So, in as much as progress, it's been a trickle rather than a flow, but a slow, and progressing trickle none the less. It is important to note, that I am entirely a hobbyist that incidentally is very interested in EE, design and gadgetry in general, hence the selection of ready to use boards, as opposed to some of the amazing but custom designs on here.

In as much as a final shape, I have settled in some sketches as to what the final design will be like. For Tortuga 1.0, I have decided I'm going to keep it as simple as possible, the final product will be cuboid in shape, the line dragging tool for the sand will be a simple linear actuator contained within the chassis. As for final hardware decisions, the following is a non-comprehensive list of the final hardware choices:

BOM:

1x ESP32-C6 Microcontroller

1x TB6612FNG Motor controller

1x DFR1026 Battery management system

1x USB C pigtail

1x 7.4V LiPO battery

4x N20 style motors

4x 685ZZ radial ball bearings

For now, the prototype will be USB tethered for control but ultimately, the final goal will be to either have external control from some kind of handheld controller, such as an XBOX controller or a mission planner, where the pattern is drawn in an app, with Tortuga translating these into cartesian co-ordinates. 

What next? Well, starting work on the drive system more than likely, although I had earlier mentioned a reluctance to examine the use of differential steering, this is most likely the optimal solution for the steering issue. After that some kind of low pressure, slick tyres to spread out the weight will need to be designed. Think along the lines of a Beach wheelchair. 

The physics behind a beach wheelchair is actually quite interesting, the force exerted by a vehicle is referred to as ground pressure, the measurable metric of ground pressure is potential mobility. Essentially, the greater the area and the lower the pressure, the easier it is for the vehicle to "float" across the surface. This is why hovercraft simply glide over most surfaces and unfortunately, is also the reason why we're unlikely to ever see a truly useful walking mecha, much to the chagrin of us Gundam enthusiasts. 

Ground pressure is relatively simple to work as far as equations go, simply put it is: P=F/A where F is the weight in newtons (N) and A is area in m². For sand, low pressures around the 1 to 2 pascals (12-14PSI) area are considered optimal. All this is aside as the pressures exerted by Tortuga are so small, it's almost not worth going to deep into it. None the less, this is an interesting delve in to the physics behind it. If you think this is bad, you should see me proselytise about the virtues of the BS 1363 plug AKA the British 3 pin plug.