KINGKONG BLHeli USB Adaptor Unable to communicate with RacerStar RS40A V2 ESC

I ran into a problem recently where my KINGKONG BLHeli usb to ESC serial adaptor couldn't talk to my RacerStar RS40A V2 ESC.  Looking at the serial signal on the PPM pin, the voltage levels on the reply from the ESC wasn't swinging nicely down to 0V indicating the pullup resistor on the serial interface board might be a bit too strong.  

There is a 100 Ohm series resistor going to the SIG/PPM pin.

And a 3.3K pullup to +5V.  This is the resistor that needs to be changed.  I used a 6K 0402 resistor I had laying around and things worked like a champ.

Hope this was helpful to you out there.  Leave a comment if you have any questions or suggestions for future articles.

Thanks!

~pk

Cobra DL60A+ upgrade to BLHELI

I recently purchased 2 used Cobra 60A ESCs.  Turn's out that one of them was the older variant that needed a programming card to customize while the other one was newer and ran BLHeli out of the box.  Here's what you need to change to get the older variant to be flashable by BLHeli.


If yours has this sticker, it may be the older variant:

Here are the unmodified old and new PCBs side by side:

Old PCB

New PCB

Here are the components on the new PCB you'll want to pay attention to highlighted:

They have changed the circuit to replace existing diode output logic and pullup to a simple series resistor and a cap to limit input noise.

Zoomed in on the new PCB:

Hope this was helpful to you out there.  Leave a comment if you have any questions or suggestions for future articles.

Thanks!

~pk

TrueRC Singularity 1.2 Ghz - RF Performance

I wanted to do a few quick VSWR measurements on the TrueRC 1.2 Ghz Singularity antenna to confirm that it doesn't get detuned too much when embedded in a foam wing.

Here's the bare antenna:

It's an impressive little antenna. Centered nicely between 1258 and 1280.

And here it is in a VAS Sphinx that was sacrificed in the name of science :)  (Note: there there is only one fiberglass spar in the Sphinx.  I expect a Carbon fiber spar in the near field would detune the antenna, but that will be an experiment for another day)

Impressive! Almost no effect to the VSWR from the foam or the servo near by.

One thing to note (just for the sake of completeness):
VSWR (Voltage Standing Wave Ratio) is a measure of how much energy is reflected back from the antenna.  There are 3 directions that RF energy goes once is leaves the video transmitter.  1: A portion is radiated as EM energy to the environment (we'd love it if 100% went this way).  2: A portion is lost in the feed line or antenna itself due to resistive heating and parasitics (Since we don't have room temp superconductors just yet).  3: A portion is reflected back towards the transmitter if the antenna isn't a perfect impedance match to the transmitter.  The latter is what VSWR is a measure of.  So antenna efficiency can still be negatively impacted bit items in the near field of the antenna even if the VSWR isn't.

So, in the name of science, let's take a look at what's inside:

And just for fun, let see how much things get detuned when we sweep the antenna with the top cover removed:

Quite a bit.  But not too unexpected.  This info might be useful for those wanting to fly 1280 and 1320.

Hope everyone enjoyed the ride!  Leave a comment if you have any questions or suggestions for future experiments.

Thanks!

~pk

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Edit: Oct 29th, 2017

And here are some sweeps with a carbon fiber rod in the near field (~ 0.5 inches away from the edge of the antenna)

Reference measurement: Slot Cut, No CF rod present:

CF rod ends parallel to the edge of the antenna where the feed line enters:

CF rod ends at the midpoint of the antenna:

CF ends 1" past the end of the antenna: