Re: Bridgeport retrofit servo questions

Mariss,
In all of my research I haven't been able to get a consistent
reposonse regarding the original steppers and new drives. Some say
they use Geckos and they only get 50 IPM reliably, others use Larkens
others say they are getting 200 IPM rapids with stock steppers...So,
not to doubt anyone, but I just can't get a straight answer about
what really works reliably in this particular scenario and what
doesn't. I hear stories of poor low speed performance and drives
burning out left and right. I REALLY don't want to deal with that.

If I heard from a few people that were using a certain driver
reliably with good performance and few headaches, then I would
strongly consider it. Looking on various boards though, I get
conflicting stories regarding steppers and drivers on the BP.

Just about every retrofit 'kit' available for a Bridgeport is servo
powered. If steppers are cheaper and easier to setup, then why don't
they offer them in a retro kit?

-Brady

--- In CAD_CAM_EDM_DRO@yahoogroups.com, "Mariss Freimanis"
<mariss92705@y...> wrote:

>
> Brady,
>
> A lot of people have kept the motors and power supply on the

machine

> you mention and trashed the drives and controller. Using our drives
> and a good CNC program like mach2 they get 150 IPM and seem very
> happy.
>
> I don't know myself because I'm just a EE that designs stuff but I
> don't use any of the stuff I build. Kind of like a plumber whose

own

> sinks are stopped up or a contractor-builder whose own roof is

caving

> in.
>
> Mariss
>
>
>
>
> --- In CAD_CAM_EDM_DRO@yahoogroups.com, "braidmeister"
> <braidmeister@y...> wrote:
> >
> > Mariss,
> > Thanks for the detailed explaination...I actually do CNC routing
> and
> > CNC plasma cutting using steppers and a proprietary control. I
> > recently bought a BOSS 5 Bridgeport CNC...and I need to upgrade

the

> > controls to take advantage of the higher memory capabilities...I
> have
> > been getting into mold making and bought the BP to make metal
> molds.
> > My router loses steps if pushed too hard...and if I have a run of
> > several 3D carvings in hardwood, I can't push it, or I'll lose
> steps
> > (which really irks me) Eventually the router will be upgraded to
> > Mach2 with a hotter power supply and 201s or 210s. This machine

is

> my
> > bread and butter...so no upgrades on it right now.
> >
> > No handwheels on the BOSS and I've haven't run a Bridgeport or
> other
> > manual mill since high school...although I can remember the force
> > involved in spining handwheels and cranks. The NEMA 42 steppers

on

> > the BP are working, but I don't want to keep them if I am going

to

> be
> > dealing with positional loss as a result of sluggish performance.
> > Yeah...I can run the machine slowly. BUT why do so if I have the
> > option to close the loop and gain performance to boot? This is

the

> > main reason for investigating a servo system.
> >
> > I have no idea how much weight I will be pushing around with the
> BP.
> > I have picked out motors that are economical, similar in power

and

> > performance of 'real' servo motors that the expensive
> upgrade 'kits'
> > use, and generally what I 'think' will get the job done. For the
> time
> > being, I am just looking for a decent combination that will get

me

> > 120 IPM rapids and excellent repeatability.
> >
> > -Brady
> >
> > --- In CAD_CAM_EDM_DRO@yahoogroups.com, "Mariss Freimanis"
> > <mariss92705@y...> wrote:
> > >
> > > Brady,
> > >
> > > We build both sevo drives as well as step motor drives so I

have

> no
> > > particular bias towards either. I'm also working on a true
> stepper
> > > servo which should blur the line even further.
> > >
> > > You should approach this first entirely from a perspective of
> power
> > > (Watts) needed to do the job. The choice of stepper or servo
> falls
> > > out from the results.
> > >
> > > As a good rule, if 100W or less is sufficient to do what you
> > require,
> > > hands down, use a stepper. If 200W or more is needed, you have

to

> > use
> > > a servo. In between, either will do.
> > >
> > > How can you figure how much power you need? A couple of simple
> > > equations should handle it.
> > >
> > > 1) You know how many inches per minute (IPM) and how many

pounds

> of
> > > force you need at that speed. Easy; use the following:
> > >
> > > Watts = IPM * Lbs / 531
> > >
> > > 2) IPM is easy but you don't have clue how many Lbs of force is
> > > needed. I'm assuming here you are a machinist and have used
> manual
> > > machines. Your experience is necessary.
> > >
> > > a) What is the diameter of a handwheel for a machine of this

size?

> > >
> > > b) From your experience, how many pounds of force would you

apply

> > to
> > > the handcrank before you'd figure you are doing something wrong?
> > >
> > > Take the results of (b), multiply it by 16 to turn Lbs into
> ounces.
> > > Multiply the result by the radius in inches of the handcrank.
> Your
> > > result is in-oz of torque applied to the leadscrew.
> > >
> > > Multiply that by your needed IPM times the TPI (turns per inch)
> of
> > > your leadscrew (5 TPI for a Bridgeport). The result is screw

RPM.

> > >
> > > Multiply the screw RPM by the torque you need (in-oz,

calculated

> > > above) and divide the result by the magic number 1351. Your
> result
> > > pops up in Watts.
> > >
> > > Let's say your result is less than 200W (more than likely) but
> you
> > > still want a servo. Think about this:
> > >
> > > Servos are sexy, steppers are not. Just like Ferraris and

Toyota

> > > Corrolas. The thing a Ferrari owner never tells you about is

how

> > much
> > > maintanance his toy needs. Meanwhile the Toyota reliably plods
> > along.
> > >
> > > Steppers are diesels while servos are turbines. Steppers are

high

> > > torque, low RPM motors, servos are the opposite. I test about

100

> > > servo and stepper drives a day. Both are the same to me though
> > servos
> > > are sexier. Can't deny that.
> > >
> > > The maintanace and use thing. Servos have to run at 80% of

their

> no-
> > > load speed to deliver their rated power. 80% of no-load is very
> > often
> > > much higher than you want the screw to turn at. That means you
> have
> > > to use reduction gearing. A stepper meanwhile can drive the

screw

> > > direct (1:1).
> > >
> > > Servos are fence-pole stupid. They will work into an overload

and

> > > Kamakazi themselves into destruction (burn up in overload). A
> > stepper
> > > is smart enough to shed a load by stalling. Anything that

breaks

> on
> > a
> > > step drive stops the motor, anything that breaks on a servo

makes

> > it
> > > take-off full speed. Steppers are plug and play, servos must be
> > > tuned. Servos are expensive, steppers are cheap. Usually servos
> > need
> > > gearing, usually steppers don't. You see where I'm going with
> this.
> > >
> > > The aggrivation, care and feeding of a servo is feasable only

if

> > you
> > > need more than 200W mechanical if you are pragmatic. On the

other

> > > hand, there is nothing like the smooth, silky, silent and ghost-
> > like
> > > power of a servo if you are not.
> > >
> > > Your choice.
> > >
> > > Mariss
> > >
> > >
> > > --- In CAD_CAM_EDM_DRO@yahoogroups.com, "braidmeister"
> > > <braidmeister@y...> wrote:
> > > >
> > > > OK guys...I've been reading posts on here for the past few

days

> > > > regarding servo motors. After replacing a dead power

transistor

> > in
> > > my
> > > > BOSS 5 Bridgeport (just got it....Y axis DOA)...and spending
> way
> > > too
> > > > much time trying to interface to what appears to be a bad ERS
> > board
> > > > (via serial)...I am now heading towards doing a complete
> retrofit
> > > of
> > > > the controls using Mach2.
> > > >
> > > > I'm on the fence about whether to retain the working steppers
> and
> > > use
> > > > Larken stepper drives ($200 ea....up to 16A/ph) plus some

type

> of
> > > > appropriate power supply, Campbells breakout and Mach2. The
> down
> > > side
> > > > of this may be that the machine doesn't move as fast as the
> BOSS
> > > > control can move it...but this is based on feedback from
> several
> > > > Gecko users on a BP. I am not looking to break any speed
> > > > barriers...but 50 IPM rapids aren't going to cut it. I need
> > > something
> > > > that can handle running several hours at a time. I saved for

a

> > > while
> > > > to get the BOSS...now I have to scrape some $ together to do

a

> > > > conversion...just so I can run the thing. I really don't want
> to
> > do
> > > a
> > > > conversion twice (always time for that, right guys??!!)
> > > >
> > > > The other choice that I have is to go with servos. The BP is
> > > > definately well into the servo side of the servo/stepper

choice

> > > > threshold. Not partial to Gecko or Rutex as either will do
> > > (actually
> > > > I am because the Geckos are cheaper). I have read that

several

> of
> > > you
> > > > suggest using some of the treadmill-type motors available

from

> > > > surplus center. There are several DC dual shaft motors there
> with
> > > > pros and cons to each. I am curious as to what models would

be

> > best
> > > > for a BOSS machine. Here are a few that were mentioned...and

a

> > few
> > > > more that I picked out: (All listed can be found on this

page:

> > > > http://www.surpluscenter.com/sort.asp?
> > > > UID=2005012813411678&catname=electric&keyword=MBDD )
> > > >
> > > > 1. $30. 10-1573 ~ 5100RPM rear shaft long enough for encoder
> off
> > of
> > > > 10-1834. Rated at 1.5 HP & 110v. Does this have enough juice
> for
> > > the
> > > > BP @ 75v? Current not advertised other than 1.4A no load.
> > > >
> > > > 2. $22. 10-1783/10-1783-A 2.5 HP rating 6750 RPM 18.5A 130v

int

> > > duty,
> > > > 95v continuous. Back shaft only .25" long. Will have to

extend

> to
> > > use
> > > > any type of encoder. I am guessing that this would be a good
> > motor
> > > if
> > > > run @ 75v/18.5A (within Gecko specs)...only thing I question

is

> > the
> > > > RPM/belt reduction. What ratio do you think is best on the BP
> > with
> > > > this motor?
> > > >
> > > > 3. $80. 10-1906 2.0HP 130v/15A 3210RPM Continuous duty. Has
> good
> > > > shafts for driving and encoding. Shipping wt 24#s...starting

to

> > get
> > > > heavier. This seems like a good motor...the current rating
> tells
> > me
> > > > that it has some cookies and the RPM is half of the previous
> > > > one...helping to curb insane reduction ratios.
> > > >
> > > > 4. $90. 10-1723 1.5HP 111v/7.6A 3100RPM 2-4hr rated

continuous

> > > duty.
> > > > Looks like a good motor as well...but it is a pig. Ship wt @
> 30#
> > > and
> > > > 13" long...not liking that, but rotor inertia makes up for

the

> > > length.
> > > >
> > > > What do you think??? I think #3 so far might be a

winner...yes

> it
> > > is
> > > > more $ than 1 & 2, but it has a beefy shaft on it, long

enough

> in
> > > the
> > > > back for an encoder and the RPM isn't outlandish. I'd like

120

> > IPM
> > > > rapids and enough torque to mill at conservative speeds.
> > > >
> > > > Sorry post is so long...I like to be as detailed as I can.
> > > >
> > > > Thanks!!!
> > > > -Brady