Sunday, December 7, 2008

Balance of Forces/Cylinder

A cylinder will travel at a constant velocity from 0-100% as long as the forces on both sides of the piston, the load force, and any other forces such as friction are in balance. When the forces are not in balance the piston and rod will accelerate (positively or negatively) until the forces are once again in balance.


pnachtwey said...

The VCCM equation for calculating the actuator speed is based on this concept. People that base their speed calculations on V=Q/A or the "flow makes it go" equation assume the actuator is already moving and speed V. This assumption is often incorrect since the load can't instantly accelerate to speed V nor can one assume there will be enough force accelerate to speed V in the length of the cylinder. It is also absurd to believe one can can infinite speed by making A very small. Newton didn't include flow in his 3 laws of motion.

JDK said...

Sorry to sound stupid. Do you agree with what I said?

pnachtwey said...

Yes. The VCCM equation is derived from the balance of forces concept. The VCCM equation provides the true maximum steady state velocity. Vss

Those that use the "flow makes it go" equation, V=Q/A, to calculate maximum steady state speeds don't account for opposing forces.

JDK said...

I agree, if you assume only a flow (Q) and don't consider pressure requirements due to forces such as load, friction, flow resistances, etc., your calculations will not be correct.

lilu said...

if it is hydraulic motor , what is the vccm equation after balancing of torque involved in th system .

JDK said...


I have been away.
I would assume that you substitute 1 into the equation for Pc since Ape = Are