The FVT Little Bee ESCs, also known as the MRM Zeus, are very popular ESCs for mini quad pilots right now, and for good reason. They perform very well and at a reasonable price. However, there is one issue with these ESCs – they cause some nasty voltage spikes that can fry FPV cameras and video transmitters. I will try to explain why this issue occurs as well as how to fix it. Feel free to skip the next paragraph if you want a fix without any of the technical details.
Most ESCs have one common feature – they have a large electrolytic capacitor sticking out of the back. This is to absorb the voltage spikes that come from the operation of the ESCs. However, to make these ESCs smaller and lighter, FVT used surface mount ceramic caps instead of electrolytic ones. Usually, these would be more effective at absorbing spikes due to the lower ESR, but they aren’t. This is because these capacitors may not have been sufficiently derated. Derating is when you use a capacitor rated for a voltage 2-3 times the maximum you expect the capacitor to see since the effective capacitance decreases as you get closer to the max. operating voltage. This is significantly worse for ceramic caps than for electrolytic ones. All ESCs with active braking generate these voltage spikes, but it especially bad with the Little Bees due to the combination of extremely strong braking and insufficient filtering. A huge thank you to mnemennth at RCGroups for the explanations.
Now for the fix itself: One option is to add one large capacitor (1000 uF or more) where your battery wires connect to the PDB. Make sure the voltage rating is high enough! You can also add small capacitors (around 330 uF) where each ESC connects to the PDB. The exact values are not crucial but should be in this range. Ideally these should be low-ESR caps of a good brand like Panasonic, Sanyo, Nichicon or Rubycon. Basically what you are doing is compensating for the insufficient filtering by adding more (to soak up the spikes). I have not tried this method myself but have heard from reliable sources that it works.
An easier method which worked equally well (for me) was to power the FPV gear from a small variable buck converter like this. It is a good idea to buy a 5 pack since they are dirt cheap and super useful to have around. Note that this is a buck converter, which means that the input voltage should be higher than the output voltage for a stable output (usually about 1.2V higher). I set the voltage on it to 9V to be safe as I run both 3S and 4S which means that the input voltage may sag up to 10-11V during hard flying. Do make sure that whatever output voltage you set is at least 1V above the minimum voltage required by your video transmitter and FPV camera to avoid blackouts. I also put a 470 uF capacitor on the output of this regulator for more filtering. I get nice clean video feed and haven’t fried anything so this method seems to work for me. Ideally, you should still use a 1000uF low ESR cap on the power rails in order to protect the regulator itself.