Center Of Gravity Of Material Handling Equipment

Are you sure it's c.o.g that you want to find ? As a static arrangement , the c.o.g. is within the 4 feet of the work bench , so straight -forward toppling is not possible . Perhaps you are after the dynamic effect when the motor starts (?) . Also , at a quick glance , thats a lot of weight to move into working position , and the 4 cross pieces look alarmingly small for the load .

If you enter correct mass/weight for each component, your 3D cad software will give you CG of the assembly.

Pineapple

if you extend the support legs that are on load side so that the load will be between the legs, then it should work even the equipment is lighter then the motor

This is correct, if possible.

Also, move the crank and gearing system to the other end of the scissor lift, with only a cable and lifting arm on the load side. The weight of the gears etc. will act as a counterweight with a relatively long lever arm.

To avoid a problem the vertical from the center of gravity of the whole system must cross the horizontal plane within the polygone of the contact points. In your case the rectangle. One should consider the weight variations and make the calculations with the extreme values and take a safety margin of at least 15%. In case of dynamic loads those have to be considered as well since they move the angle of resulting force which is no more vertical. An unstable situation could occur.

Sorry for the intrusion, but does any one else wonder about the stiffness of the arm that is picking up said 250 kg motor?

COG will be moot after arm/bracket bends into flaccid lifeless wilted curve.

From the sketch I'm really concerned.

milo