Version vom 7. April 2015, 16:11 Uhr

Basic principle

By the help of the perimeter wire loop, the robot finds its charging station where it can be charged again. So, it drives along the perimeter wire (in clock-wise direction) until it detects a charging voltage at its charging pins. There the robot stops and recharges its battery.

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  Perimeter wire below charging station

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  Charging station components

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  Charging station

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  Sony Konion 7S2P battery pack (29.4V, 4500 mAh)

Charger

For the charger, we are using a Lithium Ion e-bike charger (29.4V, 1.5A current limitting) that can be purchased via the shop . The charger is placed in a protected area (house etc.) and connected to the robot charging station. The charger should accomplish the following things (in this case Lithium-Ion, lead battery is similar, but less critical):

• Charge battery pack via the charging pins of the robot
• Maximum cutoff voltage / charge voltage compliance (charging voltage limit)
• Maximum charging current compliance (charging current limit)

If you are using an existing charger, these things are implemented with high probability already in it.

Battery

For the battery, we are using a 'Sony Konion 7S2P' Lithium Ion battery pack (Sony Konion US18650V3 2250 mAh cells, Li-Mn), 29.4V, 4500 mAh, 500 recharge cycles, 126 x 36 x 65 mm (LBH).

Using this battery with the Ardumower motors, the mowing time is about one hour.

Undervoltage protection

The robot should be able to switch off the battery itself (undervoltage protection).

Idea:

• Emergency push button: can power-off the robot immediately
• POWER/START button: switches on operation voltage
• Arduino power signal pin (OUT): set to HIGH at bootup - set to LOW if undervoltage detected

battery (+) ---- emergency push button (emergency OFF) ----- relay switch ------ operation voltage (+)
                                                                  |
                                                                  |
                                                               control
POWER/START button -----diode-------------------------------------|
                                                                  |
Arduino power signal pin (OUT) -----diode-------------------------|

battery (-)

Robot

In the robot itself, the battery voltage is monitored (see diagram below). So it can be determined when the robot must go to the charging station. The robot and the voltage and the current during charging is controlled. So it can be determined whether the robot has reached the charger and when the battery is fully charged again. Ideally, the charging station also powers the loop transmitter:

charging station circuit:

 Power supply => Charger 24V (+)----- Charging station charger pin(+)
                 GND         (-)----- Charging station charger pin(-)
                 Charger 24V (+)----- DC-DC converter 5V  => Perimeter sender Arduino Nano  
                 Charger 24V (+)----- DC-DC converter 12V => Perimeter sender MC motor driver

robot charging circuit:

 Charging station (+)---+------+-- relais ---- current sensor ----- battery (+)
                               |
                               ---- voltage sensing
 Charging station (-)-- +------------------------------------------ battery (-)

Charge monitoring/Battery settings

Via pfodApp (Android) you can monitor the charging process.

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  Charging plot

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  Battery settings

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  Battery fully charged

Charging station ideas

Videos

1. Driving into charging station
2. Drive in and out
3. Tracking and docking

Further links