Tuesday, July 21, 2015

Nano CPX upgrades

Ah, the Blade Nano CPX.  This thing is a wiley little bugger.  It's so light that it really doesn't want to hover.  It also is massively affected by room air currents.   

And yet.. I still love to fly it.  At least, when I can fly it. I made a mistake.  I decided to upgrade it, in hopes of getting better flight time.  Brushless motors are more efficient, and I thought I could help my desire to fly longer by installing the Horizon Hobby Brushless upgrade kit. 

....  I was wrong.... 

First off, lets talk about the installation.  The manual for installation doesn't go into great detail.  It shouldn't have to, as, at least in theory, the install is easy.  You unplug the stock brushed motor, and slide it out of the airframe.  You slide in the brushless motor, tape the ESC to the 5in1 board.  Next you plug the orange wire into the 5in1, being sure to match the colored dot.  Finally, you plug the power harness into the stock battery plug. 

But that misses at least one important step.  The motor clocking matters.  When you install it, make sure the motor leads come out of the motor as close to the 5in1 board as you can. 

Now you'll notice that there's no accessory harness in this picture.  I have wired the ESC directly to the pads on the 5in1 board where the stock battery connector goes.  This is because that accessory harness ruins the helicopter.  

Allow me to explain.  The 5in1 board has a low voltage cutoff built into it.  To save those expensive little 150mah batteries that Horizon Hobby sells.  This, is a very good thing.  Now the difference between a "good" battery, and a "done" battery, is a few tenths of a volt.  The connectors they use for these batteries, are not exactly high current connectors, so are pretty poor as plugs go, resistance wise.  The wires they use to bring power to the 5in1 board, are also very light gauge. 

This means there's effectively a string of resistors between the battery, and the 5in1 board.  And between the 5in1 and the battery there's this ESC that's trying to suck all the power it can from that tiny little battery. 

Any time there was a big load on the motor, the helicopter shut down.  I tried a variety of batteries, attempting to keep the voltage up under load.  The 25c 150mah cells wouldn't even spin up the rotor.  The 45c cells would work, if it was one of my fresh 45c batteries.  I also tried an aftermarket Lectron Pro 180mah 35c cells, and that had the best results. 

However, even under the best conditions, I was getting less than two minutes of flight time.  And we're talking just gentle hovering. 

After some digging around, I found that people had some good results with bypassing the harness.  I really didn't want to make any permanent modifications to the Nano CPX, but I also wanted my $60 brushless kit to work.  So I cut off the harness.  And I soldered the power leads from the ESC to the most sane place I could think of.  
I also read, that some people are flyign the Nano CPX on the 250-300mah cells from the MCPx.  ... I'll be trying that as soon as I can get a harness to adapt the plugs.  I anticipate eight or ten minute flight times. 

In the same package as my brushless kit, I ordered some landing gear.  They look great, and have a tail support boom.  They very seriously make the whole helicopter more rigid.   However they're also significantly heavier than the stock gear, something like three times the weight. 

Well they look good off the Nano CPX.  They're not going back on there. 
 Now.. I need to tune the pitch and throttle curves.  And maybe learn to flip this thing.   

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