I am new the hydraulic motion world, (13 years PLC controls background) and am working on a control upgrade project where we are considering using a Delta RMC200 in concert with a Controllogix PLC. The system is for testing vehicle drive axles and has 3 summation gearboxes (one on each corner of the axle) with 3 hydraulic motors on each gearbox for a total of 9 hydraulic motors. Each motor has swashplate angle feedback, and the ability to either motor or absorb depending on the swash plate angle command, so the system can either load or drive at every corner. One hydraulic motor on each gearbox has an quadrature encoder for speed feedback, and we measure shaft torque at the output of the gearbox. Depending on the torque capacity of the axle being tested, anywhere from 1 to all 3 hydraulic motors per gearbox (in any combination) are used. The system is fed by an 750HP HPU, and the outputs of the hydraulic motors feed back into the supply header.
My initial intention was to run each corner of the axle in Velocity/Force control to command speeds/loads on the axle, using a position axis then mirror the control output to the slave motors if they are being used. In an offline sample project, I attempted to create a control only output and push the master control output directly into the slave output using an expression, but the controller displayed an error stating the location could not be written to.
What would the best approach be with a system like this? Would there be benefit to running an inner control loop on swashplate angle for each hydraulic motor and have that tied into the outer loop running Velocity/Force?