Battery¶

(battery/voltage) is the battery voltage in volts:

user=> (battery/voltage)
12.84

Every Control Hub and Expansion Hub measures the voltage it receives. With more than one hub, battery/voltage gives the lowest reading, because that hub is the first to suffer when the voltage sags. If no hub reports a voltage, it is 0.0.

A fully charged 12 V FTC battery reads about 13 V or more, and it drops under load, for example while the drivetrain accelerates.

Telemetry¶

user=> (telemetry/add-line (format "Battery %.1f V" (battery/voltage)))
nil

Voltage compensation¶

motor/set-power gives a fraction of the battery voltage, so the same power turns a motor more slowly on a tired battery. To get the same speed, scale the power by a reference voltage, here 12 V, over the voltage now:

(defn compensated [p]
  (clamp (* p (/ 12 (battery/voltage))) -1 1))

(motor/set-power "flywheel" (compensated 0.6))

At 12.84 V that gives 0.56, and at 10.5 V it gives 0.69. With an encoder, motor/set-velocity does this for you.