The first time I built a power distribution / wiring harness for a tri / quadcopter was back in December 2010 (http://fangin.com/blog/2010/12/07/tricopter-build-wiring-harness/) and I chose the most direct solution which was to solder all the cables together. I say "most direct solution" because in hindsight, it's not the simplest solution. The drawbacks of this solution include;
- It's more difficult to layout all the wires and get the lengths planned up front.
- Twisting the wire together and soldering 4 or 5 wires at one junction gets messy.
- I tried to link all the wires at one point (http://fangin.com/blog/wp-content/uploads/2010/12/1000000286-Large.jpg) to go into the battery which made it difficult to get the wire into the XT60 connector.
A neater, simpler and all round better solution is a power distribution board where a central, double sided PCB board (copper on both sides) is located centrally in relation to the ESCs / motors and all the wires connect back to this PCB.
What you'll need.
- PCB - Double sided.
- Red / Black Wire
- Solder / Soldering iron
- 20mm heatshrink tube.
- Cut a small board approximately 35 x 15 mm of the double sided PCB.
- Prepare the wires and board by soldering the ends of each wire and the board where the wires will go. You may want to consider orienting the wire to suit the layout of your multirotor. For example an X-Quad you may want to have four wires coming off the board in an X layout.
- Solder the wires to the board. Turn the board over and repeat for the other polarity wires.
- At this point you're almost ready to seal the board up with some heatshrink tube. Before you do! Use a continuity test on a multimeter to ensure 1) All the ground wires are connected and 2) There is no connection between the positive and ground planes.
- If you're worried about wires moving or foreign objects getting into the heatshrink, smother both sides of the board with glue from a hot glue gun. That will help keep the wires in the right place and prevent a short circuit between the two polarities should something conductive work it's way into the housing.
- Now you can solder your favourite connectors at the end of each pair of wires. In the photo shown below I've used XT60 connectors on a harness made for a tricopter.
Today was the first flight outside the confines of the garage. It was quite windy at the local oval making it fairly difficult to maintain stable flight. It's not meant to fly nicely, it's meant to look weird and fly weird and that's exactly what it does.
To answer a few questions about the specs of the Quad-Y-Copter (V-Tail) here are some details on the config;
Motors: All four are rctimer.com 750kV
ESCs: Turnigy 30Amp. I haven't measured the current draw but I'm sure 30A is overkill. http://www.hobbyking.com/hobbyking/store/uh_viewitem.asp?idproduct=2164&aff=257015
Props: 3 Bladed 9 x 5 regular and counter rotating.
MultiWii Software 1.9 http://code.google.com/p/multiwii/downloads/list
Y4 Config as per http://www.multiwiicopter.com/pages/multiwiicopter-wiki
The frame is 12mm x 12mm Tassie Oak arms and 3mm ply.
Inverted V-Tail arms at 20 degrees.
motor = PIDMIX(+0,+1, -1/2); //REAR_R
motor = PIDMIX(-1, -1, +1/5); //FRONT_R
motor = PIDMIX(+0,+1, +1/2); //REAR_L
motor = PIDMIX(+1, -1, -1/5); //FRONT_L
If you do nothing else, skip to 48 seconds in the video below and watch the crash when I hit a tree and land right side up. I ask you how many types of models / electric helis can you punish with that poor piloting and keep on flying? If that had of been an electric heli, I would probably have been up for new blades, boom and miscellaneous other bent rods along with the time to take apart and re-assemble. The QuadYCopter is made from ply, 12mm x 12mm Tassie Oak booms, cable ties, 3mm aluminium and 3mm bolts (both nylon and steel). The two front arms are held in place with cable ties which means in the event of a crash, there is a fair bit of give without breaking anything.
The photos show the main booms are quite a lot longer than needed. That's the result of experimenting with the position of the motors and moving them closer into the centre. The unexpected benefit of this is protection for the propellers. I haven't broken one prop yet with this config.
The Y configuration of the booms is definitely easier for me to fly and keep orientation when compared to the symmetrical Quad. The bright red anodised aluminium landing gear at the rear is also a great help. In the video at about 4 minutes I do some "high-ish" altitude video and maintain good visibility, smooth flight and it descends quite well. Some configs I've flown haven't coped well when descending rapidly and wallow quite alot that sometimes ended up in uncontrolled oscillations that didn't end pretty. Not so with the QuadYCopter. I could descend quite rapidly and even up up the throttle quite aggressive when it got low and it would recover quite well maintaining a flat attitude.
The V-Tail config has good authority with plenty of yaw control. To be honest, in all my RC flying (mostly planes) I've never used the rudder (equivalent) until I started flying multirotor. The QuadYCopter can do some quite tight turns and makes a great prop noise when pushed hard. With a lighter touch, it will do graceful arcs producing some nice stable video footage.
Stability is good in "aerobatic" mode but in "stable" mode I'm still getting oscillation. I reckon some PID tuning should sort that out.
So for some ratings out of 10;
Things to do;
1. Sort out the "Stable" mode.
2. Install FPV gear
3. Maybe install some LED strips.
There's a few things I'm trying out to get the QuadYCopter as stable as the QuadCopter is;
- Three Blade props
- 4S Battery
- Shorten the front arms
- Restore the PID values to default
- Custom code.
By far, the biggest change / improvement has come from using Three bladed props and a 4S battery. Some might argue a well balanced two bladed prop is just as good as a three bladed but in my experience, the 3 blades seem much easier to balance. The 4S battery also makes a huge difference to the throttle response. It's much zippier and for example when I jockey the throttle on 4S, the Quad actually jumps and dips. When I do the same on a 3S battery, the response just isn't there and it's sluggish.
I'm trying modified code specifically for Y4 V-Tail I found in the forums here http://www.multiwii.com/forum/viewtopic.php?f=8&t=665
The default code is;
motor = PIDMIX(+0,+1,-1); //REAR_1 CW
motor = PIDMIX(-1,-1, 0); //FRONT_R CCW
motor = PIDMIX(+0,+1,+1); //REAR_2 CCW
motor = PIDMIX(+1,-1, 0); //FRONT_L CW
The modified code is;
motor = PIDMIX(+0,+1,-1); //REAR_1 CW
motor = PIDMIX(-1,0, 0); //FRONT_R CCW
motor = PIDMIX(+0,+1,+1); //REAR_2 CCW
motor = PIDMIX(+1,0, 0); //FRONT_L CW
Today I moved the two forward motors back on the arms so they're equal distance from the centre as the two rear motors. Initially I had them further forward to counteract the weight imbalance of having two 'sweptback' arms but with proper battery placement and I want to use a GoPro up front, I don't think I need more weight up front.
I restored the PID values to default but still get some osciallation in "stable" mode. before I lower P any more, I need to see what the effect of moving the motors has.
There's a few different names that might be applicable like a Y4, Inverted V-Tail, Y-Copter but I think I'll call it the QuadYcopter and it flies! All I had to do before this video was reverse the direction of two motors and it flew better than expected considering the lengths and angles are all eyeball precision.
I expect the QuadYcopter should deliver the best aspects of Quads and Tris;
- No mechanical tilt needed on the rear motor (tri negative)
- Larger unobstructed field of view looking forward (tri positive)
- Non symmetrical airframe which should be easier for orientation at long distance (Quad negative)
Notice in the video, it's quite twitchy in pitch. I reckon that's related to the CoG which I've moved forward by mounting the battery all the way forward. This isn't a big problem as I'll probably mount a GoPro up front which will further help with balance. The underside mounting for the battery means it can be moved all the way from the rear to the front to compensate for camera / cameraless flight.
I still need to mount a low voltage buzzer on the airframe. The problem is, I've started using an 1800mAh 4S battery whereas most of my other batteries are 3S. I've had to order a couple of voltage 2S-8S detectors that let the voltage be set via a jumper so I can fly with either 3S or 4S