Hydraulic motor


Thread Starter

Arturo Arevalo

Hi gays, I have a hydraulic motor that I need to replace for a servomotor, I need to choose the capacity of the servo based on the following

54" TRAVEL @ 2.5 S.
4.6 G.P.M.

I don't know the meaning of these units and if they are useful to calculate the capacity of the servo.

I would appreciate your help.

Most servomotors when combined with a gearbox and a linear actuator can provide the necessay acceleration and movement. Most often the
information required is torque and RPM.
Also need to know what pressure you are running at to then get power. A more effective way is to know what force you need, how fast you need to go, and what is your actuation device (i.e. ballscrew, leadscrew, rack and pinion...) 54" in 2.5 sec is getting up there for a lead screw device. Accuracy can come into play-maybe you don't need a servo, just a standard drive. Email me some of these parameters (there will be more questions) and we can go from there.

[email protected]
1) either 14 cubic inches per revolution or 14 cubic inches per radian (probably revolution)

This is the amount of hydraulic fluid required to move the motor a given distance.

2) Moves 54 inches in 2.5 seconds.

3) 4.6 gallons of hydraulic fluid per minute.

The 54 inches in 2.5 seconds is the most useful
information. From it you can define a velocity
and acceleration profile, and with information
on the inertias, friction, and load can select
an appropriate motor and gearbox.

Steve Bailey

When you size your servo motor based on the hydraulic motor it's going to replace, you are assuming that the person who sized the hydraulic
motor made the proper choice.

What you should do is to calculate the motor you need based on the load you need to move, the acceleration/deceleration rates required, the
efficiency of the drive train, and the duty cyle. Most of the major motion control vendors have motor sizing software available to help you
choose the correct motor for the application.

Bob Peterson

This is really good advice. Another issue is that hydraulic motors seem to be a bit more forgiving when beat to death, or operated in hot conditions. If you use an electric motor of some sort to replace ti, the drive may just shut it self off on overload or excess heat conditions.

You may also find that a servo motor requires more physical space.

Coupling may be an issue too. I have seen some very strange coupling arrangements used with hydraulic motors.

You may also have to do some rethinking on what happens on power failure. The machine designer may have used characteristics of the motor itself as part of his design. These would no longer be applicable. You will also have
to accomodate what happens if the servo drive fails. This might require somemodifications to keep the machine safe.

It seems that hydraulic motors have largely gone out of style, so it could be
that the machine is a bit dated. If the machine is more than a "few" years
old, you may also have to do some substantial modifications to bring it up to
current safety standards.

Bob Peterson