In addition to working with LinuxCNC I also help look after a 1916 fire engine. This fire engine has a 9 litre 4-cylinder engine with a large flywheel. A consequence of this is that on some hills that it could easily climb in third gear you can't get out of first gear if forced to come to a halt and re-start. The reason for this is the crash gearbox. To engage second gear you need to de-clutch and then engage the gear once the engine revs have fallen to match output-shaft revs. And up a hill the vehicle slows faster than the engine, so that by the time you could engage second, you need to stop and go back to first.
My lathe has a 2-speed gearbox, operated by electromagnetic clutches. It chooses the gear when the spindle is turned on based on commanded speed. This can be a bit sub-optimal when turning a large diameter down to a small diameter, as it ends up with too low a surface speed if stuck in low gear from the beginning. I have long had the idea of doing on-the-fly gearchanges: Wait for a G0, de-assert spindle-at-speed, disengage the current gear, synchronise the motor to the current spindle speed in the new gear, then engage the new gear. Today I did this, and I have the same issue as the fire engine. When switching from high to low gear it works very smoothly. The spiindle is disengaged and starts to slow, the motor accelerates, they meet in the middle, engage the gear and then ramp back up to the new speed. It works less well going from low to high gear, the spindle slows faster than the motor, so the spindle has stopped before synch happens. Just like the fire engine. It's still an improvement, but not what I was hoping for. I could probably make it work better by programming an active slow-down to the motor with a faster ramp. But to do that I need to drag the lathe away from the wall, as the VFD front panel is only accessible from the back of the lathe. (unless there is a way to program the VFD parameters via the modbus link) -- atp "A motorcycle is a bicycle with a pandemonium attachment and is designed for the especial use of mechanical geniuses, daredevils and lunatics." — George Fitch, Atlanta Constitution Newspaper, 1912 _______________________________________________ Emc-users mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/emc-users
