Marsen Energy 10Ah Parrot Disco.

• Capacity: 10Ah/10000mAh
• Nominal Voltage: 36V
• Discharge current: 30 Amps
• Standard Charge: 2 Amps
• Fast Charge: 4 Amps
• Charge Voltage: 12.6V
• Weight: 460g
• Dimensions: 375mm x 140mm x 19mm

How the Disco measures battery level

Many RC flight controllers with battery monitoring use a current sensor to measure how much energy is removed from the battery.

The Disco has no current sensor. Instead it monitors the battery voltage under load to figure out how much is left. This method has the advantage of the Disco not needing to know how large the battery is or how fully charged it was, to figure out how many percent capacity is left. The method has the disadvantage that it cannot know how much actual capacity is left, only how many percent.

When the motor runs on full power, the battery voltage temporarily drops. When the motor power is reduced, the battery voltage recovers. This is normal, and more pronounced in li-ion batteries than li-po. It means the battery voltage goes up and down all the time, depending on how much power you use.

To prevent the battery percentage display going up and down all the time, The Disco firmware only shows the lowest value it has measured. Any subsequent voltage recovery will not be shown. This can have unintuitive effects.

If you for example climb very high at the beginning of a flight, your battery level may drop rather quickly. Once you reach your altitude and start cruising, the battery level shown will stop falling and will remain on the lowest level you reached. It can be “stuck” there for quite some time.

This “battery level stuck” effect can also be seen with cold batteries. Cold batteries drop their voltage under load more than warm batteries, due to increased internal resistance. But batteries under load warm up, causing the battery voltage to in some cases actually rise with increased use! This too will result in the Disco user interface showing the battery level being stuck on the same value for longer than expected.

Software configuration for custom batteries

When using a li-ion battery pack, you don’t have to change any parameters. But if you don’t, the Disco will think you are still using a lipo and not use the whole capacity of your battery.

To use all of your capacity and to get proper % remaining reading with these packs, you need to change the voltage table the Disco uses to calculate battery state.

Configuration parameters

Here are the parameters related to battery voltage you need to change. First is a list of voltage levels for various warnings and limits.

# BATTERY
BATTERY_FILTER_CO_HZ = 1.0
VBAT_MIN = 8.8
VBAT_LOW = 8.9
VBAT_SHUTDOWN = 8.3

#/////////////////////////////////////////////////////////////
# PREFLIGHT
PREFLIGHT_BATTERY_LOW_LEVEL = 10
#/////////////////////////////////////////////////////////////

# SAFETY
SAFETY_GROUND_PROXIMITY_CHECK_ENABLED = true
# Battery voltage below which a warning is emitted.
SAFETY_LOW_BATTERY_VOLTAGE = 9.0
# Battery voltage below which a critical failure is reported.
SAFETY_CRITICAL_BATTERY_VOLTAGE = 8.5
# Battery voltage above which a EMPTY BAT failure is cancelled
SAFETY_UNCRITICAL_BATTERY_VOLTAGE = 9.3
# Battery voltage below which a warning is emitted.
SAFETY_LOW_BATTERY_PERCENT = 9.6
#Battery voltage below which a critical alert is emitted.
SAFETY_CRITICAL_BATTERY_PERCENT = 0

 

Cell specific battery tables

You also need to change the battery percentage table to get an accurate reading. The table is slightly different for different battery packs, depending on the number and type of li-ion cells used.

Note! These tables are designed to let you use your battery to the fullest. There is very little “reserve” below 0% battery. Even before reaching 0%, your motor may produce less thrust and climb poorly due to the low voltage. Plan your flights accordingly.

Additional information can be found at:

https://github.com/uavpal/disco-docs/wiki/batteries

Samsung INR18650-35E/ LG Chem MJ1

3s3p packs:

BATTERY_PERCENTAGE_TABLE_LENGTH = 20
BATTERY_PERCENTAGE_TABLE_VOLTAGE = 8.5, 8.67, 8.81, 8.94, 9.17, 9.34, 9.51, 9.67, 9.81, 9.92, 10.1, 10.25, 10.83, 11.51, 11.69, 11.88, 11.98, 12.07, 12.17, 12.41
BATTERY_PERCENTAGE_TABLE_PERCENTAGE = 0, 1, 2, 3, 5, 7, 9, 11, 13, 15, 20, 25, 50, 75, 80, 85, 90, 95, 98, 100

• Never completely discharge Li-ion battery.
• Charge fully before first use.
• Never use force to install (insert) Li-ion battery.
• Use only a high quality battery charger.
• Do not expose to heat.
• Do not short (connect) positive, and negative battery terminals. Keep battery that is not in use in plastic holder (or any insulating container).
• Do not charge unattended unless using an intelligent charger that shuts off at full charge.
• Do not store your Li-ion batteries fully charged (for extended period of time).
• Store in cold and dry place.
• After battery is discharged don’t leave it discharged, charge it as soon as possible.