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Project #013 - RC Quad Copter - Page 3 - Pre-Build - Getting technical

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Article Index
Project #013 - RC Quad Copter
Page 2 - Pre-Build - Ordering the parts
Page 3 - Pre-Build - Getting technical
Page 4 - Pre-Build - Wiring
Page 5 - Construction - Motor mounts
Page 6 - Construction - Framework/Pod
Page 7 - Construction - Wiring
Page 8 - Flight systems testing
Page 9 - Night Flights
All Pages

GETTING TECHNICAL

Before I can start assembling the Quad-Copter I want to document much of the technical elements. Much of these details I have gleaned from RCGroups. This will no doubt be usefull to me when I first power up and start configuring the Quad.

RADIO Tx CHANNEL ASSIGNMENT
Channel 1 - Left/Right Stick, Rev Mode, 100% Epa, -50 Exp
Channel 2 - Up/Down Stick, Rev Mode, 100 Epa, -50 Exp
Channel 3 - Throttle, Rev Mode, 100 Epa
Channel 4 - Yaw, Norm Mode, 140 Epa, 0 Exp (or even +25)
Channel 5 - TI enable, Norm Mode (Thermal Intelligence on/off)
Channel 6 - TI sensitivity, Norm Mode (best to use an analogue channel, but digital will work using endpoints to set sensitivity)

Note: Set up Dual Rates on Ch.1 & 2 to 60%.

THERMAL INTELLIGENCE (TI SENSOR)
A range of 10% to 35% (Ch.6 of Tx) is considered reasonable. The higher the value the more self-levelling occurs.
When TI is on outdoors with two green LEDs, the self-leveling is very obvious.
You can't test TI by tilting the frame as your body's IR heat signature will mess up the TI, and the gyros themselves will respond to that as well.
To test TI, if you arm the quad with TI 'on' and set the sensitivity to where it is active, then, with the quad held tightly to the ground, put in a minimum throttle to get the motors spinning. Now hold your hand about 2 feet away from one sensor and slowly move it close to the sensor. You will notice the motors on that side speed up. This is a good way to individually test all the sensors.
If you get no response, check to see that your channel 5 gear switch is in the correct position to have TI on, and/or put in a bit more sensitivity with your channel 6 knob or flap lever and do the sensor hand check again.

TI checklist for outside flights:
1. TX on, throttle down, then PWB on *red LED will blink faster if throttle is moved up prior to arming indicating channel lock.
2. TI cal - Check for one or two green LEDs (preferably two green LEDs for good TI) when holding the Quad from behind, front pointed to the sky, bottom to ground. If one or two green LEDs are lit, TI flight is possible. Continue holding the Quad with front to sky and press the arming button for three seconds (insure that you are actually pressing it as there is no other indication other than the red light stops blinking and the tactile feel of it being depressed) *note 1: The green LEDs both will be on steady after this on the PWB V. The green LEDs both go off on the "experimental brushless PWB V TI"* **note 2: Do not calibrate TI over concrete/asphalt, cooler ground preferred**
3. Place the Quad on level ground, front pointing away from you.
4. Stand at least 15 feet to decrease the effect of your bodies IR image, then calibrate the TI level by moving the throttle stick down and to the right.
5. Stand behind the Quad slightly increase throttle to get props spinning, insure proper nick, roll and yaw stick response.
6. Bump throttle to 50% to get a low hover, note any trimming required to get a stable hover.
7. Land and hold the TX throttle stick full down and left, then press the arm button to set the loss of radio signal trims.
8. Fly! The battery low indication will flash the red and green LEDs simultaneously. The PWB will decrease the throttle response requiring more throttle to keep it airborne, so then land as soon as possible and recharge/replace the battery.

PRE-FLIGHT CHECKLIST
1. TX and Quad batteries fully charged.
2. TX on throttle down, then PWB on *red LED will blink faster if throttle is moved up prior to arming indicating channel lock.
3. TX throttle down and to the left (turns TI off) and hold, then press PWB arm switch. (The green LEDs both will be on steady after this on the PWB V. The green LEDs both go off on the "experimental brushless PWB V TI" )
4. Stand behind the Quad, slightly increase throttle to get props spinning, insure proper nick, roll and yaw stick response.
5. Bump throttle to 50% to get a low hover, note any trimming required to get a stable hover.
6. Fly! The battery low indication will flash the red and green LEDs simultaneously. The PWB will decrease the throttle response requiring more throttle to keep it airborne, so then land as soon as possible and recharge/replace the battery.

THROTTLE CALIBRATION
Throttle Calibration programs the ESCs for maximum performance with a particular system. The following procedure calibrates the ESCs for use with the Spectrolutions quad controller (PWB).
Note: It's debatable that throttle calibration is absolutely necessary, it's really down to what ESC's and motors that you use. If you decide not to do throttle calibration, then the only thing you may need to do is set your throttle max EPA up to say 120%.

Advantages of thottle calibration are:

- More power at maximum throttle
- Lower motor starting position on the throttle stick
- Larger range of joystick operation for smoother throttle control
- Better match of motor speeds among the four quad motors

Calibration procedure:-
1. Set Transmitter endpoints for Channel 3 throttle:
Upper Endpoint = 66%
Lower Endpoint = 95%
Also make sure that the trim and subtrim settings are at zero.
2. Remove Receiver from controller
3. Select one of the ESCs to calibrate and remove the servo connector plugged into the controller board. (Keep ESC power connector attached to the controller)
4. Plug the selected ESC servo connector into the receiver channel 3
5. Turn ON transmitter and set throttle to MAX postion
6. Connect battery to Quad system
7. Immediately after the tones from the ESCs stop, move throttle to MIN position. (You should hear another set of tones from the selected ESC.)
8. Disconnect battery from Quad system
Repeat steps 3 thru 8 for the three remaining ESCs
9. Set transmitter upper and lower endpoints back to 100%
10. (Optional) If you want the motors to start even quicker on the throttle adjust the subtrim to -50.

Note:-
If you use a couple of Y-cables you can hook up the 4off ESC's to Ch.3 of the receiver and do all 4off at the same time.

GYRO TESTING
A 'shake test' in each axis will enable the roll and pitch gyro potentiometers to be set correctly.
It is easiest to unplug two of the motors and do one axis at a time. Just turn the pot in the axis you are adjusting a tiny bit in one direction or another and then do a hard shake with TI off at 1/2 throttle (after throttle calibration has been done).
Keep doing this until there are no oscillations. It should only oscillate once or not at all after a very hard shake in that axis you are adjusting. If it gets worse move the pot in the other direction. There is a relatively small sweet spot that stops the oscillations that you will find.
Then do the same for the remaining axis. Leave the Yaw pot where the calibration mark is. You can mess with that one later if your motors and trim are proper and your heading is still not holding well.

Update:

For my own quad, I found I still never got any oscillations with all three pots set to maximum, so that's where I have left them.

The three pots are shown in this photo at the maximum setting (red dot). The original default seetings are thus that 1/2 setting for all three will be the desired setting for most people. Setting the pots below 1/2 setting will be good for small quad frames and higher than 1/2 setting will be good for larger frame quads.
Note: If you have something really extreme for the platform/motors, you can remove the three circled 51 K resistors and have an additional 2x gain range for the gyros.

ESC CONFIGURATION
For best results the Turnigy ESCs need a little tweaking in respect to the low-battery settings, i.e. it's best to disable the low-battery cut-off. Since there are 4off motors/ESCs then if the battery voltage does drop then it's more than likely that one of the ESCs will react before the others and the QuadCopter will flip. From experience, this can happen when coming down to land and the throttle is raised to level out prior to touchdown.

The default Turnigy settings are for a Lipo battery and a minimum voltage. However, if you set the battery type to Nimh then the minimum voltage can be set to zero.



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