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

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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