Re: [CAD_CAM_EDM_DRO] Re: small servo motors keep stalling

feck123 wrote:

>--- thanks for the help and suggetstions with my motor problem....I am
>gonna try to get it goin next week with some tchnical assistance from the
>place i bought the setup from...He also wanted me to post an e-mail he
>sent to me with explanation of the torque ....here it is.......It is correct that
>The motor in question is a gearmotor with a 5.9 to one gear reduction.
>Approx free speed for the gearhead output shaft is around 1000 rpm.
>
>The CSP-1 description on the website references a 250Lb max thrust.
>Notice first that this is a maximum not a continuous value.
>That parameter should be asterisked. If you continue reading down the
>page, The footnote references that this number is achieved using a 5 TPI
>ballscrew .
>
>Let's do a little math. Kt= 5.17 ozin/A for that motor . Note the pwmamp-3
>can continuously output 3A with 6A peak current capability.
>
>Pre gearhead Torque = 5.17 x 3= 15.51 ozin (before the gear head)
>
>Now lets multiply that number by the gear ratio to get the torque at the
>output
>shaft and don't forget the gearhead efficiency
>
>Constant torque= 15.51 X 5.9 x (.95 )= 86.93 ozin
>
>
>A ballscrew with a .200" lead ( 5tpi) generates about 1.765 pounds of
>thrust
>for every ozin of torque applied
>
>So my continuous thrust at ( 3 Amps ) is
>
>Thrust = 86.93 x 1.765 = 153 Lbs
>
>If I push the amp for a short interval to it's peak current rating of 6A I could
>generate
>
>300 lbs of thrust. Notice this peak is well above the maximum thrust called
>out in our literature.
>
>

BUT!!! This is assuming 100% efficiency of the screw. Ballscrews
approach this
efficiency, but a 60 degree thread form is MUCH worse, something like
10% under
load. So, in this case, the table really gets more like 30 Lbs of real
linear force, the
rest is burned up in the screw. (Yes, note, the servo system maker
recommends
ballscrews, this user didn't use them.)

>This level of thrust on a small machine is more than adequate for most
>applications.
>I am referring here to Jon's comment that the system is under powered
>even with a ballscrew.
>
>On the issue of backlash. There is backlash compensation in the
>software for any or all axes. With the above motor there is typically about
>0.001 " lash when using a
>0.200" lead ballscrew.
>
>It amazes me that a person with no experience with this system ( Jon ) is
>so quick to
>malign it in a public forum.
>

But, the user is NOT using a ballscrew. These are really inportant, but
this servo system
just doesn't have the torque to run high-loss screws.

> We have sold many of these systems as well as
>machines based on these motors and amps since 1996. Many of these
>systems
>run 8 hours a day, day in day out .
>
>

But, your customer's system is NOT working, at all.

Jon