Sunday, April 26, 2015

The Tao of Nutball

Saw this here... GoldGuy is the designer of the NutBall, and apparently a student of Philosophy!

On NutBall.

  • Don't add anything that's not absolutely required.
  • Build light and you will be rewarded.
  • The reason why the NutBall is super simple is to keep it light.
  • The difference between a high and low wing loading is either no joy or pure joy. 

On Weight.

  • Be happy, build light.
  • Light is might.
  • Weight is the enemy.
  • Only slopers add weight.
  • Light is a delight.
  • That's, as in ballast... Although my belt size has grown.
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Tuesday, April 21, 2015

LED Spectator TV for FPV

RCGroups member UniversalRC shows his external video setup.  It runs on 12V and has a beefy tripod mount.  He uses it so his aerial video clients can watch the imagery he's capturing.

The monitor runs off of  4500 mAh 3S battery. Here's the tripod.

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Saturday, April 18, 2015

Inspire 1 in the wind, two flavors of video

Upgraded the Inspire 1 firmware, everything went OK.  Took the unit out, and was impressed with its stability in the breeze.

I'm terrible at guessing wind speeds, but I'm pretty sure it was 15 mph gusting to 20 mph.  Can anyone guess the windspeed by the flags blowing?

I recorded the video at 4k, 60 mbits/sec, and transcoded a copy to 1080p, 30 mbits/sec.  I've included both... does it make a difference once it's uploaded to Youtube?

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Sunday, April 12, 2015

My Cheap Ikea Workbench

I was talking with a friend, and it turned out we both had workbenches made from Ikea tables!  Here's my setup, which is both small and pretty cheap.

ADILS legs (4) - $14 ($3.50 each).  It's hard to see from the website, but it includes screws and a mounting plate.  The plate screws onto the table top, and the leg screws into the mounting plate.

It comes in a couple of different colors and is 27.5 inches long, just right for a sit-down workspace.

LINNMON table top -  $6.  It's nice because the table top is the cheapest part.  When it gets too beat up, just run down and buy another!  It's pre-drilled to accept the ADILS mounting plate.

Everything goes together in just a couple of minutes.

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Thursday, April 9, 2015

DIY DJI Inspire 1 Battery "Charger"

"DIY" is one of the watchwords here at EastBay RC, so you can imagine it's going to be an interesting experience to deal with a real store-bought system like the Inspire 1.

Our first project: a power supply for charging the Inspire batteries.  Here's the prototype, which is working well.

The DJI power supply has these features: rated output of 26.3V, 3.83A (100W), proprietary connectors for battery and radio.
In order to get the 26.3V, I'm using a boost converter.  It will take input from 4V to 25V and convert it to 26.3V. I got it on Amazon for $12.  You can get it for about $8 if you don't mind waiting for China shipping.  Specs on my unit are

  • 9A max input, 6A max output.

Double check the ratings for the unit you get.
We'll go into more details in a followup post about how to configure the boost converter.  Here's my initial test connectors.  They are two prongs from an old extension cord, and fit perfectly into the battery.  Positive is on the left.  I'll do a video with some more construction details as well.
 Here's a second connector.  I glued the prongs onto a piece of scrap wood and insulted with liquid tape.  I double and tripled checked the polarity was correct.
Here's the final connector.  It works really well!

I can now charge the battery using any 12V-24V power supply, including my regular charger on Pb mode.  Charging from the car should be OK as well, but I'll double check the amperage requirements.

Anyways, hope this quick note helped, and if you're interested in seeing more DIY Inspire projects let me know!

Power Equivalence.  The table below shows the required amperage at several voltage levels in order to provide the equivalent power.  The first amps column is the straight calculated equivalent, and the second amps2 column take into account the approximate 10% power loss from the boost converter.

Watts Voltage  Amps Amps2
100      26.3  3.83
100      24    3.3    4.5
100      20    5.0    5.5
100      18    5.5    6.1
100      12    8.3    9.1

Note that the 12V amperage is just barely within the maximum amperage specified for my unit, mentioned above.

If you have a standard RC 4-button charger, you can set it to Pb (lead-acid), 20V, 5A and be just a little shy of the maximum equivalent charging capacity.

There's a rumor that the built-in charger of the smart battery won't current-limit. Sadly, too much of the DJI world runs on superstition, so until a battery dies and we get to do an autopsy, we won't be able to determine if this is true.  In the meantime, if you don't exceed the  Amps2 number for your power supply voltage that won't be an issue. (update: see below)

(Update) Some people have asked why "Charger" is in quotes in the title.

  • The technically correct terms are "power supply" for the thing that plugs into the wall and "charger" for the circuitry that supplies electricity to the cells.  This is also the common industry usage.  A typical RC charger includes the circuitry to properly charge "dumb" LiPo batteries.
  • DJI uses the arguably "technically incorrect but more commonly used" term "charger" for the power supply.
  • Displaying EastBay RC's famously pedantic nature, we therefore put "charger" in quotes.

(Update) DJI has some good information on their wiki.  Specifically, this datum:
7. Over Current Protection: Battery stops charging when high amperage (more than 10A) is detected.
If this situation is detected, the document indicates that LED2 will blink twice per second.

So the total power provided to the voltage converter should be under 260 watts.

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Tuesday, April 7, 2015

Things to try: the Dream Flight Libelle DLG

Rather sweet, and not crazy expensive like so many DLGs.

"There are few experiences in model aviation more satisfying to the soul than flying an efficient, slow-moving glider that has been launched to soaring altitude by hand. The Libelle takes RC hand-launch glider flying to the next level, building off of the global acceptance of the Dream-Flight Alula. Until now, this type of experience had been out of reach for many pilots for a variety of reasons. The Libelle is for everyone; it can be assembled, balanced, and trimmed for flight by pilots of any experience level."

Lots of info here:

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