Sunday, April 15, 2012

[Quadcopter] Build Log and How To Guide

The goal of this guide is to provide a RC noob a tutorial on how to build a fairly standard quadcopter (not quite there yet :)).

So, what is a quadcopter? Wikipedia says: "A quadcopter is a multicopter that is lifted and propelled by four rotors. Quadrotors are classified as rotorcraft, as opposed to fixed-wing aircraft, because their lift is generated by a set of revolving propellers. Unlike most helicopters, quadrotors generally use symmetrically pitched blades; these can be adjusted as a group, a property known as 'collective'. Control of vehicle motion is achieved by altering the rotation rate of one or more rotor discs, thereby changing its torque load and thrust/lift characteristics." Well, that sounds funny, what does it actually look like?

In this picture, you can easily see all the important parts of the quadcopter. The most obvious things are probably the motors and propellers. The motors spin around at a few thousand RPM and so as the props spin with the motors they produce thrust. Here are some typical motors and props:
Next you'll probably notice the frame. This is commonly wood, aluminum, carbon fiber or glass fiber and has some sort of center plate on which 4 arms are attached. On the ends of these arms, are the motors. Here are some common frames:

In the center of the frame is the flight controller, receiver and battery. Flight controller is connected to all of the motors, and the receiver. It controls the direction, height, and speed etc of the quadcopter, by, as wiki said, varying the RPMs of the motors (and therefor the amount of thrust). A picture of a FC (there are MANY different types of FCs): 

Mounted on the arms between the motors and the center plate, you can see the motor controllers (called an ESC (electronic speed controller)) It is connected to the FC, battery, and motor. The three red wires at the top are connect to the motor and the red/black wires at the bottom go to the battery. The black three pin connector in the upper left of the pic below is connected to the FC so that the ESC can be controlled (and therefor the motor too).

The receiver connects to the FC and receives the signals from the transmitter that control the quadcopter. It has multiple channels for the different control inputs of the quadcopter:

The battery is a LiPo which has a higher power to weight ratio compared to a NiMH battery, for example.

A common TX is the second image below. In the first picture you can see the most important part of the TX; the "sticks". There are two sticks, and each can move left/right/up/down. These sticks control 4 different channels: rudder, throttle, aileron, elevator. These are based on airplane controls, but still make sense for a quadcopter. Rudder controls the Z axis of the quad, yaw, or spinning without moving left/right/forward/back etc. Throttle controls the RPM of the motors and thus making it go higher/move faster. Aileron is Y, roll, or tilting left/right. Elevator is X, pitch, or tilting forward/back.  There are two main "modes" of a TX; mode 1 has the throttle stick on the right and ailerons on the left, and mode 2 is the opposite.

To build a quad you basically need:
4x motors
4x ESCs
4x Props (2 CW and 2 CCW)
1x LiPo battery monitor
1x Frame
1x FC
1x TX/RX
1x Battery Charger
1x Battery (extras are good)
HobbyKing (to buy stuff)
RCGroups (help!)

Starting from scratch, the frame is probably the first thing to pick as its design/size depends on what you want to do and changes the rest of the build. 400mm to 700mm motor to motor fairly standard for most quads. Most times beginners build their frames out of aluminum or wood. More expensive(most times better) are made of carbon fiber. For your first quad, though, it'd be better to but a pre-fabricated frame. HobbyKing is now really starting to get into the quadcopter stuff and has quite a selection of frames now. But, whatever you do, don't buy one of those 10$ cheap wood frames as they break very easily. The rest of the frames there do look ok, but the motor mounts on the Talon style frames are a bit weak; you can get some better ones off ebay. HK is not the only place, though, google will find you hundreds of frames. Dialfonzo, from the RCgroups forums, also has some nice frames.

DIY Frames
This image shows the parts that a frame requires:

A wood frame is probably the easiest for a beginner to DIY frames because wood is a easy material to work with. 3/8in to 3/4in square poplar or hardwood is what i have seen the most, but i think 3/8 is a bit to flexible and as i saw at the Home Depot, severely twisted. But, I found some nice 1/2in hardwood that wasn't twisted very much and it has worked fairly well. On any type of frame i still like to use two CF plates with the four arms squished between to create a X or + shape. The next important thing is how it's mounted. Currently, my wood arms have two holes in them spaced .75in apart with bolts going though it and the CF; I'm guessing that it will also crack down the center like the crappy CF square tube that HK sells, so, i recommend to use something that squeezes the arms between the center plates and not bolt into the arms. You can probably get away with mounting the motors directly to the arms if you extend the ends of the arms past the prop so that the props cant hit the ground in a crash.
This my favorite option and is very popular because it is easily accessible, fairly light, and strong: typically, 3/8 to 1in in square tube/tube is used. A good thing to note is the wall thickness of the tube; you want pretty much the thinnest you can get, otherwise the weight is too much most times. 1.64in or 1mm is good. Regular tubes are stronger than square tubes of the same specs. With Aluminum you can, with fewer issues, bolt the arms directly to the center plates, and the motors to the arms, unlike CF and wood.
Carbon Fiber
If you are going for CF, make sure you get the proper cross-weaved stuff. Even then, it'd be better not to drill into it; instead use clamping type mechanisms to hold the arms into the base and the motors onto the arms. If you get the CF square tube from HK which only has CF going one direction and you drill into it for the mounts, it will fail. Again, square tube would be better because it is not circular(of course haha) and you will know for sure that the motor are on straight.

Motors + Props
These two are inevitably intertwined (along with pretty much everything else in a quad) and greatly depend on what you want to do with your quad. Most times a frame will give recommendations for motors and props. Generally, the bigger the quad, the lower the Kv (how fast the bladed spins, stands for rpm/volt) and the bigger the prop. Smaller quads have a higher Kv (blade spins faster) and smaller props. This is because the quad doesn't have room for the bigger props, so it must use a higher Kv to achieve sufficient thrust. With bigger props, you have slower reaction times, but more stability. For choosing a motor, i would pick the props first. You will want to choose the biggest(most times) that will fit on your quad with at least few inches between the FC and other props. But, you can also spread the motors out even more for better stability, generally. Once you find the props, find a motor that can spin them with efficiency and a good amount of thrust. The total weight of your quad should be about 1/3 of the total motor thrust (2/3rds, for good measure, of 1/2 of the total thrust). is a great place to look at for thrust data, and Google also works pretty well too. 700 to 800Kv is good for 11in props, 900 to about 1100kv is10in props, 1200 to 1300kv or so use 9in props, and so on. eCalc does a very good job at getting you in the ball park of how your quad will perform. The calculated hover throttle needs to be 50% or less. Oh, and, thrust depends on the voltage the motor is receiving. The higher the voltage, the higher the amperage/thrust/Kv, but the motor might not be able to handle that. All motors have a rating, its better not to go over it. Commonly, multirotors will be 11.1v or 3s. It is also very helpful to look at other people designs and how well they work. 

This is probably one of the easiest things to pick out. These controls the motors depending on what signal the FC sends. After you've found your motors and how much current they're going to draw with the props you choose, you can choose the ESC. If one of your motors draws 18amps at full throttle, you wouldn't want a 18A ESC beacuse that would put a lot of stress on the ESC. Instead you would want to get a 25A ESC or even 30A. You should also get one that has a fast refresh rate; 400hz is really good and the Turnigy Plush/Basic are some of the most used on quads. Also pay attention to the voltage rating. 

This may seem daunting to a beginner to pick out and may result in bad things if chosen incorrectly, but with a few tips it is quite easy to decide. First thing to consider is weight; it will most likely be the heaviest thing on your quad. If your battery is too heavy, it can badly affect your quad, and weight pretty much always is directly related to capacity. Since you know that your AUW should be about 1/3 of the total thrust of the motors and so the battery should be the last thing you pick to get to this total weight. Make sure you pick a 3s battery, for example, if you have 3s motors/ESCs.

Next thing to look at is amp draw. If you have four motors that draw 18A each, that's 72 amps total, and a 2200mah battery fits your weight and run time requirement, you would need at least a 32C battery as 2200mah = 2.2Ah and 72total amp draw divided by 2.2Ah is 32.7C (aka total amp draw divided by battery capacity in Amp hour). Again, like the ESCs, higher is better, so, maybe 45C? Continuing with that, lets find the flight time. (2.2Ah / 72A) * 60 = 1.88min. the equation is: (battery capacity in Amp hour divided by total amp draw) times 60. Those were calculations at 100% throttle. You can just use eCalc for most calculations, anyway.

if your quad weighs 1kg and your motors supply 4kg in total(1kg each) at max throttle. and the total amp draw is 72A. the hover amperage would be 72/4(the quad is 1/4th of the motor thrust) which is 18A hover thrust. so doing the flight time calculation again: (2.2Ah / 18A) * 60 = 7.33min hover time.

This (the flight controller) greatly depends on your tastes; Arduino based such as MultiWii works for most people but it requires some tinkering to get working and is great after that. KK boards are very cheap, gyro only, and fairly typical for beginners. SM32 based FCs are more powerful and work a little better accordingly and are MultiWii compatible such as TimeCop's Free Flight board. But, for most people the additional processing power of STM32 doesn't really make a difference. Then there is the NAZA and Wookong which are the best for minimal setup required, besides RTF, of course.

Here are my specs:
Custom frame - aluminum arms/CF plate 
Pololu MinIMU9-- L3G4200D Gyro, LSM303Accelerometer/Compass

I started out with the motors first. I had to do a few things to get them working for my particular build: put the propeller and base mounts on, cut off axles on the bottom, and put the bullet connectors and heat shrink on.

I dumped all the extra parts from the motors into a little container so I could find the stuff easier.

Cut off axle with air powered dremel.

Prop mount and bolts

A little locktite to keep the bolts in.

All the prop mounts done.

All done with bullet connectors and heatshrink!

As you can see in the last image, these ESCs need to be connected in parallel with the battery. then the three red wires go to the motor. If the motor spins the wrong way, switch any two of the three red wires.
Soldered on bullet connectors

All done.

ESCs soldered together in parallel "spider" arrangement with XT60 connector. I soldered the ESCs together semi-permanently, but some may like bullet/XT60/etc connectors so that repairs are easier.

Custom Frame

This uses a 1.5mm CF center plate with four aluminum square tubes with holes drilled in them. I also took off the X motor mounts and mounted the motor directly to the arm which is way better and stronger. I  have found that aluminum is the only material that i will drill holes into as wood and CF will crack, so, aluminum is my new favorite build material until i can get some proper boom/motor mounts for CF. The 4in PVC landing gear are awesome and were made of 3/8in wide pieces cut off of a 4in piece of pipe for each arm.

I was testing the BLHeli silabs firmware, sot that why there is not heatshrink on the ESCs in these pics.

The battery came with bullet connectors, but i planned on using XT60 connectors. The charger also used the XT60 connector.
Original battery

The wires got a little close...

All done

Before cahrging any sort of LiPo, its good to know some background; They do explode! Also, read through this post at RCGroups forum. It gives a general overview of LiPos, how to charge them, and not make them blow up. :)
ATX PSU used to power charger using the included cables. Balance and main charge connectors from the battery are connected to the charger

When first turned on, the charger looks like this. 

If LiPo is not already selected(see previous image), press the Type button until the correct battery is selected, then press Enter.

Then it will look like this. Press "+" to go to LiPo Balance and then press Enter to select/loop through the charge settings, then "+" and "-" to change values. When ready to charge, press and hold the Enter button. Then Enter to confirm. After Charging has begun, press "+" to see individual cell voltage.

Connecting the FC!
The standard MWC board has four common areas: Power in , RX in, sensor hook ups, and ESC outputs. Lets use the MWC SE Lite board as an example.You will hopefully find some sort of diagram for any board you buy from the place you bought it.
With this board, like most others, the power is supplied through one of the ESC outputs(bottom center, labeled M1-M6) through the ESCs internal BEC(a most times 5v power supply). So if you plug in a ESC with a 5v BEC, you got power! Also, you should check what voltage the BEC is and what voltage your board needs--they must be the same.

RX channels
This is really simple; just get some male to male servo cables and connect throttle from the RX to the throttle on the FC. Do the same for all the other channels. All MWC boards will have one AUX channel for selecting between level/acro, but the MWC SE and many other boards have two. The 5v from ESC goes through to the FC and then is sent to the RX through the cables that link the RX and FC.
(RX Channel), FC Pin
Throttle           2
Roll                 4
Pitch               5
Yaw               6
Aux 1             7
Aux 2             12

Note: if your RX supports PPM Sum (outputs all the channels onto one pin), you can plug that into pin 2 (throttle) and have all the other pins open for other stuff.

The MWC SE has the sensors built in to the board, so you don't have to work about adding them. Most IMUs that can be bought now have internal level shifters (because most IMUs are 3.3v and most FCs are 5v) and pullup resistors which make it 5v compatible. So, if you have one of these, you can just connect SDA to SDA, SCL to SCL, GND to GND, and 5v to Vcc in on the IMU and your done. Here is a thread by me that shows a few more IMUs.

ESC outputs
-simply plug the servo connector from the ESCs to the motor ports. Check to make sure you have the ESC in the correct port for its place on the quad, look here under Connecting Motors and Servos for what ESCs go to what port.
-Something worth mentioning is that there are two types of BECs: Switching and Linear. If you have ESCs with a switching BEC, you MUST remove the red(+5v) wire coming from all but one ESC. If you dont, your ESCs(specifically, the BEC inside) will get VERY hot. If you have linear BECs, you dont have to remove the red wire, but most people still do.

The MWC boards use a serial interface to program and to adjust settings in the GUI. Most times a FTDI adapter is used.

TX Setup
Using the standard firmware that comes with the 9x, a few settings need to be changed for multiwii compatibility. Here is the instruction manual.
1. The sticks need to be set to Mode 2. (Menu/Sys Settings/Stick Set)
2. The TX should be in ACRO mode. (Menu/System Settings/Type)
3. You need to enable ch5, maybe ch6, and assign them to the switches so that you can switch between Accel/Gyro etc in flight. (Menu\Func\Aux-Ch)
4. It's not required, but you can calibrate the sticks value range:
-Push the right lower trim tab to the left (aileron on a mode 2 TX), and the left side trim tab up (Throttle trim on a mode 2 tx), and while holding them, turn the Tx on. 
You will get a screen that shows the version number of the firmware, with four zeroes (0000) at the top of the screen. 
-Center both sticks in their range in all axis, and press the menu button until it beeps and release. The screen number will change to 0001.
-Move the right stick to the upper right corner, and press menu, and you should get a beep, and the number on the screen will change to 0002. 
-Put the right stick in the lower left corner, and press menu, and get a beep, and the number will change to 0003.
-Release the right stick, and put the left stick in the upper right corner, and press menu, get the beep, and the number will change to 0004. 
-Put the left stick in the lower left corner, and press menu again, get the beep and the number will change to 0005.
-Center both sticks, and press menu, get the beep. You are done calibrating the sticks.
5. Some also say you need to set the ATV/servo range settings (Menu\Func\E. Trim):
pitch (elevator): 50% 
roll (aileron): 50%
yaw (rudder): 100%
Initial gain pot values is 50%. Increase until it starts to oscillate rapidly, then back of until it is stable again. Fast forward flight needs lower gain. But I found mine to work just fine at 100%.

5. You can find the "DISPLAY" option in the Func menu, and that will display the values of the sticks so you know it is working.
6. Here is how to use the sticks on the TX to arm/disarm etc the quad with multiwii v2.0:

MWC GUI/more TX Setup
Basic MWC code config
-First, you need to get the latest MultiWii code and the latest Arduino IDE. Once you have the code open and have the config.h tab selected, you need to uncomment the orientation your quad will be in(QUADP, QUADX etc) under "The type of multicopter". Right below "type of multicopter", change I2C speed and I2C pullups if need be for your sensors. Then scroll down a bit until you find some #define lines for the gyro, acc, and mag. Like before uncomment the sensors you have or uncomment a board if yours is there. You could also search for RCAUXPIN and change that if you have a second auxiliary channel.

-If you have a ITG3200 or MPU6050 gyro, go to the Low pass filter setting section and un comment the 42Hz filter for your gyro. This can significantly stabilize your quad. I have the L3G4200D gyro which doesnt have LPF settings built into the code, but i found this post which has some code for my gyro that goes in the sensor tab of the code. Just find the old code and paste over it with the new code. But the best fix for reducing vibrations etc, is to fix it at the source--balance motors, props and get some good anti-vibration padding for the FC.

-#define MINTHROTTLE When you arm your quad, this is the value that is sent to the ESCs. it should be a little below the value that makes the motors spin up. This should be a little bit less than the min value of your throttle channel, aka,1095.
-#define MAXTHROTTLE This is the max value of the ESCs(aka full power); when the throttle stick is all the way up, this value is sent to the ESCs. Should be the max value of your throttle channel, AKA, 1905.
-#define MINCOMMAND is the value sent to the ESCs when disarmed. This should be below the minimum throttle, AKA 1095.

Setting up TX Channels in the GUI
-There are two main things we need to look at for now: transmitter channel values and the sensor data. First make sure the quad is disarmed and move all the sticks to their center positions. Now look at the TX channel values; they should all be around 1500 when centered. If not, go to your TX function menu and look for subtrim. Subtrim allows you to change where the center point is of the channels, so change the subtrim for each channel so that the values are at 1500. Then move each stick to its lower limit; it should be near 1095. If not, go to E. point in the function menu and change the percentages for each channel to change how low or high the channel value goes. If you move the selector to RUD(aka yaw), for example, you can move the yaw stick from side to side to select the high and low range value percentage. Use + and - to change the value. Do the same for each stick except for the upper limit of the channel value range; it should be 1905. Now all channels should have a midpoint of 1500 and lower limit of 1095 and a upper limit of 1905. If you cant for some reason change the center value of the TX channels, find the code #define MIDRC and change it to your center value. Also, if the channel values jump around a bit(jitter + or - a few) and cause minor drift, find #define DEADBAND and uncomment it to enable a deadband around the pitch/roll stick centers.

Check for Gyro Orientation
-Then click on the attitude meter so that it changes to pitch/roll indicators. Now, when you tilt your quad to the left, the roll line should tilt to the quad angle. Check the same for pitch(front/back tilting). If pitch/roll don't line up with the quad, then you'll need to change the GYRO_ORIENTATION part of the config code. It looks like this:
#define GYRO_ORIENTATION(X, Y, Z) {gyroADC[ROLL] = -Y; gyroADC[PITCH] =  X; gyroADC[YAW] = Z;} Specifically, if it rolls right when you tilt it left, -Y would become Y.
So, say pitch and roll are switched,  you need to change (X, Y, Z)  to (Y, X, Z). Y is pitch,  X is roll, and Z is Yaw. If roll was reversed(whwen you tilt the quad left, mw-wingui shows it tilting right, for example), you'd need to change gyroADC[ROLL] = -Y to gyroADC[ROLL] = Y. Note the "-" sign.

-If your quad is "yawing" the wrong way find the #define YAW_DIRECTION 1 part and comment it out and uncomment the #define YAW_DIRECTION -1 line. If you push the yaw stick right the front of the multirotor should turn right

Check for Motor Rotation
Look here under Connecting Motors and Servos to find motor rotation(arrows around the motors) for all types of multirotors. If the motor is spinning the wrong way, switch any two wires (of the three going to the motor) and it will reverse direction. It also shows, as i said before, the port that the ESCs should be connected to on the FC(numbers in the motors).

ESC Setup--This is done after the TX channels are set to 1095/1500/1905.
To set the throttle range of the ESCs:
Do this for each ESC. You can also get/make a 1-4 adapter so you can program all of them at once.
1. Connect the ESC to the throttle channel of the receiver (In my case it was ch3). Make sure the motor is connected to the ESC, as it produces the diagnostic beeps, but no props on because a malfunction may cause a prop to go spinning around at 100% throttle...
2. Turn on the radio and put the throttle stick to maximum position
3. Now connect the ESC to the battery
4. The motor should do a 1 2 3 beep followed by two short beeps. Immediately after the two
short beeps, put the throttle stick down all the way, the motors should make 3 short beeps
(representing the 3 cells of the battery) and then finally make a 1 long beep, indicating that the
throttle range has been set (calibrated).

To configure the other ESC settings(this can be done before the TX channels are 1095/1500/1905, though):
There are two options here: a programming card or using "throttle stick programming". I somehow forgot to put the programming card in my shopping cart from the HK wish list, so, i had to use the second method. Its pretty similar to setting the throttle range until step 4.

1. Connect the ESC to the throttle channel of the receive (In my case it was ch3). Make sure the motor is connected to the ESC, as it produces the diagnostic beeps, but no props on because a malfunction may cause a prop to go spinning around at 100% throttle...
3. Now connect the ESC to the battery
4. Wait for a musical tune from the ESC
5. After the tone should be a sequence of beeps: setting after "(...)" is what it should be
    one short beep is the brake setting(off, on) off
    two short  beeps is battery type(Li-xx, Ni-xx) Ni-xx
    three short beeps is cut off type(Soft-Cut, Cut-off) Soft-Cut
    four short beeps is cut off voltage(Low, Med, High) Low
    one long is startup mode(Normal, Soft, Very Soft) Normal
    one long and a short beep is timing(Low, Med, High) Med is typical.
    one long and two short is factory reset
    two long beeps is end setup mode and resumes normal operation.
Then it plays the musical tone and loops through the beeps again.
6. To select a setting to change, wait until right after the correct beep code(step 5), and then quickly bring the throttle stick down. This selects the setting.
7. Now, the ESC should beep a few times depending on how many options the particular setting has. To set the option(in parentheses in step 5), just move the throttle stick back up immediately after the correct option beep. The ESC will then continue with the sequence of beeps until it is unconnected or the "exit setup" setting is selected.
That was probably confusing, watch this video instead. :)

Now that everything else is done put the props on. You probably cant tell, but i have the props on upside down in the picture below of my first build. For some reason when i was putting them on, i didn't pay attention to the shape(like an airfoil) and put them on upside down. Most times the writing(most times a brand name and prop size/pitch) is facing up.

This caused a lack of power( loss of 50%!), and yaw issues. Here are some pics to help with prop orientation. Motor rotation is shown by the arrows around the motors. 
This shows the direction that the motors need to spin!

Pusher/CW on front back, Tractor/CCW/ on left/right (for a "+" quad)

Before you Fly
Do general checks:
-Make sure all connections are tight
-TX in the right mode etc
-Nothing loose
-Do training in flight sim:
Follow this guide: HobbyKing Forums - How-to: Using your transmitter for simulator use. Make sure you turn on training mode( Menu/ Func/Trainer), and don't turn on the TX power when using it for the simulator as it seems to not work(will turn on automatically when the the audio cable is plugged in). That was how it worked at first, but then it stopped working and the power switch, along with the trainer switch, had to be on for it to work! Its so weird. After i got the er9x firmware on it, i have had no issues!

Post Setup "Stuff"
TX Mods
battery holder, trainer mode mod, er9x software mod
How to setup er9x for MWC

General Problems
ESC smokes: try switching the bad ESC with a working one to see if it is the ESC or motor(if the new ESC smokes, it is the motor and if the new ESC doesn't smoke, it was just a bad ESC) OR switch the motor with another known good one. if the ESC still smokes then it is the ESC, if it doesnt smoke again, it was the motor(touching phases), but that requires that the ESC works (the one that smoked).

PID Tuning
This will make your quad way more stable. I can guarantee that everyone's PID settings are different because all quads are slightly different in structure. Here are some guides until i figure out how to explain it:
Here are some short how-to statements:
P: This is probably the easiest. if the quad oscillates by shaking it or in flight, lower P. if it doesn't oscillate then increase P until it does and the decrease a bit until it is stable.
I: "An easy way I found to get the "I" value right.. I run up the motors while holding it above my head then pull back some pitch to tilt the quad up at the front, if it falls back level again then I will increase I until it just stays there.."
D: This is how fast the multirotor moved on the axis. if it is sluggish, increase D (remember, that means a LOWER number as it is a negative value). If you have oscillations you can either decrease D (remember, that means a HIGHER number as it is a negative value - i.e. further negative from zero)  or P.

"PID" Stand
This is a most times wooden stand that limits the quad to one axis of rotation(pitch or roll).  It limits the quad to one axis(roll or pitch) and is used to do PID tuning. Mine is quite simple; just a "+" shaped base with two support 2x4s that have some 1/2in PVC mounts for the quad arms.
After doing some more tuning, i find it easier to just go fly it after making changes rather than using this thing.

ESC Flashing
Flashing the ESCs with a after market will provide a much more stable multirotor. Check out the Atmel(by Britt) or the Silabs(by me) flashing guides at

Prop Balancing
This is quite simple too; a square base with two hard drive magnets mounted about 4in away from each other on some scrap wood. In the center is a simple piece of all thread ground to a point to reduce the friction on the one end that does touch the magnet(one end is floating, one is on the magnet).

To balance the props, find which side is heavier using the balancer and add some sticky tape to the tip of the leading edge of the lighter side. Some people also remove some material on the heavy side instead.

ACC Tuning
The ACC(accelerometer) keeps the quad at a constant level, except for pitch/roll stick input and then snaps back to level, and always needs trimming from default settings. You can do ACC trimming without a PID stand, it just probably harder. To trim the accelerometer so that it holds the quad level, do the following;
1. Put the quad into level mode with the Aux channel and attempt to lift off. It will most likely not lift-off level. Note which side(or sides) that lift of first.
2. Disable the motors(double check), and move the throttle to 100%.
3. If your right motor lifted off first, for example, you need to trim in that direction. So, move the roll stick to the right, hold it for about a second, and then bring it back to center. This is one "tick" and if you have a LED on your FC, you will see it blink for each tick.
4. This one tick may not be enough, so you need to arm the motors again and see if it is level. If not level, repeat #3.

Motor Rewinding
Rewinding a motor isn't that hard, just look at this site. You need to make sure you have the correct number of turns on each tooth, the correct termination(delta or wye), correct wire size, and the winding type(LRK,dLRK, ABC).
In my case:
The motor was originally 924kV, so from this picture i can tell that i need 12 turns and delta termination(delta because that's what the motor was when i took it apart). For wire size: the bigger the better, but you must still be able to fit all the windings on the teeth, and in my case someone said 25AWG would work. I went to a nearby 3E and got some 25AWG clear enameled magnet wire. The motor had 12 teeth and 14 magnet, so i had to use the dLRK winding method. Always wind the wire clockwise on the stator tooth(that is unless you're doing dLRK in which some are CCW).
Done can see the sharpie mark i used for marking a tooth as the starting point.

After thoughts...
Always double check your prop orientation--it can cause many issues if you think you have them on right when they aren't (guess how i know...).

Be nice to your motors! Don't put the props on upside down/too big of props and cause the to burn out. Some other motor alternatives for this size of quad are the: Turnigy 2217 16turnKD A22-20LA20-20L, KD 36-28SPark450(1200kv), or Turnigy D3530/14. The 22-20Ls would probably the most powerful of the bunch. flybrushless and ecalc are very helpful for finding the right prop.

Get a 2200mah 3s LiPo(or so) instead of a 4000mah like i did. The 2200 is about 40% of the weight and so you will get more agile flying, but less flight time. use the 4000mah for FPV etc.

A LiFe or a LiPo TX battery works much better than using inconsistent AAs and their battery holder.

I would recommend this IOI FC board for multiwii as it is even cheaper than my DIY FC solution was and has more sensors!

Hide the ESCs in the center of the frame as it looks so much nicer!

Unless you have access to a CNC or similar, it's a good idea not to build your first frame ;).

My (re)Builds
 I learned A LOT from this first build of my quad copter
- the arm mount/center hub idea didn't work to well, neither did the motor mounts.
- get some CF mounts for the arms (for center plate and motors) that don't put holes in the CF arms.
-still haven't really decided  on a battery holder on landing gear.
-pay attention to how you put the props on :D
-thoroughly research prop + amp draw.
-either buy a cheap(and awesome) bambu IOI FC, or make a FC on a PCB -- saves mounting hassle.

pics:  Look here to see the CAD drawing of it. It's quite simple with only four 10mm square CF tubes and some 1.5mm CF sheet.
I put some blue tape roughly where I needed to cut and then marked exactly where i needed with a pencil.

Done cutting

Again used blue tape so that i can mark my holes. Both pieces of CF are taped together so that the holes will line up perfectly.

 3/8in(10mm) "+" pencil colored shape is where the square tube would sit when assembled. Not perfectly lined up holes, but it worked out fine.

CF pieces will assemble to the blue highlighted CF piece. 

Motor mounted.


Second Build
Made a few changes:
-using pool noodles for landing gear
-props on correctly :P
-smaller battery; the 4000mah works pretty good too. the flights are really long :D
-drilled four holes into the arms so that i cant bolt it directly to the frame and motors (bad idea).
-FC a bit cleaner, still need to mount better.

Third Build
-Still using CF, but had dowel and guerrilla glue inserts- really strong!
-Real battery holder.
-Proper FC mount.
Dowel and guerrilla glue insert

 Hiding the power spider in between the CF plates this time!

 Looks much better.

Battery strap holder.

New proper FC mount.

Need to tie down motor wires, ESCs, and RX.

Fourth Build
-This is the current build and is in the build log section.