Re: Force through ball screw based on stepper motor torque??

Chris,

I agree. There is a lot of difference in the spring scales I've
compared, too.

So I use a five gallon bucket with water as the weight. Precise,
clean, repeatable. You just add a bend pulley to Dan's setup and the
bucket does its thing.

I did use a bucket to Re-calibrate a spring scale I bought at HF.
Pretty blue aluminum thing. Now it's as accurate as the bucket...

Might work for your "three musketeers" as well?

Hope this helps,

Ballendo

--- In CAD_CAM_EDM_DRO@yahoogroups.com, "lcdpublishing"
<lcdpublishing@...> wrote:

>
> Hi Dan,
>
> Thanks much for the info. I actually had this type of setup about

2

> years ago - using fishing scales. I bought one, didn't get the
> results I thought I should. So, I went to another store, bought
> another scale and got different results. So, back to another

store

> and ended up with a third scale that gave me yet different

results.

> So, even though I don't fish, I have 3 fishing scales that each

give

> different readings (by several pounds).
>
> This is why I was going to use the "bucket" and weights method - I
> figured that I could get more accuracy that way. If you know of

an

> accurate brand of spring scale, that would be great, I will try to
> pick one up before i get back to bench testing and such.
>
> Chris
>
>
> --- In CAD_CAM_EDM_DRO@yahoogroups.com, "Dan Mauch" <dmauch@>
> wrote:
> >
> > Here is a better method for measuring running torque than the
> bucket.
> > Machine a pulley with flanges to about 2.375 OD. Then machine in
> between the
> > flanges down to 2.000" and machiene the bore to fit your motor
> ehich is
> > probably .2495".
> > You should have a hub so you can install a 8/32 set screw to

lock

> the pulley
> > to the motor.
> > Install the pulley on the motor that is secured to a base.
> Deadhead one end
> > of a heavy nylon cord ( tie one end to a fixed unmoveable)

object

> inline
> > with the pulley. The wrap about 3 turns around the grovoved
> pulley. Attach
> > the free end to a spring scale. Your step motor is probably 200
> steps per
> > rev so run the motor at the equivalent of 10 RPM i.e. 2000 steps
> per minute.
> > Pull on the spring scale this will stop the nylon cord from
> completely
> > slipping ( capstan) until the motor starts missing steps. This

is

> your
> > running torque at that RPM. run it at several other speeds
> recording the
> > torque. As long as the cord is slack it will slip as as soon as
> you pull on
> > the spring it will impart a torque of the pull of the spring

scale

> times the
> > radius . So a 5lb pull at 1"=5lb in torque which you can then
> convert to oz
> > inches.
> >
> >
> >
> > Dan Mauch
> > low cost stepper and servo motors.
> > cases for Gecko drives
> > kits and assembled 3-4 axis drives
> > www.camtronics-cnc.com
> > www.seanet.com/~dmauch
> > ----- Original Message -----
> > From: "lcdpublishing" <lcdpublishing@>
> > To: <CAD_CAM_EDM_DRO@yahoogroups.com>
> > Sent: Tuesday, May 16, 2006 12:55 PM
> > Subject: [CAD_CAM_EDM_DRO] Re: Force through ball screw based on
> stepper
> > motor torque??
> >
> >
> > > Update...
> > >
> > > Someone sent me an email reporting that they fried a drive by
> doing
> > > the current measurement as prescribed earlier. As I don't

have a

> > > backup drive on hand, I can't do the current measurement yet

(in

> > > case I blow something). I simply can't take the chance at this
> > > time, in about a month I will have some open time to

experiment.

> > >
> > > Answers to questions that have come back at me..
> > >
> > > This is the test setup...
> > >
> > > Bathroom scale against a fixed point - "padded" with a large
> block
> > > of wood to distribute the forces.
> > >
> > > Slowly, (as slow as I can jog), move the axis into the scale
> while
> > > reading the "force". I jog until the stepper skips - this is
> what I
> > > call the maximum force I am getting.
> > >
> > > This is done on all three axes with similar results. They do
> vary
> > > as not all three motors are the same.
> > >
> > > I do not have a means of measuring the torque of the motor
> directly -
> > > yet. I do plan on making a 2" diameter pulley with string and
> > > a "bucket" to load up with weight and measure it that way too.
> > >
> > > I don't have a motor dyno at my disposal so I am forced to go
> down
> > > the "Crude" measurement path :-)
> > >
> > > Chris
> > >
> > >
> > >
> > >
> > >
> > >
> > >
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