Crab Fader

The layout

      LEFT STICK                     RIGHT STICK
   ┌───────────────┐            ┌───────────────┐
   │      ▲        │            │      ▲        │
   │      ┃ CRAB   │            │      │ THR    │
   │      ┃ FADER  │            │      │        │
   │ ◄────╂────►   │            │ ◄────┼────►   │
   │ REAR STEER    │            │ FRONT STEER   │
   │      ┃        │            │      │        │
   │      ▼        │            │      ▼        │
   └───────────────┘            └───────────────┘
    ◄──► springs back            springs back
    ▲──▼ HOLDS · ratchet         everywhere

thin lines spring to center · thick line stays where you leave it

Front steering and throttle live on the right stick — both spring-centered, so letting go means straight and stopped. The left stick steers the rear: sideways is a normal spring-centered steering axis; the vertical axis is the radio's ratcheted throttle-style axis, repurposed as the crab fader. No mode switch anywhere — crab, counter-steer, and front-only are just places your thumbs happen to be.

The trick

  FADER          REAR AXLE HOME          THE TRUCK
                 (stick released)
   up ▲            ╲╲  +45%            ↗ crab-walks
      │
  mid ─            ││  straight        ↑ tracks true
      │
 down ▼            ╱╱  −45%            ↖ crab-walks

The fader sweeps the rear axle's home position; the stick steers dynamically around whatever home is set. At center, the truck drives like any 4WS rig with self-centering rear steer. Rolled up or down, the rear holds a standing crab angle — hands-free — while both steering axes keep working on top.

One honest physics note: because the channel clamps at ±100%, a cranked fader reaches same-direction full lock early and gives up equal opposite-direction authority. That's why the fader caps at 45% — the stick stays in charge.

Why it exists

Crawler drivers already knew both halves of this. Stick-radio 4WS folks run one stick per steering servo ("so you never change steering modes while driving"). And hold-position rear-steer fans point out that self-centering "could knock the tires off line" mid-placement — which is why rear-steer knobs and 3-position switches exist. But every prior setup picks one: dynamic spring-centered rear steer or a hold-position control.

The crab fader refuses the trade. On an off-camber traverse, roll a few clicks of rear axle into the hill and the tail stops walking downslope — no thumb held against a spring for the whole line, no mode to remember to exit. Roll it back to the center detent and the truck is stock again. Premium 4WS radios sell auto-centering rear knobs as their headline feature; this scheme gets that for free from a gimbal spring, then adds the layer they don't have.

Run it on your radio

Any EdgeTX stick radio with a ratcheted throttle-side axis can do this. The recipe (channel numbers from the reference build):

1. CH1 ← Ail (right stick ↔) — front steering, expo ≈25.
2. CH2 ← Ele (right stick ↕) — throttle, on the spring-centered side so release = stop. Disable the throttle warning (it watches the ratcheted axis, which isn't your throttle anymore).
3. CH3 ← Rud (left stick ↔) weight 100 — rear steering — plus a second additive line CH3 ← Thr (left stick ↕) weight 45. That second line is the crab fader.
4. Optional: CH4 ← Ail — an independent mirror of front steering for a scale cockpit steering-wheel servo, with its own direction and throw.
5. Habit: zero the fader before driving off — EdgeTX can't switch-warn an analog axis. (A logical switch + beep at center is a nice add.)

Or take the whole thing: the reference model is models/pocket/model06.yml (“Titan24”) in the pack — a RadioMaster Pocket + ER4 driving a Furitek Titan Buggy Ultimate 24.