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Old Dec 06, 2009, 04:02 PM
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Walkera 4#3B double brushless on diet - how I got +100% of flight time

Hello

I've started with basic Walkera 4#3B version, which I've soon upgraded to brushless main motor. Recently, after some frustration with brushed tail motors failing one after another after replacing the first one (which lasted quite long), I decided to go for a brushless tail as well. Altough equipped with both brushless motors (all Walkera accessories) my heli looks like some Dr. Frankenstein's creation, with all these ESCs and cables, everything worked quite fine with one exception: flight times. Using 600 mAh 15C LiPos I was only getting mere ~5-6 minutes of flight times on average, 8 minutes tops. Most presumably that was because of the increased weight. My fully upgraded heli weighted about 51 grams without battery. I've decided to do a few minor tweaks in an attempt to reduce some weight. After that my 4#3B ended up weighting some ~2-2.5 grams less (49g without a battery) which I was afraid wasn't enough to yield noticeably longer flight times but to my surprise, I've suddenly got consistent flight times of over 11 minutes which in some cases is over double the original times!

Here are the photos of my modifications, along with some comments:

First of all, I've cut the redundant power cable with the battery plug (no longer used with brushless main) from the 4in1 module:

We're getting a little less clutter as an added benefit. Take care not to short the wires accidentally by non-clean cut.

Then, I've got rid of the power connector between the main motor ESC and the motor itself and carefully soldered the wires directly, securing the joints with some shrink tube:

Do not mix the cables and do the soldering well as there's some serious current involved.

Similarily, I've replaced the tail motor connector with a soldered connection:

Note the cable colors and take care not to break the delicate wires while removing the original plug.

Lastly, I've also replaced the battery to ESCs (both main and tail) Y-cable plugs with - yes, you've guessed it - good ol' soldering:

Triple-check the polarity (black to black, red to red), insulate properly! And again - do the soldering well so it could pass all these amps without problems.

A word of comment here: I suspect that my surprisigly good performance gain could be accounted not to the weight reduction alone. It could be that the original power connectors (ESC to main, battery to ESCs) don't cope with high currents well enough and by replacing them with a reliable soldered connections, we eliminate a possible weak link in the power transfer circuit. It is quite hard for me to believe that mere ~4% weight loss resulted in such a difference in flight times so I strongly guess it could also have something to do with the resistance of the original connectors. Especially the Molex-type one used for powering the main motor was definitely designed for conducting way smaller currents (they're very common as the PC case LED connectors and such).

I hope it helps someone unleashing the full potential of their 4#3B - in my case it was definitely worth the effort (but needless to say, I take no responsibility for any improper implementation of any of my tips). You don't replace your motors and electronics every few flights so I guess the loss of the connector-type cable joins is a completely reasonable tradoff.

Regards
Zbig
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Last edited by Zbig_T; Dec 06, 2009 at 04:58 PM.
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Old Dec 06, 2009, 09:44 PM
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Wow that's a big difference! may I ask do you have a 500mah battery to try your flight time on? I'm curious to know. (might get a double brushless 4#3)
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Old Dec 07, 2009, 08:25 AM
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Originally Posted by XXXmags View Post
Wow that's a big difference! may I ask do you have a 500mah battery to try your flight time on? I'm curious to know. (might get a double brushless 4#3)
Just checked - now I'm getting solid 7:something minutes from 500 mAh LiPos (already worn out to some degree) instead of the average 4-6 minutes from before.
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Old Dec 07, 2009, 01:11 PM
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Joined Dec 2002
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Just for interest, for the same rotor system, the Power required to fly is proportional to the weight to the three halves power.

POWER ~ WEIGHT^3/2

Using this formula will indicate how much of your increased flight time is due to a weight decrease.
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Old Dec 08, 2009, 01:25 PM
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moving comments
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