Robot Electronics
TODO Francisca
NEMO uses a LiPo (Lithium Polymer) battery as it's energy source (Lion Power brand). LiPo batteries are composed by multiple individual cells with a nominal (default) voltage of 3.7V. In our battery's case, it's a 3S (3 cells in Series). That means its total nominal voltage is 3*3.7 = 11.1V. However, the battery won't operate at that voltage at all times. Each cell cannot be discharged below 3.0V, or exceed 4.2V or else it might suffer damage or become unoperational (or sometimes explode). The battery has a main output, as well as a 4-pin connector. The 4-pin connector allows access to each cell individually, so we can check all of their voltages. The charger uses this information to balance all the cells.
The maximum allowed voltage is 3*4.2 = 12.6V. The minimum voltage is 9V, but a safety margin must be maintained. Usually, the H-bridge motor driver will stop working correctly at voltages too far below 12V. When in doubt, always check with a multimeter or battery checker.
The battery must be charged with a proper balance charger. We are currently using an iMax B6 balance charger.
1 - Place the wires in the main output holes of the charger. Always respect the color coding!.
2 - Connect the battery's 4-pin connector into the charger.
3 - Place one alligator clip into the battery's XT-60 connection and make sure it is the correct one, properly color coded.
4 - Secure the clip, and do not forget to use the protection around the metal contacts.
5 - Repeat the process for the other clip, and make sure they do not come into contact at any time.
6 - Plug the charger in and Select LIPO battery.
7 - Select BALANCE CHARGE. Then, set the charging current to no more than 4.2A. Set the voltage to 11.1V(3S).
8 - Hold the start button and confirm the charging if R and S match.
9 - ALWAYS be present while the battery is charging. DO NOT leave it unattended. DO NOT charge over 12.6V.
When in doubt, refer to the charger's manual.
This video contains more useful information about charging LiPos: https://www.youtube.com/watch?v=-cIsV4tqimc&ab_channel=CrazyHobbies
TBC... TODO
Ultrasonic Sensor HC-SR04 is a sensor that can measure distance. It emits an ultrasound at 40 000 Hz (40kHz) which travels through the air and if there is an object or obstacle on its path It will bounce back to the module. Considering the travel time and the speed of the sound you can calculate the distance.
The configuration pin of HC-SR04 is VCC (1), TRIG (2), ECHO (3), and GND (4). The supply voltage of VCC is +5V and you can attach TRIG and ECHO pin to any Digital I/O in your Arduino Board.
In order to generate the ultrasound we need to set the Trigger Pin on a High State for 10 µs. That will send out an 8 cycle sonic burst which will travel at the speed sound and it will be received in the Echo Pin. The Echo Pin will output the time in microseconds the sound wave traveled.
For example, if the object is 20 cm away from the sensor, and the speed of the sound is 340 m/s or 0.034 cm/µs the sound wave will need to travel about 588 microseconds. But what you will get from the Echo pin will be double that number because the sound wave needs to travel forward and bounce backward. So in order to get the distance in cm we need to multiply the received travel time value from the echo pin by 0.034 and divide it by 2.
