TriWiiCopter: Connecting the brain
Today I disconnected the 4 HK401B Gyros from the three ESCs and 1 yaw control servo for the purpose of hooking up the new Arduino control board.
Tips:
1) Create a new model on my transmitter. I made the mistake of trying to re-use the existing model memory setup to fly my Tricopter where the Tx is programmed to do all the mixing and 120° CCPM. That job is taken over by the Arduino so a new model with just the basic config can be used.
2) Adjust (increase) the Throttle ATV such that the minimum throttle shown in the MultiWiiconf software is about 950. Once the Arduino sees a low enough throttle output, it will be able to arm the motors and set them at idle. If the Arduino reads anything above minimum throttle, the motors won't start as a safety feature.
3) Adjust the rudder / yaw control Dual Rate, ATV so that the output is in the 1000 to 2000 range in MultiWiiConf.
I'm still using the MultiWiiConf_prebis_1.6 only because I'd already configured it and had it up and running. Version 1.6 is the current version which I just need to configure and upload to the board. When the time comes, I'll try out the online configurator here http://ardupirates.net/config/MW_Config.php.
Now that everythings moving in the right direction in the software, it's time to put the props back on for a test flight. The old gyros will stay on till I'm sure everythings working ok.
Triwiicopter: Building the Brains
The next step to the tricopter project is to swap out the 4 HK401B gyros for an Arduino micro-controller hooked up to a Wii Motion Plus 3 axis gyro all mounted on a custom made PCB. The theory is a much more stable platform for getting some decent aerial video and photos.
The directions I'll be following can be found here;
http://www.rcgroups.com/forums/showthread.php?t=1261382
http://www.rcgroups.com/forums/showthread.php?t=1332876
http://www.rcgroups.com/forums/showthread.php?t=1340771
http://www.rcgroups.com/forums/showthread.php?t=1348268
The parts needed are;
2) Wii Motion plus (the innards of) 
4) An FTDI to plug in the USB and provide serial comms to a PC. 
5) Header pins.
The first step is too solder the Arduino and WMP onto the PCB. The hardest part is holding the header pins in place while flipping the board upside down to solder the bottom of the pins. Try using polystyrene foam or masking tape to hold the pins straight. I used double sided foam tape to hold the WMP in place and to provide some form of protection from vibration. I'll look at this again depending on what the output is like from the WMP sensor. Once the Arduino, WMP and header pins are all in place, it's time to upload the MultiWii 1.6 code to the Arduino. This link is quite handy as it appears to be the best place to go to check for updates as opposed to trawling the forums.
Here is where I struck the first hurdle. I kept getting error "avrdude: stk500_getsync(): not in sync: resp=0xf8, avrdude: stk500_disable(): protocol error, expect=0x14, resp=0xd1". After an hour or so of Googling and forum reading, I tried reversing the way the FTDI board was plugged into the Arduino and voila it worked. The proper direction is contrary to the images I had looked at on the net. The pin naming on the board didn't help much and is ambiguous probably due to the lack of space. After reversing the FTDI, the code uploaded first go with plenty of flashing "Rx / Tx" LEDs on the Arduino and FTDI board.
Once the Arduino is running the code, I start the MultiWiiConf software to check the output from the WMP sensor. This software allows configuration and fine tuning to be made to the parameters governing the stability and responsiveness of the Triwii. For now though I'm just using it to check that all three axes of the WMP are sending a signal. The USB connection powers the Arduino which in turn powers the WMP sensor so at this stage I should be getting output. After selecting the right COM port in the software and then "start", the graphical interface appears to be showing everything working ok. The GYRO_ROLL, PITC and YAW all change in value as I tilt the board. I believe the ACC_ROLL, PITCH and Z are active once the Wii Nun chuck is added in for auto stabilisation.
Next step, mount the board on the existing tri, unplug the gyros and plug the ESC inputs into the triwii board.
Tricopter 3 camera view
Just a quick link to the latest video with 3 camera angles. 1 from the tripod, 2 from my hat and 3 from onboard the tricopter.
Tricopter configuration for Futaba 10C
With a few flights under my belt now I'm starting to get a feel for what needs adjusting. Below are photos of my current config. They may not be the final and best but it's better than my initial settings where pitch and bank were way too sensitive and I dialled back the gyro gain / throttle curve.
Here are a few points garnered from rcgroups worth considering for optimising balance of the tri;
- I have weighed my tri at each boom and moved things things to suit.This balancing made a big difference.
- I found it really important to get the swash mix for the elevator and aileron right. As with a heli the higher the value for these two will make it more touchy. This will change from model to model but mine are set fairly low. There is definatley a "sweet spot" for the setting. I went too low and it became tough to fly.
- Also I powered my tri up ready to fly then increased my gyro limits one at a time with my throttle at zero until my motors just started to turn then backed them off until the motor stopped.
- And, of course, dialled in some expo on the elevator and aileron.
- Also some expo on the pitch helped with hover maintenance.
- Then it was suggested that I balance the props.
- The numbers in the SWASH MIX menu do nothing more than control HOW MUCH TOTAL MOVEMENT you will get for AILERON CYCLIC, ELEVATOR CYCLIC, and COLLECTIVE PITCH.
Tricopter troubleshooting
Feeback from rcgroups suggested the bullet connectors could be a likely source of motor dropouts I was experiencing. I decided to re-solder the 3mm bullet connectors on the troublesome ESC and give it a whirl. Unfortunately on powering up, the motor still stuttered and wouldn't turn. Time to swap the ESC.
My spare ESC was in use in my eHawk 1500 which also happened to have different connectors (1.5mm bullet and JST). It was quicker to pull the heatshrink off both ESCs (the suspect and replacement ESC) and remove the wires at the PCB end rather than re-solder 6 bullet connectors, 1 JST and 1 XT60 connector. With all the swapping of motors and ESCs I've been doing to troubleshoot, I have a number of cable ties still not trimmed short. I've been using the releasable cable ties which I found to be pretty good. Picked them up from Officeworks.
Another test flight and it looks like it was the ESC after all. I've put two 2200mAh batteries through it and not once did the motor stop. Well not until I crashed it and broke the yaw mount.... again. I must find a better way to mount that motor. Or stop crashing.
Once I get the hardware sorted out I can move onto fine tuning it, then the Arduino controller, then maybe one day, mount the GoPro.
KK Multicopter crash compilation video
My tricopter is far more fragile than this little beast.
kk multicopter - crashs from warthox on Vimeo.
Tricopter troubleshooting
If the motors are numbered 1, 2 & 3 in clockwise order starting with the rear yaw control motor as '1', then today I swapped motors 2 & 3 to troubleshoot the number 3 motor stopping dead intermittently. I found that the problem did not follow the motor after I swapped them.
The next suspect is then the #3 ESC and it's soldered connections.
Luckily my eHawk 1500 uses an identical Hobbyking 15-18A Super Simple (SS) ESC so I'll swap that for the tricopter suspect ESC. The downside is my eHawk uses JST connectors so I'll need to solder an XT60 on the battery side and some 3mm bullet connectors on the motor side.
Hopefully the result will be a stable setup so I can focus on learning to fly it and get the Arduino board setup.
Tricopter Flight test
I've got a couple of flights under the belt now but there's a persistent problem with the front right motor. It keeps stopping dead. This isn't so bad when its 30cm off the ground but when it's a few meters in the air there's potential for more damage. I caught one crash on the trusty little keychain camera, one mounted on my hat and the other mounted on-board the tri when the motor failed.
I checked all the connections, added padding to the gyros for vibration dampening and re-calibrated the throttle and tried again. Unfortunately the same result with that motor stopping mid-flight. I pulled out the trusty iPhone 4.0 and captured some video to help diagnose the problem over at rcgroups.
I've decided it's probably a dodgy motor or maybe the ESC. The motor is out of stock at HobbyKing so I ordered a virtually identical one from lowpricerc.com. At about six bucks each, I considered ordering three to make sure I have identical motors all round but when trying to order them, I got the "out of stock" error here as well! Turns out they had two left so I snapped up both. I'll replace the dodgy motor and keep one spare.
Just in case I grabbed a replacement ESC to help troubleshoot the problem. I went with the Turnigy Plush 18 Amp ESC because I already have the programming card and when I originally bought all the parts, this is the ESC I wanted to use but it was out of stock, surprise surprise.
So now I wait for my replacement motor until I try again. In the meantime I'll go learn some Arduino programming so I can get rid of the 4 HK401B gyros and use the Wii sensors instead. Apparently the Arduino controlled TriWiiCopter is more stable.
Tricopter build: Hooking it all up
Once all the soldering has been taken care of, it's pretty much a case of running all the wires making sure they can reach and connecting them all together. I followed the diagrams shown below. I don't take any credit for the diagrams. I found them by searching through the rcgroups.com forums and in particular this thread here.
Channel 1: Gyro #1 input.
Channel 2: Gyro #2 input.
Channel 3: Gyro #1, 2 & 3 sensitivity input connectors.
Channel 4: Yaw Gyro #4 input.
Channel 5: Yaw Gyro #4 sensitivity input connector.
Channel 6: Gyro #3 input.
Channel 7: BEC input.
Channel 8: LED light strip switch.
The photos below show the wiring before I tidied it up and also swapped the Futaba R617FS 7 channel 2.4Ghz receiver for an OrangeRx Futaba FASST Compatible 8Ch 2.4Ghz Receiver from HobbyKing. I needed the extra channel to make the LED strip switch on and off from the transmitter. Next I'll go through the programming I used for my Futaba 10C radio. This is my first "Heli" setup so I'd be surprised if I get it right first time.
Tricopter build: Wiring harness
I used 14 AWG wire to make the wiring harness connecting the ESCs to the main battery (3S 2200). This is the first project I've not used deans plugs in preference for the XT-60 connectors. Deans plugs were difficult to pull apart and expensive in comparison. To measure the length of wire and get the harness in approximately the right lengths, I started the build from the out tip of the arms and worked my way in. Start with mounting the motors, hook the up to the ESCs, then lay the main power harness wires out such that they all reach back to the probable location of the main flight battery. Once all the wires are cut to length, solder up each of the connectors.
