🚀 Need Help Mimicking IDEX System in grblHAL Plugin (Dual Head Setup)

[samerjawadi]

Hey everyone! 👋

I'm working on a grblHAL plugin to mimic an IDEX-style dual-head system for 3D printing. The idea is to control two independent heads:

• H1: moves on X and Z axes
• H2: moves on A and B axes

Both heads share the Y axis.

🧩 The Challenge

I'm stuck on redirecting or mirroring the movement of the X axis to the A axis. For example, when H1 moves along X, I want H2 to follow along A with the same motion.

I’ve successfully written code for:

• STM32F7XX
• iMXRT1062 (Teensy 4.1)

But it doesn’t work on STM32F4XX, and I’m not sure why. I suspect it’s something related to how motion planning or axis mapping is handled in grblHAL on that architecture.

❓ What I Need

Has anyone:

• Managed to capture axis movement and redirect it to another axis in grblHAL?
• Found a way to sync virtual axes like X → A?
• Faced similar issues with STM32F4XX boards?

Any insight or push in the right direction would be super appreciated. 🙏 I’m happy to share my plugin for Teensy (filled with bugs for the moment but it copy the movment)
custom_idex.txt

Thanks in advance!

[terjeio]

Position is stored in three different locations, you likely may have to sync all of them to avoid issues.
gc_state.position - the position used by the parser, mm
pl.postion - the position used by the planner, steps. Sync with sys.position by calling plan_sync_position()
sys.position - current physical position, steps.

The macro sync_position() can be used to sync pl.postion and gc_state.position with sys.position.
IMO it may be best to change sys.position when you need to and then sync the others with that.

The issue with F4xx could be that settings are out of whack - A and B steps/mm were 0 for me when I tried your code, do not know why. $RST=* fixed it for me.