SkyCadet's blog archive for January, 2013 - RC Groups
Archive for January, 2013

# Linearization of servos, and expo setting info...

Posted by SkyCadet | Jan 29, 2013 @ 11:48 PM | 4,809 Views
Taking the mystery out of expo settings on radios --- finally!

Did you ever wonder what those functions actually were that set the "expo" for your radios? Well, wonder no longer!

These are actually CUBIC functions that are symmetrical about the y-axis (relative throw) and are designed to either reduce or enhance response up to full throws.

After some digging, here is the formula!!!

y = rx³ + (1-r)x

Where:
x = control throw (stick position) amount. -1<x<1 for most radios;
r = the exponential rate setting in decimal equivalent of %.
(so for example, 25% expo = 0.25, and x = ±1.00 for full stick movement)

I have verified this result with two sources: One on the net, and another with software - Real Flight expos do the same on expo rates on models.

So, what does this really mean? The higher the expo, (above zero), the more dead band we find in the center of the stick positions - this IS useful to linearize a model's deflection of control surfaces. Did you think that throws are linear? Nope, not quite. The SERVOS are, in angle versus input from the sticks, but the movement is actually the SINE of the angle. I have some data below that illustrates what the relative motions of the surfaces behave for three angles: ±45°, ±60°, and ±75°.

±60 degrees is the normal throws at 100% for most servos. 75° is a 125% setting on control throws, and 45° is at the 75% throw rate.

The reason this is important to consider is that...Continue Reading

# Friend's DX7s backlight mod complete too!!

Posted by SkyCadet | Jan 09, 2013 @ 03:05 AM | 5,797 Views
My buddy ordered a backlight 9X kit the same time as mine, but he had not been in town until today. He brought by his DX7s (also requiring a backlight) and we installed it today!

It turned out superbly! See pix below. same basic deal as the DX6i, except the power is tapped off the positive lead off the vibration motor (to pin 2, the outermost pin on the connector left, fifth from the black lead on the 9X's connector plug) and the negative goes to the furthest right pin on the back of the radio (rear half board) (to pin 3, the innermost remaining lead).

See helifreak's DX7s backlight mod. (google it). Also, I left the heat shrink on his 9X connector, whereas for some unknown reason, HF took his off.

His install also made a slightly brighter white screen on the right side. I avoided this by using thin 1/16" foam double sticky tape on the board, and then the panel stuck to it. I then epoxied the main display edges (like I did on my Dx6i) to the panel, and added some foam sticky material that came with the 9X kit (~3/8" wide) on the exposed remainder of the panel that is past the right side of the screen (like I did with the 6i mod below). this acted like a spacer to avoid screen damage, and also hides the uncovered bare panel from creating inner reflections leading to a brighter right side (see HF's pix). Ours turned out perfectly!

Also used a Radio shack 4xAA flat AA holder with a cordless phone plug to allow either the stock NiMH pack OR 4xAA (NiMH or Alkaline) to be used in the TX! See pic below. Removal of the foam inserts allows a clean fit to this mod!
**make sure to reverse polarity on the plug - Spektrum has theirs opposite for some reason!

# DX6i Backlight mod done!

Posted by SkyCadet | Jan 05, 2013 @ 01:19 AM | 6,316 Views

Can you tell I am happy?

Finally! I love my DX6i, but reading the display and not having the ability to read it under sunny days well, or at dusk, really sucked!

I have some photos of the 9X backlight kit I got from HobbyKing. These are \$5, and well worth the \$\$. My DX6i is a great radio, and having used it with many of my models, I wonder why Spektrum left a backlight off the unit in the first place! The 6i TX is sometimes all one needs to fly a 4-5ch plane.

Took about 30 minutes total. I had to epoxy my display due to the issues with solder tails left too high on the circuit board preventing the use of hot glue easily or double-sided sticky foam tape. As you can see in the photo below, the display is crisp and clean - finally! Spektrum better start to add this as a feature in ALL radios moving forward. No excuses.

Notice I also added a swiveled extension for balancing the radio better using my neck strap, and wider thumb stix. both work well, got them off eBay.

 DX6i Backlight install using the \$5 Turnigy 9X Kit (18 min 35 sec)

This video is 18 min long, and the fellow does an excellent job of showing how to do this mod. not hard, and only one solder position to make work!! I highly recommend this. All one does is to remove the jumpers off the bottom display board, pull off the TX module, remove the display and put the 9x display under the glass display. Affix however you can, and BINGO!