sides, good enough resolution to make out the chip numbers and wire traces, would enable someone to determine if their is a point to inject a step /direction signal into it without buying a bunch of new hardware.

I would be willing to take a look.