Re: Power stage

"Arne Chr. Jorgensen" wrote:

> From: "Arne Chr. Jorgensen" <instel@...>
>
> Hi,
>
> I have a question. If you should decide on what kind of power
> ratings a servo should have, what would you say ?

I'm using motors rated at 1/8 Hp, 1750 RPM, continuous. I'm allowing a
peak current about 3 - 4 times the current at that rating point. I'm using 2.5:1
reduction belt drive on a 5 TPI ballscrew to drive the X and Y axes of a Series I
Bridgeport mill. A calculation showed me that you get about 1000 LBs
of linear force from this servo (not counting any friction). It seems
plenty, although it runs out of gas at about 100 IPM, so acceleration is
weak above that.

> I am just thinking of what you would be looking for. I don't have a
> router or lathe. What motor size would most of you need ?

Depends entirely on the size of the machine, the 'heaviness' of your cuts,
and the acceleration you want.

> Second, if you should use a micro controller to make the PWM, what
> about switching frequency ? Any comments ?

Well, the PWM frequency need not be the same as the servo update rate.
A multiple might work out nicely. I'm running 100 KHz on my 'analog'
PWM servo amps. Something above 25 KHz would be nice to avoid
whining noises. A higher frequency allows smaller filter components.

Jon