I'm currently building a quadcopter from parts and I'm writing my own control software.
I wasn't really familiar with RC components before starting this project, but I must say I'm impressed with the performance and reliability you get from very low cost motors, ESCs, propellers, gyroscopes and accelerometers.
However, I think Li-Po batteries are a huge safety issue. There are multiple factors:
* The battery chemistry is very unforgiving. You overcharge, it gets damaged, you over-discharge, it gets damaged. Same for charge and discharge current. The failure mode? Flammable gasses are released and eventually the whole thing sets itself on fire. And that's a fire you can't extinguish using typical means like water or regular fire extinguishers.
* All RC Li-Po batteries use a soft shell. If your model crashes the batteries can and will get crushed, which leads to an internal short-circuit, which eventually starts a fire.
* No RC Li-Po batteries incorporate Smart Battery controllers (like in laptop batteries) which could prevent overcharge/over-discharge and over-current conditions.
There have been plenty of incidents involving Li-Po fires, including whole houses burning down.
And still, the batteries don't change. Li-Po makes perfect sense for RC applications because it has great energy density and allows high discharge current. But to me it looks like some simple safety features could make this technology safe enough that you wouldn't have to treat your batteries like small bombs.
As a side-note, I've initially tried to use laptop Li-Ion batteries for my quadcopter. Each motor + propeller unit requires almost 12A @ 11V when at maximum speed - quite typical power requirements for a medium-sized quadcopter. I couldn't get more than 16A out of an older 6 cell battery (voltage was abruptly dropping if trying to draw more, so I guess this was the limit of the cells). I've then tried a new 9 cell battery (which was too heavy anyway). The controller on this battery considers 20A discharge an over-current condition and shuts off the output. So I'm stuck with Li-Po batteries and hoping that they won't set anything on fire.
I certainly wouldn't feel comfortable with current-technology Li-Po powered vehicles flying around a city without being watched.
I've built a few high performance rc cars and lipo batteries terrify me for all of the reasons you said. It seems like they are always just a hair away from bursting into uncontrollable flames. I quit using them because I was afraid to leave them at home unattended. I wouldn't want a swarm of these flying over my city.
No technical reason really, it's about cost, demand and volume.
Cost is going to be a problem because of the high current involved in normal operation and even more so in case of a short-circuit.
Let's take a popular battery size, let's say 2200mAh 3S 25C. This battery should be able to safely support a discharge current up to 55A. For reference, a 10KW power shower draws less current than this from the mains network. Our smart battery controller needs to be able to measure the discharge current, and needs to be able to switch the output on or off.
You can just buy a hall effect based current sensor and a power transistor that will handle 55A. But these components need to survive in case of a short-circuit for long enough for a micro-controller to read the current at its regular polling rate and then turn off the transistor. Expect the short-circuit current to be a number of times higher than 55A.
So you end up with a parts list that costs you about $10 per unit for small quantities (500). Have I mentioned the price of the battery I was building this for? It's $13.
I've thought about building some for myself, but 1) they really should be mounted inside a hard case together with the battery and 2) I don't have a space where it would be safe to prototype this, assuming that a failure will happen.
I'm currently building a quadcopter from parts and I'm writing my own control software.
I wasn't really familiar with RC components before starting this project, but I must say I'm impressed with the performance and reliability you get from very low cost motors, ESCs, propellers, gyroscopes and accelerometers.
However, I think Li-Po batteries are a huge safety issue. There are multiple factors:
* The battery chemistry is very unforgiving. You overcharge, it gets damaged, you over-discharge, it gets damaged. Same for charge and discharge current. The failure mode? Flammable gasses are released and eventually the whole thing sets itself on fire. And that's a fire you can't extinguish using typical means like water or regular fire extinguishers.
* All RC Li-Po batteries use a soft shell. If your model crashes the batteries can and will get crushed, which leads to an internal short-circuit, which eventually starts a fire.
* No RC Li-Po batteries incorporate Smart Battery controllers (like in laptop batteries) which could prevent overcharge/over-discharge and over-current conditions.
There have been plenty of incidents involving Li-Po fires, including whole houses burning down.
And still, the batteries don't change. Li-Po makes perfect sense for RC applications because it has great energy density and allows high discharge current. But to me it looks like some simple safety features could make this technology safe enough that you wouldn't have to treat your batteries like small bombs.
As a side-note, I've initially tried to use laptop Li-Ion batteries for my quadcopter. Each motor + propeller unit requires almost 12A @ 11V when at maximum speed - quite typical power requirements for a medium-sized quadcopter. I couldn't get more than 16A out of an older 6 cell battery (voltage was abruptly dropping if trying to draw more, so I guess this was the limit of the cells). I've then tried a new 9 cell battery (which was too heavy anyway). The controller on this battery considers 20A discharge an over-current condition and shuts off the output. So I'm stuck with Li-Po batteries and hoping that they won't set anything on fire.
I certainly wouldn't feel comfortable with current-technology Li-Po powered vehicles flying around a city without being watched.