Battery

Each arm is going to be powered by a lithium polymer battery. This sort of battery has been chosen due to the great amount of electrical current needed to power the devices, especially the robotic manipulator.

Model: Turnigy 5000mAh 35C 3S

Minimum capacity:5000 mAh

Configuration: 3S1P / 11.1V/ 3CELL

Constant discharge: 35C - 175A

Discharge peak : 45C - 225A

Pack weight: 0.430 kg (0.95 lb)

Pack size : 145 x 49 x 25 mm

Charger plug: JST-XH .

The model of battery which is going to be used must not work under 3 volts per cell, so a protection circuit is required in order to prevent that situation. While charging, we need to ensure that the voltage is identical in each cell because, when charged, the total voltage is around 12.7V, if the cells are not balanced, a cell can exceed the maximum voltage supported, which may lead to permanent damages in the battery such as exploding or fire. Also, when using the battery, there will be an electronic circuit capable of doing several functions.

It is going to be used a fuel gauge based on the bq20zXX series, produced by Texas Instruments, it constantly reads the battery status such as available charge, battery voltage, current and temperature. The Fuel Gauge circuit uses SMBus 1.1, in order to have a computer communicating with it, a circuit capable of converting SMBus to USB is needed. At first, it is going to used the EV2300, also produced by Texas Instruments, it is included in some of the bq20zXX Evaluation Modules, sold ready to use, it also includes a software to use with the fuel gauge.

The project’s components are not going to have the same powering system.

• The arms are going to be powered by the lithium polymers battery
• The hokuyo is going to be powered by the netbook’s battery
• The roomba is self-powered by a 3000 mAh 14.4 v NiMH battery.

The project's specifications don't allow access to Roomba's power button, to solve that, we need to place an external button.Through the DB-25 port we have access to roomba's battery and the power toggle, when there is a transition from low to high the roomba changes its on/off status. A pull-down resistor is connected from ground to the power toggle pin and the button is connected to the roomba's battery pin.

There will be the option of turning Roomba off remotely, in order to make that possible, an ASK receiver module is going to be included in the power control circuit and an ASK transmitter module will be on a remote controller board.

The Mini-din port used to communicate with the Notebook is not in a good place, we can connect the cables coming from the computer to the DB-25 port, that is going to be on the power control circuit too.

By doing that, we integrated some isolated circuits in a single box connected to the port located inside the empty space on Roomba. The fuel gauging system, though it's not connected to Roomba directly, will be inside that box too, that increases the free space and makes connections easier.