Re: motor sizing vertical slide EDM

1) I'd take another look at the rate of direction reversal
(acel/decel). 5 * 700lbs implies 5G of acceleration; Newton's "equal
and opposite force" means your mechanism would get pounded with a
3,500 lb sledge-hammer on each reversal.

1a) 1G of acceleration is 32 ft/sec^2, 120 IPM is 0.1666 ft/sec so it
would take 0.0052 seconds to go from zero to 120 IPM and 0.0104
seconds to go from -120 IPM to +120 IPM.

1b) The distance travelled from zero to 120 IPM at 1G acceleration is
ft = a * t^2 / 2; plug in the #s and get:
32 * (.0052 sec)^2 / 2 = 0.000434 ft or 0.0052"

1c) At 5G the (1a) value is 0.001 sec and (1b) value is 0.001"

My question would be is this worth it? The 1G time and distance
numbers are pretty small; the sledge-hammer is "only" 700 lbs and
only 158 Watts are invested in it instead of 790 Watts.
--------------------------

2) An unloaded servomotor does pretty good to accelerate at 15,000
radians/sec^2. 3,000 RPM is 314 rad/sec so it should take 314/15,000
or about 0.021 seconds to accelerate from zero to 3,000 RPM. This
motor-bound value would limit your load acceleration to about 1/4 G
(0.0052 sec from (1a)/ 0.021 sec from (2)).

Please check my math; my head seems to be full of rocks today.:-)

Mariss

--- In CAD_CAM_EDM_DRO@yahoogroups.com, tomp-tag <tomp-tag@...> wrote:
>
> Brad,
>
> Could you help me with some motor sizing?
> ( Mariss, I'm using some calculation you posted long ago )
>
> The calculations I used to size my motor were:
> Watts = InchPerMin * Weight / 531
> Torque oz-in = 2.55 * Weight / TPI * efficiency
> RPM = IPM * TPI
>
>
> The mechanics:
> I have vertical slides that weigh near 700 pounds ( 300kg)
> and, since this is for an ZNC edm slide,
> the immediate reversals make the load seen by motor much
larger,
> I estimate 5x ( I've read it was RATED near 10X )
> so the 'weight' is now 3500 lbs ( 1500 kg )
> WEIGHT = 3000
>
> The system uses ground ballscrew(HiWin/Star)
> 0.2" or 5mm pitch,
> 1.25 to 1.5" dia.
> . Schneeberger roller bearings,
> gear ration to be determined, but Gates wide toothed belts
(0.8 to 1")
> TPI = 5
>
> I want to move them at 120 inches / minute ( 3 m / min)
> IPM = 120
>
> The Math:
> Watts = 800
> = InchPerMin * Weight / 531
> = 120 * 3500 / 531 = 790 W, say 800 W to 1 kW
> Watts = 800
>
> Torque oz-in = 2.55 * Weight / TPI * efficiency
> = 2.55 * 3500 / 5 * 0.9
> = 1983 oz-in
> TorqueNm = 14Nm ( 1983 oz-in * (7.062 * 10 ^-3 ) )
>
> RPM = IPM * TPI = 120 * 5
> = 600 rpm
>
> The Conclusion:
> so a belt drive ( like 1" wide GATES power belt ) with a 5:1
gear ratio
> would allow use of a 3000 rpm motor, and add torque,
> maybe reducing the Toque requirement to near the 3 Nm mark
> ( 600 * 5 = 3000rpm at 5:1 )
>
> This also keep the motor rpm up,
> out of the dead area area where the EDM spends most of it's
time,
> but keeps the acceleration and velocity available for when it
needs to be
> QUICK ( neccesary for EDM ).
>
> So, I'm thinking a 1Kw motor at 3000 rpm and >3Nm torque.
> This is WAY bigger than any system I've seen, so I'm asking for
opinions.
>
> If I use 5:1 gearing and wide belts, this make for a pretty big
pulley on the
> screw, but allows for that low speed toque, and uses the whole
range of motor
> rpm. The system should respond immediately to unit (bit) changes
from the DAC.
>
> I'm thinking Yaskawa, Panasonic, Fujitsu type drives
> ( motor/encoder/brake plus amplifier pkgs)
>
> Any thoughts?
>
> thanks,
> TomP
>