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

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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