Re: Bridgeport retrofit servo questions

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