Body genome

All genes are normalised to [0, 1] and mapped linearly onto their physical range on decode, so one mutation sigma works for every gene.

Module tree (darwinbot/morphology.py)

A tree of modules: core, joint, segment, link, spring, wheel, foot, tail, skid, spike and caster. Joints, segments (a spine servo followed by a second torso plate, at most MAX_SEGMENTS = 2, attached only to the front or back slot of the core or of another segment) and wheels carry an STS3215 servo; links, springs, tails, skids, spikes, casters and feet are passive. The genome is a fixed vector of MORPH_LENGTH = MAX_NODES * 15 = 300 genes: one block of 15 genes per node slot, with MAX_NODES = 20. Block 0 is always the core; the block index is the stable slot id of the node. A block is

Gene	Meaning
active	the module exists when > 0.5
parent	slot id of the parent module
slot	attachment slot on the parent (core: 12 slots, 8 on the contour (front, back, three on each side) and 4 on the flat faces (top front, top rear, bottom front, bottom rear); segment: 8 slots like the core; joint, link and spring: tip and two sides)
rot	roll of the attachment around the slot direction, any angle in [0, 2*pi)
type	joint, link, spring, wheel, foot, tail, skid, spike, caster or segment
axis	joint turns about pitch, yaw or roll; for a foot, the shape (sphere, blade, pad or claw)
length	link length 40 - 200 mm (tail: bar length)
wheel	wheel or caster radius (wheel 30 - 60 mm, caster 15 - 35 mm), or foot radius 8 - 30 mm; for a tail, the counterweight 0 - 100 g
flip	joint axis reversed (how a mirrored copy keeps the same signal)
width	link section width 12 - 30 mm
thick	link section thickness 3 - 10 mm; for a spring, the TPU blade 2 - 8 mm
offset	on the core: mount position along the torso edge (on a top or bottom face, across the torso); on a link side slot: elbow distance 25 - 80 mm
angle	on the core: mount yaw up to +/-60 degrees (on a face, yaw about the vertical, +/-180); on a link side slot: elbow angle 30 - 150 degrees
profile	link, joint or spring path: straight, L (two pieces) or arc (three pieces); ignored by other modules
bend	signed bend of an L or arc profile, -90 to +90 degrees

Passive module physics: a spring is a hinge whose stiffness follows from the TPU blade thickness (see "Mola de TPU" in hardware-dados.md); a tail is a bar with a counterweight at the tip; a skid has low friction (0.15), a spike high friction (1.6); a caster is a free wheel on a passive hinge. None has a servo.

For the core block, length and wheel hold the torso length (0.15 - 0.40 m) and width (0.10 - 0.25 m), and the unused genes hold the contour factors (0.4 to 1.4) of the 8 vertices of the star-shaped torso polygon, one per contour slot. For a segment, length and width set the plate (80 - 220 mm each). decode() accepts any vector and always returns a body within MAX_NODES, MAX_SERVOS = 16 and depth 5: blocks that are inactive, unreachable, clash on a slot or break a limit are dropped. A joint or link with no child ends in an implicit foot.

Mutation works on the decoded tree, one to three operators per child: nudge a continuous measure (one step in five is a large jump; this includes the torso contour, link profile and bend, and foot shape), stretch or shrink a whole limb, change a module type (including into a passive kind), add a module or small subtree, remove a subtree, duplicate a subtree mirrored on the opposite slot, or copy it to another free slot. One child in five is instead a graft: a whole limb of a second elite is attached to a free slot of the parent, mirrored when the opposite torso side is free, the crossover Sims (1994) used for his creatures. One body in ten in every batch is drawn from scratch rather than bred (random_frac in evolve.run). The initial population mixes small random trees with seeds that reproduce mirrored leg pairs, with and without wheels.