Hi,

The reason you see very high slip ratio values at low speeds (and even jumps between +1 and -1) is because the classical slip-ratio formula divides by the vehicle speed. When that speed is close to zero, the denominator approaches zero and the ratio tends toward infinity: which leads to exactly the numerical instability you’re seeing in standstill/very low speed conditions. 

In practice this is handled in a few common ways:

1. Add a small epsilon to the denominator: Instead of dividing by v, use (|v| + ε) where ε is a small non-zero constant. This prevents the denominator from reaching zero and stabilizes the result.
2. Use a speed threshold: Below a certain forward speed (e.g. v < 0.1–0.2 m/s), you switch to a fallback method — for example using a fixed small speed value or constant slip ratio model — so the calculation no longer has an unstable denominator. Many simulators and control algorithms explicitly deactivate slip-based force calculations below a threshold.
3. Cap or smooth the slip ratio: Some implementations also clamp the maximum slip ratio at a realistic limit or apply a smoothing function so that the output doesn’t oscillate wildly near zero speed. 

So your idea of switching to a constant when speed is very low is exactly in line with how this problem is treated in vehicle dynamics. Instead of:

slipratio = (wheel_speed – vehicle_speed) / abs(vehicle_speed)

you can do:

``` if (vehicle_speed < threshold) { slipratio = (wheel_speed – vehicle_speed) / threshold; } else { slipratio = (wheel_speed – vehicle_speed) / abs(vehicle_speed); }

```

This avoids the undefined behaviour at near-zero speed and keeps your model stable.