Sudden Stop of a Servo Motor/Hydraulic Motor System

Seems to me Gone Coastal that since you already have the system in place why not experiment? I'm not to sure Solar Eagle's maths is going to help to much given they are standard issue formulae which seem unrelated to yr question - especially given there is not to much known about how much energy is in yr system at the point at which the brake's applied? My thoughts simply would be to apply the brake at different force x time (taken for the system energy to be absorbed by the brake) points and chart the torque spike - there must be a point where the brake energy = the system energy at a flat torque curve? be really interesting experiment! Have fun!

Well, without trying to reveal too much about the application because I'm not sure who may be prowling these boards, this system is currently at a contractors installation where they have been having trouble with it and I asked them to perform experiments just like you suggested. I wanted them to run some low speed low torque trials with the sudden stop and scan the data in the 10khz range to see what the effect is.

I'm having trouble getting them to perform this, which tells me they know what it will reveal and are trying to slip something past me or they don't think it's a problem which I'll have to demonstrate with the math first to coax them into trying the experiment.

If you apply a brake to any part of the system without shutting off flow to the hydraulic motor the hydraulic pressure will increase, increasing the torque output of the hydraulic motor until; the pressure relief valve on the hydraulic system opens, or shaft shears, or the brake burns out. Dangerous scenarios like burst pipes should be prevented by the pressure relief valve, but if I was locking the output shaft of a hydraulic motor I would stand well clear beacuse the pressure build up is very fast and things get unpredictable. Hydraulic motors can generate extremely high torques and shaft shearing is not uncommon. Shutting off hydraulic flow with a closed centre spool valve will create a braking effect and a torque spike will register in the shaft without the need for a brake and without creating a potentially dangerous situation.

I do not know if you will look again because I react quite late but I give you the answer. Your system in the assumption that you act the brake so fast that its torque could be considered as a step and that both motors are not any more supplied but running at full speed can be assimilated with 2 inertia (hydraulic motor and electric motor reduced on the hydraulic shaft by multiplying with the gear ratio ^2) and connected with a spring -the torque transducer.

The maximal torque which could appear is the maximal brake torque so that you MUST take care that this will not be > than the full torque transducer capacity considering -if the braking is frequent - a reduction safety coefficient for a fatigue reserve.

This is the worse case since if the torque grows over time in a continuous way the maximal torque will ALWAYS be less the one in case o a step braking.

If you want I can give you the equations and as an electric engineer you can deal with the Laplace transform used in control analysis.

If you apply the brake with both motors under load then the system of equations is different so that give the info (may be I misunderstood you OP).

Hope it will help.