After watching too many videos of LiPo batteries catching fire, I was really uncomfortable with the thought of flying with a potential fire hazard that could melt the harness or the glider lines. That would be an extreme scenario, but looking at the size of the balls of fire that lipos can produce, it didn’t seem like a good idea. Here is my attempt at a poor man’s ejectable battery box.
This box fits 2 or 4 of the 6s 22000mAh LiPos (like the Bonkas).
It uses the existing holes on the back plate of the frame for support.
thought about making it aluminum, but saw lipo fires documented at over 1300 F and lasting over 15 minutes. Aluminum would melt at around 1200 F. So, I went with steel. Heavier, but withstands about 2500F. Some of the High temperature resistant (fire proof) carbon fiber would be the ideal material, but I couldn’t find any. Plus, it seems like even if the carbon fiber itself resists the fire, the resins might not, so it would have to be some very specific material.
No welding used. It is all steel rivets connecting Home Depot 0.019 Steel Sheets. Finished with decorative carbon fiber vinyl.
Wanted some sort of mechanism to eject the box in case of fire.
the bottom is opened, to try and release pressure in case of fire. The opening has a flat to try to divert the fire/gases down and back, away from the pilot / harness / glider.
Total weight - 1540g
Hope to inspire someone with a lot more talent and tools.
I have tested the contraption and it releases upon pulling the ejection cable. So far, my tests have not shown the batteries to get hot, but I have not done a full throttle till the battery dies. That is one thing I worry, wether the batteries are going to get hotter because they are in a closed box.
This is coming out of my unit as soon as Paul releases the official OpenPPg battery box.
That’s right. I was trying to come up with some mechanism to do that. Then I once I was testing the resistance on the pin and forgot that the batteries where inside. I pulled the pin and the whole thing came off. It worked.
Of course, in a real life situation, there will be some degree of the props hitting the box as well.
Very simple, the bottom part has an angled 1in wide tongue(covered with sticky Velcro to protect the frame) that hooks inside one of the frame holes. The box rests on top of two of the frame screws.
There are 2 rubber donuts that create pressure pulling the box away from the frame. Finally, another metal tongue slides into one of the slots and is held in place under pressure by the pin.
It might just work. Don’t know how long it would take or if the weight of the battery alone would make it fall vs. dangle on fire on your back / legs. But eventually it would melt the connectors and fall off.
So, the box need to tilt back a little before it falls off. Ideally it should fall straight down.
It seems like the 2 bottom props would not stop the fall, as any inclination from the top part of the box would probably just spin the bottom props out of the way.
There is an angle at which the 2 top props could catch the box as the overlap the box by about 5 cm. I think if both too props are in that position at the same time they would prevent the box from falling. If it is only one, it should not be a problem, as the box would fall to the prop free side, turn and spin the blocking prop out of the way.
I think it would be unlikely that both top props would be at the critical position at the same time.
If they do, I would wiggle in the harness and swing the glider.
But ideally, in a better design, the box would just fall straight down.
That article, serves one purpose only to me, regular intervals of checking if batteries are overheating. This person used them for yrs without an issue. Tendrils, or what ever they call those internal growths, finally got to long and bam, fire
So I’m working on and ESP32 for the flight computer now. It will monitor RPMs, current, voltage etc. It will also talk to the BMS chips, which have temp monitoring built in via thermistor. So that should do the trick.
I intend on sharing it. To start I’m going to use it to get a better understanding and optimize my machine, but hope to be able to produce them for others too. What kind of features would you be looking for?