Motor Math and Propeller Basics

A couple of nice articles which were pointed out by Superfly maven Tram.  It looks like there's a lot more interesting things there as well.

• Propeller Basics
• Motor Math

Elevon / V-Tail Mixing Calculations

update: moved this into its own post.  original elevon description here.

Calculating Elevon Motion

There are two calculations, one for each elevon:

        a = x/2 - y/2
        b = x/2 + y/2

where

•  a = left elevon deflection,
•  b = right elevon deflection,
•  x = aileron position (-1 = far left, 0 = centered, 1 = far right),
•  y = elevator position (likewise, -1 .. 1)

Deriving the Elevon Calculation

I couldn't find the above formula anywhere on the web, probably because it's so obvious to everybody but me.  Here's how I figured it out.  Real mathematicians would do it much easier I'm sure!

First, look at the inputs and outputs.  The above video shows the endpoints and midpoints of the two axes.

which gives us this table for the values of A and B:

    a,b = f(x,y):
                 x=-1.0       x=0.0         x=1.0
        y=1.0    -1.0, 0.0    -0.5, -0.5    0.0, -1.0
        y=0.0    -0.5, 0.5     0.0,  0.0    0.5, -0.5
        y=-1.0    0.0, 1.0     0.5,  0.5    1.0,  0.0

Showing only the values for A, we notice that there's a pattern across the rows, namely that it increments by .5 each row, as X varies from -1 to 1.  So, we can start with "+ x/2" for each of the rows, for some value of Y.

    a = f(x,y):
        -1.0    -0.5    0.0
        -0.5     0.0    0.5
         0.0     0.5    1.0

Likewise, we can see the same pattern for the columns in the other direction.  Fiddling a bit, I came up with -y/2 + x/2 which of course simplifies to x/2 - y/2.  I guessed there was a similar pattern for B, and tried a few variations of adding and subtracting x/2 and y/2. until I confirmed that x/2 + y/2 worked.

Here's a bit of python that reproduces the table above:

    for x in (-1.0, 0.0, 1.0):
        for y in (1.0, 0.0, -1.0):
            a = x/2 - y/2
            b = x/2 + y/2
            print a,
            print b,'\t\t',
        print

Notes on prop pitch

Great write-up by Gordon Johnson:

http://www.rcgroups.com/forums/showpost.php?p=16189250&postcount=4

Simply Brilliant Hot Wire Cutter Power Supply

From user 7up on rcgroups.  Power from a 3-5A 12V wall wart, managed by a 6-10A brushed ESC, controlled by a servo tester.  Attach the hotwire to the motor wires.

A nice explanation of PPM radio signals

http://www.mftech.de/ppm_en.htm

Interestingly, the radio transmitter and receiverr does no transformation of the signal between the encoder and the servo.

RC receiver to digital output converter

One tiny piece, not too expensive.

Kline-Fogelman airfoil thread

Here's the official RCGroups discussion thread for the Kline-Fogelman airfoil.  With contributions by Dick Kline!

TxDuino -- controlling a Futaba transmitter via PC

Controlling a transmitter via PC.

PC -> USB -> Arduino -> PPM -> Futaba module -> receiver.

The TxDuino project aims to create a single device that allows a PC to control an RC vehicle. At the time of starting this project, the only option for doing this was a device from here that could be plugged into the trainer port of a transmitter. An arduino has been used to achieve this same setup as described here. Going through the handheld transmitter, however, is a huge hassle for a number of reasons so I set out to create a simple single device that could accomplish this. As it turns out, so did the guys at Tom’s RC, their solution being this guy here. Anyway, since the work is done, I’ll share the results.

http://cheshirekow.com/blog/?p=236

Controlling Servos

Some servo-related linkage...

• Generating PWM signals using Timers in the ATMega chip
• Servo Basics
• Servo Design Basics 

Bonus:

• Electric Motors 101 -- DC, AC, brushless, servo, stepper, more...

HobbyKing Orange Micro DSM2 Receiver

HobbyKing RA61E DSM2-compatible Park Flyer Receivers arrived! (link updated to the Orange Micro variant)

• no instructions included (therefore, this post!)
• no problem with binding.
• works well.
• added 1.5" heatshrink myself.
• Pin assignment are the same as the AR6110e.
• Wire attachments are OPPOSITE the AR6110e. Control line is on the TOP.

Top photo is the  heatshrinked one, bottom has yet to be heatshrinked. Shown with Spektrum AR6110e for refererence.

Two chips on board:

• left chip is covered with glue, anybody know what it is?
• right chip is Cypress Semi CY8C21434 (datasheet).

How to replace a bind plug?

Freechip provides the answer:

If you have old servo leads or old servo extensions you can use these, strip and twist the 2 outer wires on the 3 wire lead and short them together.

The bind plug shorts the outer 2 pins on the BATT/BND port.

If you have a helping hand you can also use small needles nose pliers you can use them to short the 2 outer pins.

DSM2 specification details

• Protocol disassembly notes.
• Notes on USB control of DSM2.