The Plan: Diagramming the Electronics

Written 2018-08-26

This post is a high level description of the electronics I used - it’s not necessary to make the build that I did, but it’s meant to be helpful in understanding why I made certain decisions.

The Big Picture

diagram

The big picture for the electronics is for a charging system to supply power to two different battery systems. One battery system will power the motor, and the other will be for the lower power electronics, such as the lights, bluetooth reciever, and circuitry used to control the motor. The high power and low power electronics are run off of different batteries mostly because I had three different batteries. You could just use the bigger battery system and run the lower power electronics off of regulators and buck converters, such as in the following diagram:

diagram

Battery and Charging

diagram

Let’s take a deeper look at the charging system. On the low power side of the electronics, we have a buck conveter - this efficiently changes the 24 volts from the power jack to the 11.1 volts the 3S battery expects while charging. The buck converter I got is also CC CV. This means that in addition to having a knob to adjust voltage output (CV - constant voltage), the buck converter has a knob to limit output current (CC - constant current). Lipo batteries are generally charged using a CC CV supply, as an excess of charging voltage or current can harm them.

On the motor side of the electronics, we have a boost converter. This will efficiently change a lower input voltage (24 volts from the laptop charger I have) to the 25.6 volts expected by the bigger 6S battery. The diode following the boost converter will stop current from travelling backwards towards the other side of the electronics. If the diode wasn’t present, the 6S battery would end up charging the 3S battery, damaging itself as its own voltage sank lower and lower.

Each battery also has a voltage monitor and a balance connected. The balances ensure that the cells in a given battery are at the same voltage (this increases the lifepsan of the battery), and the monitors go off if the battery they’re connected to is dangerously low on charge.

Low Power Electronics

diagram

Zooming in on low power electronics side, after the battery, we have a switch to power the board on and off. Then a buck converter changes the 3S battery’s 11.1 volts to 6 volts, which the lights and Arduino are happy with. It’s important that the buck is after the switch. If the switch was after the buck, then even when the board was off, the buck would consume available power for its indicator light.

The Arduino is the brains of the board - it runs code to control everything else. This is because optimally, all of the electronics on the board would be controllable via Bluetooth. The Arduino takes input from the Bluetooth module, which it also powers. It also has a control wire running to the speed controller for the motor. One drawback to the Arduino’s centrality is that if the Arduino becomes too busy with one particular task, everything stops. For this reason, it might be wise to use two Arduinos in the future.

The lights are controlled by the Arduino, but powered from the buck converter, as they can use up to 7 amps of current. They’re just for show.

The piezo horn is pretty straight forward - it takes a DC voltage in, and makes a loud noise. It might be wise to power it through a relay in the future - it operates with 5 volts to 8 volts, so it doesn’t reach its noise potential using the Arduino’s 5 volts.

The motor relay is actually two relays. The first relay controls the programming button on the speed controller, and the other can be used to switch the speed controller on and off. The relay board is powered using a 5 volt regulator, since the board pulls more current than the Arduino can handle

High Power Electronics

The electronics on the high power side are pretty simple - the 6S battery powers the electronic speed controller, which powers and controls the motor. The speed controller is controlled in every way by the Arduino using relays.

Parts

Parts Total: ~$369

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