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

Chris;

There is another factor that you must figure in, the force
of your pull on the line. That force adds to the motor's
torque and must be subtracted from your reading.

For example, if your reading it 10 pounds and your
hand is pulling 2 pounds then the force from the motor
is 8 pounds. Use the 8 pounds and the pulley diameter
to figure your torque.

Since you already have another scale use it measure the
amount of your pull. Using two scales, if they are accurate,
should give you a good reading.

Pete.

----- Original Message -----
From: "lcdpublishing" <lcdpublishing@...>
To: <CAD_CAM_EDM_DRO@yahoogroups.com>
Sent: Tuesday, May 16, 2006 4:31 PM
Subject: [CAD_CAM_EDM_DRO] 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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> OFF Topic POSTS: General Machining
> If you wish to post on unlimited OT subjects goto:
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> if you have trouble.
> http://www.metalworking.com/news_servers.html
>
> http://groups.yahoo.com/group/jobshophomeshop I consider this to be a
> sister site to the CCED group, as many of the same members are there, for
> OT subjects, that are not allowed on the CCED list.
>
> NOTICE: ALL POSTINGS TO THIS GROUP BECOME PUBLIC DOMAIN BY POSTING THEM.
> DON'T POST IF YOU CAN NOT ACCEPT THIS.....NO EXCEPTIONS........
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