Friday, 15 January 2010

Initial tests complete

Having completed some initial test of the FACU PID control box, its time to strip the coxa down and make some changes to the design. This is to facilitate better hose movement through the coxa section, including three rollers to guide the hoses. Also we are going to change the encoder mounting design, which will bring the encoder at least 20mm closer to the body, keeping it out of harms way.

I am experiencing some issues with the position control of the rams. First off, having bled the system it seems that the Femur and Tibia are gathering air in the rams, even after running the system for some time the air does not disappear, its as if the air is being sucked in, yet we have no oil leaks? The next issue is that the rams which are not under load, such as the coxa while it swings freely on the coxa pivot, are very difficult to tune, I think this is due to the momentum of the leg and slight play in the mechanism causing an error on the encoder, which in turn is translated back through the system as a correction on the cylinder, this then causes oscillation. In order to tune this oscillation out, the drive has to be reduced to a value that is undesirable for normal use. We have a plan to pre laod the leg with a spring or gas strut, this may help.

Josh makes the first adjustment to the coxa.. with an alligator saw!!