Re: Question on Mariss' E-Stop circuit

--- In CAD_CAM_EDM_DRO@yahoogroups.com, "Monte" <montejw@e...> wrote:

>
> --- In CAD_CAM_EDM_DRO@yahoogroups.com, "turbulatordude"
> <dave_mucha@y...> wrote:
>
> > The ohmage of the resistor is the result of a calculation, it is

not

> > a fixed value.
> >
> > That calculation is rather involved and quite frankly, the simple
> > version Mariss offered is not very complete.
> >
> > He proposes to dump 10 amps, and assumes 68 volts, ergo 68 volts
> > divided by 10 amps = 6.8 ohms. One would change both the

current

> > and the voltage for your power supply. there is no reason a 3

amp

> > power supply at 24 volts needs to dump 10 amps. Just as someone

with

> > a 30 amp 100 volt power supply would have to work with a whole
> > different set of values.
> >
> > Types of machines are also not included. rack and pinion and

belt

> > drive have the potential to have large pulleys, so a flywheel

effect

> > is very possible. An ACME screw will impart a considerable
> > resistance as opposed to a leadscrew.
>
> Okay, makes sense to me. Is there an 'easy' way to calculate the
> amperage needed to dump, or is it a measurement I need to make? 4
> axis Xylotex board, 2.5 amp/phase max, running at 2 amp/phase and

only

> 3 motors right now. Taig mill, 20 tpi lead screws, slow feeds and
> rapids, haven't measured the speeds.
>
> >
> > The whole dump circuit is a guideline, a starting point, not a

end-

> > all and be-all of e-stop circuits.
> >
> > Someone asked about a less abrupt power supply drain, then I

think

> > they said they will add a lighted indicator. Considder a simple
> > 110VAC light panel indicator. it is incandescent, has an

internal

> > resistance and will be lit from many DC power supplies.

Different

> > value bulbs are also available. But, that bulb will drain that

power

> > supply in short order when the power is turned off.
> >
> > Another concept not discussed is that 250 pound gantry on your

rack

> > and pinion plasma cutter shooting along a 400 ipm rapid, hitting

that

> > endswitch, and initiating that e-stop. if you unpower a stepper

or

> > servo, it freewheels. So, just what does that gantry do after

the

> > loss of power ?
>
> Make a lot of noise? I watched a mill with 2" ballscrews hit the

hard

> stop once. The operator was adjusting a new driver and it started
> occillating and blew right past all the limit switches to the end of
> the ballscrew
>
> Monte

Since the E-stop has been in the news so to speak, I think we should
get it over to the software guys.

Some people have dual end switches, a normal end switch and then a
second, e-stop to prevent a runaway axis from doing what you
mentioned.

But, that second should call for a software brake, not a total loss
of power.

Dave