SmartFuel¶
SmartFuel is a battery fuel gauge built for helicopters. A plain voltage-to-percent reading jumps around in flight: it drops on every collective pump as the pack sags, then climbs back when you unload. SmartFuel gives a percentage that only ever goes down, allows for sag under load, and can use consumed mAh as well.
It feeds the fuel reading everywhere: radio telemetry, the Lua suite dashboards and callouts, and the LED strip.
Setting it up¶
- Set up the battery voltage source -- and, for the Current and Combined modes, the current source -- on the Power tab. A voltage source is required: without one, SmartFuel turns itself off.
- Fill in the active battery profile: cell count (or 0 for automatic), capacity in mAh, and the Full and Min cell voltages. SmartFuel reads 100% at Full and 0% at Min.
-
Choose the Smart Fuel Mode:
Mode Uses Best for Voltage Pack voltage, with sag compensation in flight. No current sensor. Current The starting voltage, then mAh used against the pack's capacity. A well-calibrated current sensor. Combined Whichever of the two reads lower at the moment. The safest choice with a current sensor. -
Set the Smart Fuel Alert Level -- your landing reserve, default 35%. The radio scripts show 0% fuel at this level, so "empty" on the radio means "land now, with reserve left".
How it behaves¶
- When you plug in, SmartFuel takes its starting point from the pack voltage, once the cell count is known.
- From then on the reading can only stay the same or fall.
- In flight, it adds back the voltage sag it expects from your collective and cyclic load, so pumps and punch-outs don't make it plunge.
- If you plug in a pack that isn't full, it starts from the lower reading.
Tuning¶
Start with the defaults and fly. After a few flights, compare where SmartFuel is at landing with how much charge the pack really has left (what your charger puts back in). Change one thing at a time:
| What you see | Change |
|---|---|
| Drops sharply under hard load | Raise Sag Gain, or lower Charge Drop Rate |
| Too pessimistic in flight | Raise Sag Gain |
| Too optimistic in flight -- lands with less left than it says | Lower Sag Gain |
| Lags behind the real pack throughout the flight | Raise Voltage Drop Rate or Charge Drop Rate |
| Setting | Default | Range | Meaning |
|---|---|---|---|
| Voltage Drop Rate | 10 | 0-250 | How fast (mV per second, per cell) the voltage it works from may fall. |
| Charge Drop Rate | 50 | 0-250 | How fast the displayed percentage may fall once armed, in 0.01% per second (50 = 0.5% per second). |
| Sag Gain | 40 | 0-100 | Expected sag per cell at full stick load, in 0.01 V (40 = 0.40 V). |
These three only affect the voltage part. In Current mode with mAh coming in, the reading follows the mAh counter directly.
Without SmartFuel
With SmartFuel Off, the charge level is mAh-based if a capacity is set -- which reads 100% forever without a current sensor -- or a simple straight line between the min and max cell voltages otherwise.
See SmartFuel internals for the details of the algorithm.