This voltage protector offers 3,300,000 uF of energy storage in a small and lightweight package.
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more powerful multicopters bring us the opportunity to use bigger cameras, very big and complex gimbals, and of course big and powerful servos.
a servo, being a motor, needs a big available "immediate" energy, which means high current, when it starts moving.
capacitors are used to store energy for fast discharge application, and most of us know the "voltage protector" devices for RC, which are usually about 10,000uF capacitors that are plugging in the RC receiver and will give more stability and stored energy,
with the latest developments of EDLC (electric double layer capacitors) and high energy capacitor,
the ability to use them in the RC field is now possible.
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Comments
It is one of those "it is not really needed, but since it doesn't hurt let's use one to be sure" things. If you really need one it is more an indicator that you should get a bigger ESC.
I also see some possible problems with using a capacitor.
Firstly, a large cap will take a lot of current to charge when you power up the system. This could be bad for the ESC in the long run, being maxed out for a short time every start-up. So bigger is not necessarily better.
Secondly, if the spike is large enough to drain the cap you could end up getting an even worse after spike when the ESC have to recharge the cap and drive the servos at the same time.
@ John, that is exactly what I'm doing. Just ordered 4 2S rated servos, and I'll round-file the UBEC. It's the simplest solution.
@Gareth, I have the large "voltage protector" from Hobby King, and it can power the APM for 2 seconds, IIRC.
Now, one thing that needs to be said, is that I fear these large cap banks might actually introduce noise into the system. I think I've read that they can pick up EMF and convert it into voltage. I know that I have in the past left my big cap-bank unplugged for a month, then plugged it into my APM, and the power light turns on for a second then dims. It got that voltage from somewhere.
This large capacitor can probably power it for a long, long time.
For this type of application (big servos) there is another solution that might be simpler and also give better reliability, by using less electronics. Get some "high voltage" (HV) servos that can be driven by a 2S lipo directly (or 2S LiFE if you want lower voltage). No need for a ESC.
Nice low weight ~10 grams, with massive charge!
Could use a single Cap on small (9-12 gr) 4-Ch servos setups, just add it to ESC output connector in parallel, or to a Y servo cable.
The power demand spikes may be the cause of some APM resets, If it happens In the air it can be a disaster, I found this out the hard way from my original AurduPilot 168 re-seting in air. I set Mode to Manual, while AP was busy rebooting, it ignored my command, I watched my StevensAero SportStik (balsa/ply wing & carbon stick) dive and dig a hole in the ground !
I salvaged it for more torture during AP-328 test flights. Now with $20 Castle Creations UBEC and a small $3 super cap 0.1 F, It is air worthy still.
Damage was bad:
Wing was crushed up to main spar on port side,10 x10 cm carbon fuselage shattered, GWS 4:1 gear box destroyed, APC 11x3.8 prop snapped, one servo stripped, Landing gear fractured, All other electronics survived.
No more power glitches ... Yet...
How long would this power a APM for?
Bernard, that is correct. I'm sure there are caps in the circuit already, but in my experience, they are still not enough sometimes. Usually when an Xbee is on the frame, all the standard electronic design rules are invalidated. ;)
Bernard, true, but one should assume every basic circuitry has a low value capacitor in it to filter noise.
this is more for heavy consuming "power hungry" devices
Reduction of noise and compensation of sudden high current are not incompatible.
Connecting a 3F capacitor in parallel with a .03 uF should achieve both objectives?
I did not test any of this but somebody must have done it some ware ...
you would get better results with smaller "LOW ESR" caps, which are designed to have very fast charge and discharge rates (for filtering out noise)
yes it is zoomed, but these spikes are still very big relatively,
it's that short actual moment when the motor's coil is being connected and draws a lot of power, just before the 5v regulator detects the lower voltage and start to compensate.
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