Run a stepper from 2 DM542 drive

[BeagleBrainz]

Not intended to drag this conversation onwards, but for clarity on the behaviour of a stepper driver:

A stepper driver can be described as a finite-state machine. It will present a series of currents to each of the two (e.g.) coils according to the number of micro-steps selected. The following is an extract from the data sheet for the TB6600 - though the principle applies to any stepper driver.



You should be able to see that for a 1/8 micro-step, there's 32 discrete states for the A/B coil currents. Whether you move CW or CCW, you're just stepping either forwards or backwards in the state-machine ("phase", in my original post).

My point?, if using two stepper drivers, each will maintain it's own internal state as its operated. If you swap the outputs from one driver to another - unless there's the random fluke of each driver having the same state, there WILL be a discrete change in the coil currents appropriate to the different phase in the state machine that WILL result in a discrete change in shaft position. There's no mechanism available to synchronise the drivers. Disabling the drivers before switching the STEP/DIR will have no impact on this.

A_Camera's point of switching grounds is valid - or my lazy assumption that you share a common ground.

Very good points.

As long as the outputs driving the STEP & DIR are at a logic LOW (assuming common) is ground there should be an issue, but if the outputs are at a logic HI and using a mechanical switch to change over disabling the drive would prevent spurious steps, due to bounce.

All in all a better mechanical design would help.

Actually it would be worthwhile knowing the circuitry that drives the STEP & DIRECTION, before really delving in too deep. Considering that the design requires switching 2 different sources for driving the stepper who knows how the electrical side has been done.