Re: [CAD_CAM_EDM_DRO] Re: Servomotors & Minimill - do these need speed reduction or not?

Larry Wright <lnw32@...> wrote:

I believe "hobby" implies that we don't want to pay
big dollars for the best products and that its about
learning.

Makes sense, I was just curious and thats the reason I asked the original question.

I have a EET background and I realize that for the
money servos are more efficient, but servo are also
more complicated and expensive. If someone can't get a
stepper to work then you don't understand what makes
the servo work. Recently I purchased a 4 axis kit with
4 steppers and the driver board for $150. Its not the
fastest and it won't run a mill

If you are just interested in theory of motion control I can understand this. My interest in CNC control is aimed at the end result of having a reliable, servicable machine tool.



but I can't imagine
buying servo motors, encoders and drivers for any ware
near this price.

Honestly, I know servos are far better to use. If
anybody knows where I can get a small servo package or
individual components for anything close to this price
I would love to know about it.

Larry Wright



--- turbulatordude wrote:

> --- In CAD_CAM_EDM_DRO@yahoogroups.com, R Rogers
>
> wrote:
> >
> >
> > turbulatordude wrote:
> > --- In CAD_CAM_EDM_DRO@yahoogroups.com, R Rogers
> > wrote:
> > > The low rapid rate and general lack of torque at
> high speed seems
> > to be the case with steppers. I'm wondering why
> anyone would opt to
> > use them. The drives are much more expensive, alot
> more difficult
> to
> > configure. Heating problems compared to servos
> etc. I've just
> noticed
> > alot of posts with questions regarding steppers
> and I'm just
> confused
> > why anyone would use them. There seems to be an
> abundance of used
> > servos around. One person one here mentioned that
> "the steppers on
> > his small mini-lathe produced enough heat to fry
> eggs"
> > >
> > > Ron
> >
> >
> > Becasue steppers are so dang easy to use.
> >
> > :::::They are? They weren't easy for me.
>
> the parallel port and 4 MOSFET's and you can drive a
> stepper. it
> don't get much easier than that.
>
>
>
>
> >
> > Also, because most people do not know where the
> 'abundance or
> > servo's' are
> >
> > ::::::Ebay, and from what I understand you can use
> any DC brushed
> motor as a servo by simply adding an encoder. i.e.
> small automotive
> or lawnmower starter motor used, very cheap. Silicon
> Salvage has tons
> of them. Google "standard DC motor as servo"
>
> I have watched the question on here more than once
> about what to look
> for in a DC motor to use it as a servo and it has
> gone unanswered.
> The volume of knoledge of steppers is either greater
> or simplier than
> for servos.
>
> Also, remember that there are guys who don't know
> the difference
> between a current liming resistor, or a pull up
> resistor or a sense
> resistor. (there is none, the name only defines the
> application)
>
>
> >
> > and/or don't want to get involved with encoders as
> there
> > are not a lot of cheap encoders around.
> >
> > :::::US digital under 40 bucks a piece
>
> $20.00 stepper plus $20.00 driver = $ 40 per axis.
>
> Cheap servo + $ 40.00 encoder + $100.00 driver = 3
> axis of steppers
> including power supply.
>
>
>
> >
> > Steppers offer the power at cutting speeds so in
> that way, are
> ideal
> > for home-brew.
> >
> > ::::::And no torque for rapiding. When I asked
> Microkinetics about
> driving the knee for Z on my Bridgeport with their
> stepper they never
> would give me a straight answer. Someone suggested
> gas springs to
> assist the knee, I guess they thought I was
> retrofitting a toyota
> hatchback.
>
> Who cares about rapids on a 12 x 12 pcb drilling
> machine ? or a 24 x
> 36 foam cutter ? Knee mills are only a small part
> of the CNC world.
>
>
> > Stepper drivers are easy to make, find or buy.
> >
> > ::::::My understanding is that "Chopper drives"
> are very complex
> and L/R drives dont work for machine tools. DC servo
> drives are much
> simpler by comparison. And cheaper
> >
> > There are a few complete stepper packages for
> small machines that
> > sell for under $200.00
> >
> > :::::I guess alot of it depends what you are
> expecting from your
> retrofit, size and how much it will be used
> >
> > I don't know of any servo packages that are that
> low cost.
>
> yup. I'm working on a PCB drilling machine. 3
> steppers, plus a
> breakout board, plus 3 drivers (single step) and
> power supply and I'm
> expecting it to be under $150.00 for all three axes.
> The low cost
> steppers are hard to find. but should be $10-15
> each.
>
> If there was a way to use servo's for the same
> price, I'd be all over
> it !
>
>
> Dave
> >
>
>
>
>
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