# OpenSCAD body redesign: notes

`body.scad` rebuilds the body of `../fusion360/body-bottom/bottom v59.f3d`
(top + bottom plate, PCB, coxa servos; legs are placeholders).

## Source of truth

The `top` and `bottom` **solids** in `bottom v59.stp` (inside
`bottom v59.f3d_files.zip`). The `top.dxf` / `bottom.dxf` sketches in the
same zip are older and differ (front/back notch, side curve, one servo
pocket with an extra notch), so they are not used.

Coordinates: the plates are written in the original's top-view frame
(u, v) = (Fusion x, -Fusion z); `fusion_to_robot()` rotates that by -90°
into the robot frame of `robot/Config.h` (X = v forward, Y = -u left).
Fusion's up axis is Y; Fusion Y = 0 is the top face of the bottom plate,
which is also Z = 0 here.

`body.scad` slices were overlaid on the original solid edges at every
feature height (plate faces, standoff split, counterbore floor, nut wells,
PCB bosses, pivot bosses, battery bay): all match, apart from the fixes
below.

## What the original body is

- Two 3 mm plates, cavity 27 mm (Z 0..27, top plate Z 27..30).
- Outline: arm ends r 19.5 around each coxa axis, concave fillets r 15.5
  at the mid arms, quadratic curves at the sides and a notch front/back.
  Fully symmetric (the "asymmetry" seen earlier came from a stray line
  near (128, 8) in `bottom.dxf` and construction points at x = 100).
- Coxa axes (u, v): corners (±50, ±100), mid (±65, 0) = robot
  (±100, ±50) and (0, ±65), same as `Config.h`.
- Coxa servos (HS-485HB): ears rest on the top plate (Z 30), case hangs
  in a 41 × 21 pocket down to Z 2. Shaft 10 mm from the outer case end.
  Ear screw holes ⌀2.5, 48.25 × 10 mm. Corner servos turned 50°.
- Under each coxa axis a ⌀14 × 2 mm pivot boss on the bottom plate; the
  coxa bracket (`hinge1` above / `hinge2` below, leg parts) wraps the
  plate edge between the servo horn and this boss.
- 4 standoffs ⌀15 at (u, v) (±35, ±30), split at Z 13.5: M3 from the top
  in a ⌀7 counterbore (floor Z 17.5), 8 mm grip, M3 nut in a hex well
  from below (top of the well Z 9.5).
- PCB: long axis along the body, 4 bosses ⌀5 × 1 mm under the top plate
  on the PCB hole grid (35.78 × 78.96), ⌀2.5 holes (self-tapping M3?),
  ⌀5 × 1 mm recess on top. PCB top face at Z 26.
- Teensy cut-out 23.78 × 66.96, centred.
- Slide switch at the front: slot 8 × 16 (v 57..73), ⌀2 screw holes 19 mm
  apart, "ON"/"OFF" engraved 1 mm, readable from behind the robot.
- Battery bay on the bottom plate: rails 3 × 13.5 mm high at |u| 26.06..29.06
  (52.1 mm between them), from v -74.21 (open, rear) to 31.79, end stop at
  v 28.79..31.79.

## Bugs in the original, fixed here

- Left-front pivot boss at u = -50.894 instead of -50.
- Right-front corner has no coxa servo (only 5 of 6 placed).
- Only 2 of 6 legs (the mid legs), plus mirror-naming leftovers and the
  empty `dontdeleteme` component (nothing to port).
- Hex nut wells rotated randomly; now one orientation.

## Leg dimensions (for robot/Config.h and the Unity sim)

Measured on the original solids (left mid leg, `bottom-leg v31`):

| Item | Value | Config.h today |
|------|-------|----------------|
| Coxa: coxa axis to femur axis, horizontal | 55.0 mm | `COXA_LEN_MM` 55 (matches) |
| Femur: femur axis to knee axis | 100.0 mm | `FEMUR_LEN_MM` 100 (matches) |
| Tibia: knee axis to foot ball centre | 150.0 mm | `TIBIA_LEN_MM` 150 (matches) |
| Foot ball radius | 5.0 mm + 0.5 mm TPU sock wall (same on the real robot) | not modelled |
| Femur/knee axes height | in the coxa's joint plane, 13.5 mm above the bottom plate's top face | coxa pivot at Z 0 (matches if Z 0 = that plane) |
| Leg mounts (coxa axes) | (±100, ±50), (0, ±65) | matches |
| Original pose | femur 0°, tibia -90° (foot straight under the knee) | |

So the link lengths need no change. What the firmware and Unity don't know
yet: the ground contact is the foot ball's surface (5 mm + sock from the
point the IK places), and the body's underside (coxa bracket lower arm) is
21.5 mm below the joint plane.

## Physical limits

Collision sweep of the model's real parts (2D, per joint, in 0.25° steps;
cross-checked with full CGAL intersections of body and legs). Joint
convention as `robot/Config.h`.

| Joint | Range | Stopped by |
|-------|-------|-----------|
| Coxa, mid legs 1/4 | -66.5° .. 66.5° | coxa bracket shell hits the plate waist |
| Coxa, legs 0 (front-right) / 3 (rear-left) | -95.75° .. 66.75° (sideways mount: -35.75 .. 126.75) | same |
| Coxa, legs 2 (rear-right) / 5 (front-left) | -66.75° .. 95.75° (sideways mount: -126.75 .. 35.75) | same |
| Femur | -101.25° .. 101.25° | femur link hits the coxa bracket |
| Tibia | -177° .. 12.75° | rod folds into the femur link / tibia shell hits it |
| Servo travel | coxa/femur ±90°, tibia -180..0° | from the `SERVOS` pulse ranges |
| Leg width at the joints | 33.7 mm to the horn side + 21.5 mm to the bearing side | neighbours touch at 55.2 mm |

Hexagon layout (owner's request): corner legs mounted 60° round from the mid
legs (mount angles ±30 / ±90 / ±150); this needs the four corner coxa
brackets turned 60° on their servo splines. In the firmware (`Config.h`):
per-leg `COXA_MIN_DEG`/`COXA_MAX_DEG`, all ±60 now (the sideways layout
needed -32..60 / -60..32 at the corners),
femur ±80 and tibia -150..-20 unchanged (inside the physical range), and
`LEG_CLEARANCE_MM` 56 (was 30). `sim_smoke` passes; turning on the spot
runs at ~77°/s with legs at least 97 mm apart (sideways layout: ~29°/s).

## Unity simulation

`export_unity.py` renders the parts into
`Hexapod_Simulation_Unity/Assets/HexapodSim/Resources/OpenScadModel/*.bytes`
(rerun it after changing the SCAD files). `OpenScadModel.cs` hides the old
scene's robot and builds a new rig with the same names at the exact
Config.h geometry; `HexapodSimulation.useOpenScadModel` switches it off.
`Editor/OpenScadModelSnapshot.cs` renders it in batch mode for checks.

## Remote (`remote.scad`)

Rebuilt from `../fusion360/remote/remote v40.f3d` the same way (slices
match the original). Bugs fixed: the lid was off by (0.406, 0.21, -0.365)
mm (sat in the ledge, posts overlapping the bosses); the display bezel's
mesh facets became a clean window; the stray Body12 (an ON-OFF bracket
line never cut in) is left out. The display is a Nextion NX4832T035
(3.5" Basic); its board's M3 holes are the lid's 94.2 x 48.5 post grid.
Reference parts in `remote.scad`: the joysticks are JH-D400X-R4 (4-axis,
X/Y ±25°, twist ±45°, button; owner), mounted with the dust cover on the
lid's top face; their M2.5 square is 32.5 mm, so the lid's screw holes moved
from the original's 33 mm square to 32.5. The battery is an 18650 UPS/boost
board (89 x 22 mm, SMD-holder version, 22.4 mm tall; owner), on the bottom's
two d5 standoffs at (±27.9, -15) with the floor slots beside them for a
strap; its hole spacing (55.8 mm here) is not confirmed. No collisions.
Also from the owner: the bump on top of the middle post is a lanyard loop
(the original's tunnel through it is modelled); the square hole is the on/off
slide switch, mounted on top (same switch as the robot). Inside: an IMU on the
21 x 9 mm block (assumed GY-521), a USB-C breakout on the side-port block, and
a Teensy **4.0** (confirmed by the owner, although `platformio.ini` builds
the remote for a 4.1); it has no mounting holes and is placed on the
hole-less 8 x 24 mm block as a guess.
Open: what the 6 mm x 10 mm holes in the bottom bosses hold (magnets?), and
whether the upper two bosses are meant to be asymmetric (x -80.387 / +82.73).

## Notes for future designs

- Servo wires barely fit on the real robot: the six servo headers hang
  above the battery bay, and the front pair sits right over the bay's end
  stop (X 28.8..31.8, top at Z 13.5). Kept as-is for now; give the plugs and
  wires more room next time (e.g. a lower or shorter end stop, or a battery
  that leaves space under the headers).
- The nRF24 under the switch is fine on the real robot.

## Open questions

1. Front = switch end (inferred from the ON/OFF text orientation)?
2. PCB direction: `PCB_USB_FRONT` (Teensy USB, 7805 and LED at the front,
   nRF24 and battery JST at the rear) or reversed?
3. Battery size. The six servo headers hang above the bay (|Y| 14-15 mm)
   and the JP1/JP4 or JP3/JP6 pair touches the end stop; servo plugs and
   the battery need to share that space.
4. Leg geometry: in the original the femur servo sits further out than
   `COXA_LEN_MM` = 55 suggests. Check when porting the legs.