Sunday, March 2, 2014

Hexacopter Power Distribution Board

New PDB. It ain't pretty but it should work.

Recently my hexacopter crashed. Luckily I had a GoPro strapped to it and I saw one of the motors stop in flight. You can also hear a"pop" just before the failure.

After the crash I plugged the suspect motor into a good speed controller (ESC) and it worked fine.  So I plugged a good motor into the suspect ESC and it did not spin. Therefore, I concluded that the ESC had failed. I took the ESC apart to see which component failed but I couldn't find anything out of the ordinary.
But when I installed a new ESC, it didn't work either! After a little checking with my multimeter, I discovered that the positive terminal on the power distribution board (PDB) for that ESC was not getting power from the battery. Upon closer inspection, I could see that the circuit traces had burned out. This was a bit surprising considering that the board is rated for 90 amps and my motors should only be pulling around 45 amps max.

Note the 3 burned copper points around the lower right solder pad.

I had a few choices to fix it. Purchase the same thing again, purchase a different one, or make my own. I couldn't put the fate of my several thousand dollar hexacopter in the hands of the same component that failed once already. Other brands were an unknown and probably would not fit as well. I really liked the form factor of the original so I decided to make my own based on that design. I could etch my own PCB but I was concerned that it couldn't handle the power. So I decided to make a new PDB out of a piece of 0.025" copper plate. That's five times thicker than the original copper traces. It should have no problem handling the current.

I choose a piece of 0.093" polycarbonate to insulate the positive and negative sides. I marked and cut the plastic the same size as the original PCB. Then I cut out two pieces of copper plate larger than the plastic.

I glued the copper pieces to the plastic with 5 minute epoxy then trimmed the copper even with the plastic.

Each copper plate is almost as thick as the old PDB!

With that finished I drilled the mounting holes with a 1/8" drill.  I'll use nylon mounting screws to avoid any shorts. I followed by drilling a hole for the negative battery lead. The negative lead was passed through the bottom of the board and soldered to the top. I soldered a set of 3x6 header pins to the negative side of the board for the ESC receiver wires. All of the negative leads are wired together. The positive leads are separate. One positive lead is wired to the power supply wire for the flight control system. And the wiring harness from the old PDB was soldered to the signal wires.

Ready for ESC's
Finally, the six ESC's were soldered to the board. I covered the entire board in several coats of liquid electrical tape. Once it was dry, I screwed the new PDB to the center plate and attached the receiver leads. It fits the hexacopter exactly like the original. It is a little heavier, but this one can handle much more power. Now I just have to slap it back together and get her back in the air.

Ready for reassembly.

Tip: If you've never soldered to copper plate before, you need lots of flux and lots of heat. Coat the area to be soldered with flux. Heat it thoroughly with your soldering iron. Keep touching solder to the area until it melts. When it does, run your soldering iron in circles around the area to tin it with solder. Once you have a small layer of solder on, it will be much easier to solder your leads. Don't try to solder leads directly to bare copper plate.

1 comment:

  1. Interesting blog with nice posting,it really give the machinery ideas which is very interesting for me.
    Electrical Distribution Boards