How experimental speed control works¶

Experimental speed control silences Mazda's radar and sends its messages to control acceleration and braking. You set speed and engage with the steering-wheel buttons.

which cars¶

It needs a compatible Mazda EPS (2022+), factory-fitted or swapped, and the 2022 family's radar or the older G46L (the CX-5 2012–16 and CX-9 2016–20 qualify only with a G46L). The setting appears only when both match. It heads the Cruise panel, with Experimental Mode and its assists below it: Settings → Cruise → Alpha Longitudinal (comma 4: Settings → Cruise → alpha longitudinal). It changes only while offroad (car off, or Force Offroad) and applies at the next start. I tuned every value here on a 2022 CX-5.

taking over the radar¶

• Drove off first: it takes over at the next stop. SET shows Park to Engage Longitudinal.
• The car's own cruise is on: SET shows Turn Off Stock Cruise.
• The radar refuses, or does not answer in 10 s: it keeps control for the drive. SET shows Longitudinal Initializing Failed: Restart the car to retry.
• The radar speaks again later: zoompilot steps back at once with a cruise fault and retries at the next stop.

the camera start-up wait¶

After it boots, the front camera checks that the radar is there. If the radar goes quiet during that check, the camera latches an i-ACTIVSENSE fault that only a long power-down clears. So zoompilot waits for the camera's "boot finished" signal, then 7 s more. A camera error, or a gap over 1.5 s in its messages, restarts the count.

handing the radar back¶

Every software stop hands the radar back first, moving or stopped. A radar left to recover alone comes back degraded and blocks cruise until the next ignition.

• Force Offroad (Settings → Device → Enable Always Offroad): disengage first. A failed hand-back stays pending, with the camera kept fed, until you exit.
• Reboot or power off: goes ahead on any answer, or after 15 s.
• Ignition off: the radar recovers on its own.
• Turning it off while driving: Force Offroad, switch off, exit. The car's cruise is back.

stop-and-go¶

• Stop: openpilot holds with 1.024 m/s², the car's own value, until the car's brake hold takes over a few seconds later. If it never does, zoompilot keeps braking.
• Pull away: once the plan asks for over 0.25 m/s² for 0.2 s, zoompilot sends the car's release signal and ramps up at 1.25 m/s³. If still stopped, it climbs for up to 3 s, never past 1.45 m/s².

acceleration like the car's own cruise¶

• Build: at most 0.8 m/s³ above 13 mph (22 km/h).
• Lift-off: throttle eases off at most 2.0 m/s³ near your speed. Braking skips this.
• Ceiling: 1.75 m/s² at 9 mph (14 km/h), 1.05 at 31 mph (50 km/h), 0.65 from 56 mph (90 km/h). The panda enforces +2.0 / −3.5 m/s².

radar readouts¶

With the car's own cruise, openpilot combines up to 4 radar tracks with the camera. With experimental speed control every lead is camera-only. Cars whose radar sends no tracks (G46L, CX-5 2012–16, CX-9 2016–20) are camera-only either way.

lead cars¶

Instead of assuming a braking car soon stops braking, zoompilot uses the driving model's forecast of its speed, so braking starts earlier behind a slowing car, not harder. It is always on. If the model's car is over 4 m from the tracked car, openpilot's own estimate takes over. A car under 7 mph (11 km/h) is never assumed to pull away.

zoompilot also does the radar's other jobs: it reports the lead to the camera, lights the dash distance bars, and passes on auto high beams.

buttons, brake and gas¶

• MAIN: turns cruise on and off as usual.
• CANCEL or brake: the car cancels and openpilot follows. If openpilot drops out first, it waits 0.2 s before pressing CANCEL, because a second cancel turns cruise main off.
• Gas: overrides without disengaging, and releases a stop hold at once. You never need RES.

Speed-Limit Assist and Slow for Curves¶

• Slow for Curves: the planner slows the car itself. The dash set speed does not step down (details).
• Speed-Limit Assist: in Assist mode, ICBM still moves the dash set speed to the limit (details).