Re: Servo's and Power supplies

Hi, I have a few of the same type of motor. Those motors are wound for
torque and they max out at about 1200rpm. They will probably be ok if
directly coupled to your ballscrews. It could be that a 2:1 reduction
will give better overall performance, not only in torque, but in
faster accellerations. Fast accellerations could win out over high
rapid speed to speed up cutting time. How often will the machine ever
hit 240ipm anyway. Hard to say which is the better method. I am
temporarily going the direct coupled way for the same reasons you are.
Should have X and Y done next week.

As far as power supplies go, you might want to go with as high as a
55V supply. Since servo drives are only about 85% efficient (just a
guess), you can take 15% right off the top. 55V x .85= 46.75V (to the
motors). Then when you set up the "maximum steps per second" in your
software, keep increasing while monitoring the voltage to the motor.
When it hits about 38V, you know you are getting as much out of the
motors as they are capable of. I am only speaking from experiance and
I have found that my machines allways perform better if I start with
higher than rated voltages and meter it down in software.

As an extreme example, I am temporarily testing a new 74V controller
using G340s on my router. It uses the 1kw beast power suply from
www.cnckits.com. My motors are rated at 24V. I set the max speed to
200ipm and the voltage to the motors never exceeds 28 which is within
reason. This thing really flies. Way more speed and torque than when
it is running on its own 30V transformer. The lead screws are turning
at 2000rpm and luckily dont shake themselves apart. The max reliable
speed I can get using the 30V transformer is 120ipm.

Dean








Coul --- In CAD_CAM_EDM_DRO@yahoogroups.com, "Jason Cox"
<sinergy@o...> wrote:

> Hello,
>
> I am currently working on a power supply to drive 3 servo motors and

have a couple of questions and would appreciate any help!

>
> The motors I have are 600oz/in from camtronics, and are rated at

38vdc 12amps max.

>
> 1. I am looking at a toroidal transformer and in my price range I

can reall only afford a 500va transformer. There are two I am looking
at, a 25vac 20amp or a 30vac 14amp.

>
> The 25vac will give me about 35vdc at 20a, and this is the one I am

leaning toward. My question is will there be any downside to running
my motors at 35vdc rather than 38volts or even higher? From what I can
tell I will only lose rpm and the toqrue is in the amps, is this
correct or am I way off?

>
> Im not even sure if 20a will be enough to power all three motors I

plan to do alot of 3d contouring. The machine I am retrofitting is an
RF-45 mill drill and I am driving the head rather than the quill, it
is fitted with 5/8" ballscrews x & y and 1" ballscrew in the column. I
am planning to connect x & y direct to the leadscrew and am undecided
with the z axis. I am hoping to counter balance the head. Oh, and all
leadscrews have .2in lead. Is the direct connection of the motors a
bad idea? Its just more simple and cheap for me at the moment.

>
> 2. The second question I have is as to the protection of my power

supply, firstly the capacitor I am planning to use is a 47000uf 40v
not quite 20% higher voltage as geckodrive suggest, will this be a
problem? And secondly I hear of bad things happening during
deceleration of motors, how do I protect my power supply against this.

> I am running 3x gecko 320's.
>
> Thanks for any help, the list has been great reading and has helped

me get this far!

>
> Jason Cox.
>
>
>
> [Non-text portions of this message have been removed]