Re: Servo's and Power supplies

--- 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?

Don't forget the 2 diode drops in your calculation; your 25vac comes
out at less than 34 volts. Also as you draw load, that figure will
drop as the capacitors discharge.

If you don't have the volts you can't draw the amps. The electrical
analogy to torque is watts and is V*V / R.

I run the same motors at 42 VDC.

>
> 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.

Without knowing the details about the RF. I haven't heard of anyone
on this group directly coupling servo's, most of us seem to run 2:1
reduction on X & Y and larger reductions on the knee. Servos require
to work well into the speed range to develop usable torque.

>
> 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.

40 Volt working caps are too close to your target volts, especially
when the motors declerate. Don't forget the 470uF UPW caps direct
across the Gecko power terminals. Have a look at your local Goodwil
computer shop, I found a big old UPS that had a 32 volt transformer
rated at 1500 watt.

>
> 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]