Arduino quadcopter pilot - Odd LiPo battery behaviour


I've got an Arduino Nano hooked up to 4 brushed DC motors in an attempt to build a micro quadcopter. The whole thing is powered by a 3.7V LiPo battery (240mah, 20C, 1S). Since the battery only provides 3.7V I also have a DC step up board that provides 5V to the Nano.

When I plug the battery in and having uploaded a sketch to run the motors at 50% speed, the whole system runs for about 5-10s and then stops. During that time the motors are decreasing speed. Once the motors stop completely there is no power anywhere on the system. In fact the battery is no longer providing any power! Initially I thought that the battery had lost its charge but hooking it up to a charger for 1-2s is enough to repeat the whole process.

Hooking up the battery directly to a motor works fine and the motor runs at full speed. The battery comes with a protective circuit and I'm suspecting that something 'trips' on that circuits and cuts off power. Hooking it up to a charger 'resets' it and it starts providing power again. I've read in a couple of places that LiPo batteries with protection circuits can go into a 'protection' mode, but I think I understood that to mean to protect from undercharging (which is not what's happening in my case).

My next thought is that I'm perhaps drawing too much current....which I'm finding hard to believe though. I measured the pull from a single motor to be 65-70mA. So 4 of them would be 280mA plus whatever the Nano, the DC step up and the other components (gyro, RF24) draw. The problem is that when I hook up my multimeter between the battery and the copter it measures 45mA but the system doesn't quite run! it sort of kicks off a little then dies, then kicks off again, each time the motors spinning for like 1 degree. Take the multimeter out and it's back to the original behaviour (run for 5-10s then die).

Any ideas what's going on? Or something else to test?



Usually using a battery pack with protection, in a power hungry setup like yours, will not work.

The only quadcopter that Iknow of, which empluys a protection circuit is the AR-Drone - and it's a beefed up circuit, that can handle that kind of current.

The reason why you cannot stick your multeter in series with the circuit is "burden voltage" - google it.

There is a device called uCurrent (by Dave Jones, EEVBlog) - that fixes that issue.

// Per.

Most LiPo battery protection circuits have an overcurrent shutdown as well as undervoltage. There are a number of them with current settings ranging from 1 to 8 amperes, so you might be able to find one that will allow your motors to run. Here is a collection: Tenergy Battery Pack PCB

You battery is inadequate I think - its only rated for 5A, you might want to consider something
more like 2.2Ah 30C as being suitable for four motors. But how big is the 'copter? Which
motors and ESCs? total weight, motor constant and prop size?

A reasonably sized quadcopter, with 8" propellors is likely to need 100W to hover - which
from a 1S pack means 30A (3S at 10A would be more likely)

So either your 'copter is tiny or you've underestimated battery power...

Thanks for your replies.

My choice of battery came from looking into how other people have put together their copters, like this one for example :

There they say that they do use a protection circuit module, but perhaps it has more suitable specs. I don't even know what the specs of mine are, it's was a bit of a random ebay purchase! :slight_smile:

My quad is weighing in at 56g at the moment which is heavier than I'd like it to be (other designs are 28g!) so I'm hoping that the little 240mah LiPo should be enough for a few minutes flying.

I'll lookup burden voltage and see what I find! Thanks for the suggestion.