Blade CX2 Power problem, Need Help

[Knevel13]

Hello all,

Great forum. Just some back ground, I have been flying helis for about 6 months. I own a Blade CX2, Walkera 53-1 and 5G6. So I'm still very new to the hobby.

The issue; I crashed my CX2 and bent the fly bar and broke the lower blade mount along with the blades. I replaced the blade mount with a CNC one while I did this I went ahead and replaced the swashplate with the CNC upgrade. I bent the fly bar back and it seems fine (no vibration). After the repairs I only get about 3 minutes of flight time. I tried all my batteries and it is still the same. The rotors turn freely and it flies good. Any Ideas?

Thanks, Matt

[swatson144]

Hello Knevel13, and welcome to helitown.

A 3min flight is ~20C! Most of the packs for this class heli are 8-10C so your packs should be smokin' hot if the heli really is pulling 20C. Something is a little strange here cause assuming .8AH packs you'd be pulling 16A and I don't think there is a single part of a CX2 that can handle 16A.

So, I'd have to think we have a combination of troubles here.

How are you determining flight time? Lipo alarm? Diminishing performance? Skids won't leave the ground? etc?

How long did it fly prior to the crash resulting in the repairs?


Steve

[Knevel13]

Steve,

Thanks for the fast reply. Before the crash I got about the standard 8-10 minutes of flight time. Now the heli will start out ok but after about 2 1/2 to 3 minutes I notice a lack of power. I got out my volt meter and checked the battery before I started and it was 8.3 volts, at the end of the flight it was 7.7 volts. My battery is a 7.4 volt 800 mah, is it over charging? I'm using the E flite charger that came with the heli and taking the battery off as soon as the light shows charge complete. Regardless of the battery condition, this power loss happened right after the crash/repairs were made and I started flying again. The battery is not very hot when I'm done flying, just slightly warm to the touch. Thanks again for the help this one has me puzzled.

Matt

[swatson144]

A lipo is fully charged at 4.2V / cell. 2S * 4.2V = 8.4V so your charger is doing good.

With the CNC bits you added a little extra weight. Though in it's own that isn't enough to change the flight time that much. I have no idea how much weight but if you have a before and after AUW?

The battery is coming down what sounds like properly warm so we can rule out it drawing over the capacity of the pack, or it'd be hot.

7.7V resting tells me the pack is only reaching 50% discharged, which would seem to be indicative the pack not being able to hold voltage at hovering current. When Lipos get old and weak they tend to do this.

How old are the packs and how many? Do You have any one pack that has had a lot less use/much newer? If so try that one and if my guess is right I'll bet that one does much better.

The coaxial's pilots tend to be rough on batteries. Lipos don't like to be discharged below ~3-3.2V/cell under load which is hard to measure but that equals a resting voltage of 7.2V on your pack. They tend to last much longer if kept to only about 70-80% (~7.6V resting). Most coaxial pilots tend to kill their first packs pretty quickly by flying until the heli don't want to fly anymore and charging and repeating. later they learn that timing their flights to 7mins (assuming 10 to no longer wanting to fly) their packs will last hundreds of uses instead of several.

My guess is that the extra weight is the straw that broke the camels back, since you don't seem to be pulling an overly high current as everything turns easily, and nothing is landing hot. That's just a guess on what info I have at hand. If you do have a much newer pack and still have the same results I'd have to add perhaps something is dragging slightly to the combination slightly boogered gear etc.


Here's a chart,

4.20v = 100%
4.03v = 76%
3.86v = 52%
3.83v = 42%
3.79v = 30%
3.70v = 11%
3.6?v = 0%

Steve

[Knevel13]

Steve,

I have 3 batteries and rotate them. The oldest battery is 3 months old, the newest is about 1 month. Some work better than others but I'm pretty careful not to run them down too much. Your chart will help alot. The CNC upgrade weight is minimal, and I replaced the stock body with a lighter one so I don't think weight is the issue. Everything spins freely and all connections are good. Do you think it could be the 3 in 1? I'm going to go back over it with a fine tooth comb and I'll get back with you. Thanks again for all the help. Matt