Tuning for auto-level – MWC Quad
According to the instructions on multiwiicopter.com the mid and endpoints need to be set properly to ensure auto-level works properly. I hadn't bothered much with this except to make sure the throttle travel was low enough to arm the PARIS board. This is probably why I've spent so much time stuffing around with trimming flights trying to get the perfect autolevel hover. After so many trimming flights, I thought it would be good to go back to basics and start from the ground up. Especially since I've just finished assembly of the new Scarab Quadcopter, now is a good time to get things right.
Setting the low point to 1095, the midpoint to 1500 and the high point to 1905 is achieved via sub trim and end point adjustment (on my Futaba 10CAP). The first step is to get the midpoint right at 1500. For this example, I'll assume a working connection between your PC running Multiwiiconf software and the Paris board.
- Center all the transmitter sticks and trims.
- Read the values from the MWC software. They should be close to 1500.
- On the Futaba 10CAP, hold down MODE, then Sub Trim and adjust all 4 channels to as close as possible to 1500.
- Then use the END POINT function on all four channels to high and low point to 1905 and 1095 respectively. Using the elevator as an example, pull full back on the elevator stick and read the value in the MWC software. Hold the stick there while adjusting END POINT so the readout shows 1095. The push the elevator stick on the tx to the other extreme and use END POINT to adjust the readout in MWC to 1905.
- Repeat the process for the other three channels.
- Go fly and see what happens. In my case I'm getting a bit too much oscillation when I activate auto-level that I'm sure can be solved with some PID tuning. I also seem to get the occasional glitch where it seems two motors drop RPM just enough to cause a small drop in altitude. I'm not sure if it's actually a drop in RPM or vibration as I reckon I can perceive a slight amount of vibration. Come to think of it, those two booms are the ones missing one of the four screws in the boom holder because the shafts thread was stripped or non-existent. I do have two spares that came with the kit so it looks like I'll have to go back, disassemble and replace those shafts.
MWC Quadcopter – Cramming in the ESCs
These photos show the frame starting to come together. The bottom of the CF plate shows each of the four ESCs are held in place by 2mm cable ties. There's not a lot of room left on the top of the board after the ESCs and power distribution cable is laid down. On top of this will come the three leads from each motor to plug into the ESC. If you were thinking of using any gauge wire heavier than 20AWG, you might want to think again because even just space will become an issue.
The next plate above is prepared with nylon mounts to host both the MWC control board and above that will be another quad frame plate that is likely to host my GoPro camera. I haven't decided yet whether to put the camera up on the top plate or out in front on an extended arm. Up top under a dome would be better balanced and protected, but out on the arm might have a better view clear of the props. Undoubtedly I'll end up trying both but seeing as I don't have the extended arm, and it costs more money, I'll see how it goes up top first.
QuadCopter SCARAB – Motor Mount Retainer
These photos show the retaining screw cut to 7mm and how it penetrates one quadrant of the 12mm aluminium tube divided up by the motor mount. Cut to the right length, it doesn't intrude far enough to cause concern with rubbing on the wire from the ESC to the motor which is routed internally along the tube.
QuadCopter SCARAB 12 – Assembly part 2
The frame looks well laid out, light weight and just plain good looking. 20AWG is used to connect to the 2213N 800Kv Brushless Motors with just enough left hanging out the end to connect the four speed controllers ( TURNIGY Plush 12amp (2A BEC) BESC ). The only thing I'm unsure about so far is the sorta sharp edges of the aluminium booms and how that might rub against the wires.
Connecting the BMP085 Baro to the MultiWiicopter Paris V4
The BMP085 Barometric Pressure sensor is mounted on the bottom side of the Paris V4 board. Orientation of the BMP085 is not important but vibration is always an enemy so I used double sided foam tape to mount it. There are four points from the BMP085 that must be connected, VCC, GND, SDA and SCL. In this case they're connected to the LV I2C pads on the bottom side of board to the same points that the BMA180 Acceleromter is connected to on the top
Yellow wire is SCL. White wire is SDA. Red VCC and Black GND.
Paris MultiWiiCopter V4.0 board
Hooking up the components of the Paris MultiWiiCopter V4.0 board is a pretty straightforward job so if I can offer any advice, take your time and make sure not to miss any pins like I did. After making a concerted effort to have neat wiring and solder joints between the Arduino Pro Mini, the Wii Motion Plus, the BMA180 accelerometer and the BMP085 Pressure sensor, I found I wasn't getting any output from the sensors in the MultiWiiConf software. After deconstructing the board sensor by sensor, I found pins A4 and A5 from the Arduino board to the Paris board had been missed so effectively they weren't connected to anything. Now those particular pins are pretty important (well I guess most pins on the Arduino are pretty important to connect) as they take the input from the sensors! They're labelled as SDA and SCL and carry all the important stuff from the gyro, accel and baro sensor as input to the Arduino.
If you're familiar with the layout of an Arduino, you can see in the photo below the two pads in question missing any connecting pins. After soldering up these pins, everything worked fine.
*August 2011- Some more info on hooking up the baro sensor (http://fangin.com/blog/2011/07/26/connecting-the-bmp085-baro-to-paris-v4/)
*9th October 2011 - Added two pictures to show the connection between the BMA180 SDI Pin (#7) to the SDA connection on the Paris board.
*23rd December 2012 - Added a picture showing that I soldered the DC Bus closed. The advantage of leaving it open is to prevent noise entering the CPU and sensor section, the downside is a seperate uBEC is required to power the ESC / Servo side.
Troubleshooting the new V4 board by connecting the output of the new WMP into the old (known working board).
How To Add Bluetooth to your MultiWiiCopter
For not much more than $10, a Bluetooth adaptor is a cheap and easy way to get in-flight real time feedback from the onboard sensors and allows quick and easy modification to PID values via the MultiWiiConf software. Here's how to do it.
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Buy a serial to bluetooth adaptor - "Serial Bluetooth RF Transceiver Module RS232 w/ Backplane Enable & State Pin". The one from goodluckbuy.com is simple and works fine with the Arduino.
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Connect the USB FTDI adaptor to the BT adaptor. I used my breadboard wiring leads to hook up the pins in the following order.
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FTDI BT VCC VCC GND GND TXO RXD RXI TXD - Connect the FTDI USB Adaptor to a PC. The BT adaptor should now be powered with a blinking red led. Before using it with an Arduino running muliwii software, the baud rate of the BT adaptor has to be changed to 115200 from the default 9600. Now this is the part that stumped me for ages and sent me off looking up forums, updating bluetooth stacks etc etc until I figured out what I was doing wrong. To configure the BT adaptor, you need it physically connected to the PC via the FTDI USB adaptor but you don't want to connect the PC to the BT adaptor .... yet. The BT adaptor can only be configured when it's in an un-connected state. In your "Bluetooth Places" you should be able to see the device (by default called "Linvor") but it should show "not connected") and the red light should be flashing on the BT adaptor.
- I used Advanced Serial Port Terminal to connect to FTDI USB. The AT commands must be copy and pasted to send to the device because it constantly polls and if you can't type fast enough to complete a command before it reads it in.
- Send the "AT" command. BT responds with "OK"
- Send "AT+NAMEMultiWiiCopter" to change the default from Linvor.
- Send "AT+BAUD8" to change the Baud rate to 115200.
- Now connect to the Arduino as per the connections in the table above.
- Run the MultiWiiConf software and choose the BT COM port.
- Now you can fly around and see the gyro and accelerometer inputs change while in flight!
I found a page with quite a lot of detailed information on the BT adaptor during my searches. While it's native language looks Chinese, the Google Chrome browser seems to do a pretty good job translating it.
Quadcopter specs / parts list
The frame as shown with just the motors and plastic housing weighs 780 grams / 27.4 ounces. Maybe it's getting a bit on the heavy side with 24.5 mm aluminium frames but the aim for this one is primarily rugged and simple. If it does turn out to heavy and flight time is severely restricted, aluminium tubes half the size would do the job. Why not use them in the first place? Aesthetics was part of it as the fully enclosed 24mm frames might let me hide some wires and speed controllers to make it look more tidy.
The motors are 520mm apart which is probably the minimum separation for motors / equipment of this size - see the tips here on setting up and general rules of thumb for quads.
Parts List:
2 x CONNECT-IT Aluminium 600mm lengths: $5.81 each.
1 x 6 way joiner $2.24.
4 x End Caps: $0.49.
1 x Food container with clip on lid $3.36.
4 x 2830-14 750KV Outrunner Brushless Motor inc Mounts & prop adaptor: $9.99 each.
2 x 1 Pair 10x4.5" EPP1045 Counter Rotating Propellers: $3.49 each.
2 x New Styles 10 Pair 3.5mm Gold Plated Connector N3.5: $4.99 each.
4 x Turnigy Plush 30 Amp Speed Controller: $11.54 each
1 x warthox FPV/180_LLC - MultiWiiCopter board - v2.0 Plug-n-Play: $158