Re: [CAD_CAM_EDM_DRO] Re: Servos drivers + THC

Thanks for the reply Thomas,

Eerily, I was just about to email you! :^)

I noticed the THC folder on Master5 earlier - that I think you created
right? If I was using a servo for the THC, would I need an encoder to derive
positional feedback for the system? If the THC is controlled by the arc
voltage, then doesn't the loop become closed by the torch's arc voltage? Is
the THC board a complete system in it's self, or would I need to feed it's
output into an amplifier?

Many thanks!
John

> The lowest cost for that application is the DeskCNC servo card at
> $79 bucks sold by Fred
>
> http://www.cadcamcadcam.com/index.asp?PageAction=VIEWPROD&ProdID=11
>
> They do not have step multiplication. You would need step
> multipliers if the line count of the motor encoders times 4 (in
> quadrature) times gear/belt/leadscrew reductions are greater than
> your max pulses per second to move the target distance in that one
> second.
>
> Try this formula:
> V1 = target speed = max speed in IPS
> Pr = pulses/rev = Encoder line count * 4
> Pi = pulses/inch = Pr * (belt-gear ratio) * (leadscrew pitch)
>
> PPS = pulses per second needed from PC = V1 * Pi
>
> IF PPS > 45,000 THEN implement step multiplication
>
> The line count of the encoder is a very big factor here because you
> have to supply four times the line count to rotate the motor one
> revolution (Pr). Then you have to multiple that by any gear rations
> like belt reduction or leadscrews (Pi). If you do all of that and
> find you need 45,000 pps or less then you DON't need a step
> multiplier. As you can see you need to have all of the numbers to
> make an accurate prediction.