For me, LegTrax is the most interesting of the 3 Dai-X fighters, because it undergoes the most significant/obvious transformation in order to form part of the robot.
That might mean that it's the most challenging to do.
…
For my money, I don't see how the 'tracks' on Legtrax can actually be contained within the unit itself.
I can't remember whether you actually see the underside opening and the tracks extending down, during that fourth episode.
Yes yes yes. This! So much this!
When I was working on my first 3D model of Dai-X back in 2002 (!!!), I remember having to completely cheat to animate LegTrax. I had to dig deeeeeeeeeep into my file archives to find this, but I did remember trying to animate the transition as "realistically" as possible. I found it, and I just reuploaded it to YouTube here:

https://youtu.be/_nzG4jCIZ6k
What you don't see there, though, is that the
backs of the legs/shins on this model were
totally wide open and hollow. I also added a pair of sliding doors/panels in the inside of the lower legs to allow the hip part to slide into place. Also the feet have to move forward a bit to make space for the hips part that comes in behind them. But the actual "tracks"? Nope. Couldn't do it. I could not think of any way to reasonably fake that part into one single model.
I'm convinced that LegTrax simply breaks reality. It is impossible! A paradox! It's like… an inside-out TARDIS? It cannot exist in both forms without some kind of space-warping matter-rearranging wibbly-wobbly… maybe using lots of invisible nanites like Iron Man's suits in the later movies, the ones that could reconstruct themselves out of thin air like magic.
At a push, I wouldn't try to build it into the model, but I would have it as a further, additional little ship that gets delivered to Legtrax; a bit like the 'silhouette' equipment packs that get flown to Impulse Gundam in Gundam SEED Destiny.
You could even take that idea and run with it further, and give the track unit a more aerodynamic nose that breaks off and returns to X-Bomber, once the tracks unit reaches Legtrax.
Honestly, I think I'll probably just choose one of the two forms — probably the folded solo mode since that's how it normally resides when docked with X-Bomber — to build as a proper model. I might make a second joined/standing/robot version later, but they definitely won't have any connecting transformations.
