Talk:120 Toolchanger/@comment-99.247.248.209-20130819002206

The relay approach has the following problems:

-Mach can never be sure the toolchange is actually finished -- it waits a fixed delay time, crosses its fingers, and continues executing.

-the reverse voltage that safely limits stall current is insufficient to reverse the motor -- you either slow the toolchange dramatically or overcurrent the motor (likely both)

-because you rely on fixed delay times with safety margins, and probably reverse the motor slower than you need to, toolchanges take much more time than they need to.

In other words, every toolchange takes too long, you have no guarantee that the tool is ever locked against the pawl before you resume, and your motor life is shortened. These are big flaws that I didn't find acceptable even for hobby use, and I don't think you'd find any of them in any real commercial system.

The toolchanger controller is better because it continuously senses the motor current. This allows it to reverse the motor against the pawl at full speed, but immediately detect the motor loading up as it touches the pawl. It instantly switches to chopping mode to deliver a constant motor torque against the pawl, and simultaneously messages Mach that the turret is definitely against the pawl (not just in the right position, but also locked in place with correct reverse torque) all of which happens in a fraction of a second.

The motor never sees unsafe current when stalled, Mach always pauses for exactly the length of the toolchange -- never longer, and if the toolchange doesn't complete (with current showing the turret properly against the pawl with the set torque applied), Mach execution never resumes. This closely matches the original Emco system in function and is the minimum I'd consider acceptable for my machine, even for hobby use.