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Élikos Polytechnique Montréal is a student club that helps students interested in the field of engineering to extend their knowledge of those available unmanned systems. As part of the electrical team, I made an interesting project which was to build a power distribution board with hot-swap capability.
Power Distribution Board (PDB)A PDB is simply a printed circuit board (PCB) that delivers power to the motors and also changes the voltage to 5V or 12V (or both) to power multiple devices like the flight controller or the on-board computer. It's now possible to find those for really cheap on websites like Banggood or Hobbyking but I wanted one** more feature that I couldn't find anywhere: Hot-swap.**
**one with the Hot-swap feature which I couldn't find anywhere so I made my own.
Hot-swapA major flaw in our previous drones was that the drone would shut down during the process of switching batteries. In that situation, the on-board computer took some time before booting up again which resulted in losing precious flight time during competitions. That's why I decided to use an OR'ing design to switch between two batteries in parallel.
DesignThe power distribution side of this project is simple to implement since components for DC/DC conversion are widely available online. This design includes a connector for the 5V power supply of a 3DR pixhawk flight controller. For the hot-swap feature, I based my design on the LTC4144 from Analog Devices. Basically, I have two batteries in parallel on my drone and the IC compares the voltage to choose the one with the highest one. When the voltage is the same for both batteries, the circuit shares the load between them. I also added an auxiliary laptop power supply (19V) to be able to power the entire system without batteries. This allows our team to program the flight controller and the on-board computer (OBC) without draining the batteries.
Unfortunately, this first version has a few issues. First of all, the documentation isn't very clear on how to use the STAT pin on the LTC4144. It should be able to trigger a light with a MOSFET when the IC is active but it didn't work in my case. I also used the wrong power supply voltage for the current sensor IC (12V instead of 5V) so this part of the circuit isn't working properly too. I updated the schematics for the next version. Stay tuned for version 2.0!
As always in student clubs, none of this would be possible without the financial help of our awesome sponsors. Thanks to all of them for investing in the future of passioned engineering students!
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