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

--- In CAD_CAM_EDM_DRO@yahoogroups.com, R Rogers <rogersmach@y...>
wrote:

>
>
> turbulatordude <davemucha@j...> 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

>