Turnigy Model Be Found
Going by the name of the Turnigy "Be Found" device, I get the impression it supposed to help you find your model if in the event of a mishap, it goes down somewhere hard to find. I've got a number of issues with this which I'll outline below. But then take a look at the website description (http://www.hobbyking.com/hobbyking/store/uh_viewItem.asp?idProduct=20578) and it describes it more as a pre-flight safety check device to audibly warn you if either your battery voltage is low or you lose the radio link during the pre-flight check you do before every flight (right - every flight).
From the website:
"This Handy unit will emit a loud beep if your receiver loses radio signal or when the voltage of your models radio system drops below 4v. Perfect for testing ground range of receivers and ensuring that your radio system has not dropped to an unsafe voltage before each flight."
Let's assume the low voltage part of it works (I'll have to assume because I didn't bother testing it), let's take a look at the worse case scenario where the model is lost in-flight and has to be retrieved in thick bush. Here are the drawbacks and why I reckon it won't work;
- It didn't beep when I switched my Tx off. That's a pretty drawback as number one. Am I doing something wrong? Check the youTube video for how I tested.
- Of all the models I've seen crash, the battery pack is quite often not connected to the receiver anymore (ie no power to the buzzer).
- I reckon it introduces another likely point of failure. The in-line connector for the servo was a bit dicky and bent and the plastic cover stopped me from plugging it in properly the first time.
- If I have to rely on the low voltage buzzer to go off while I'm searching for a lost model, I could be waiting a while for the pack to drop below 4V.
- Even as a pre-flight check device, if I'm standing 10-15 meters away from my model at a busy club field, and it did start beeping, I'm not convinced I'd hear it.
Overall, as a safety device, I don't think it adds much value and your radio setup is probably better off without another point of failure being introduced (even if it is only on one channel). This one is a Pass.
Using the HobbyKing servo tester to setup servo arms
Installing servos and getting the arms in the right position can be a pain if you haven't got around to setting up and connecting your transmitter yet. A servo tester like this one http://bit.ly/xUeoyB means you can find the centrepoint and test the throws all without the Tx. In the photos and videos below I've got three Hextronik HX5010 servos installed and pretty much centred without using any radio gear.
Quad-Y-Copter (V-Tail) Specs
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
http://www.rctimer.com/index.php?gOo=goods_details.dwt&goodsid=123&productname=
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.
http://www.hobbyking.com/hobbyking/store/uh_viewitem.asp?idproduct=5250&aff=257015
http://www.hobbyking.com/hobbyking/store/uh_viewitem.asp?idproduct=5248&aff=257015
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.
Custom mixing.
#ifdef Y4
motor[0] = PIDMIX(+0,+1, -1/2); //REAR_R
motor[1] = PIDMIX(-1, -1, +1/5); //FRONT_R
motor[2] = PIDMIX(+0,+1, +1/2); //REAR_L
motor[3] = PIDMIX(+1, -1, -1/5); //FRONT_L
#endif
QuadYCopter video and performance review
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;
Durability: 9
Stability: 7.5
Aerobatic: 8
Visibility: 8
Simplicity: 9
Things to do;
1. Sort out the "Stable" mode.
2. Install FPV gear
3. Maybe install some LED strips.
QuadCopter by the Moonlight
This photograph wastaken by Nick Sage at our Christmas club meeting at the LDMFA field. It shows my MWC Quad hovering with the moon partially covered by cloud in the back ground.
Optimising the QuadYCopter
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;
#ifdef Y4
motor[0] = PIDMIX(+0,+1,-1); //REAR_1 CW
motor[1] = PIDMIX(-1,-1, 0); //FRONT_R CCW
motor[2] = PIDMIX(+0,+1,+1); //REAR_2 CCW
motor[3] = PIDMIX(+1,-1, 0); //FRONT_L CW
#endif
The modified code is;
#ifdef Y4
motor[0] = PIDMIX(+0,+1,-1); //REAR_1 CW
motor[1] = PIDMIX(-1,0, 0); //FRONT_R CCW
motor[2] = PIDMIX(+0,+1,+1); //REAR_2 CCW
motor[3] = PIDMIX(+1,0, 0); //FRONT_L CW
#endif
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.
QuadYcopter Maiden Flight video
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
Timelapse GoPro extended by external power source
Ran the GoPro from about 2pm till 8pm on the upstairs balcony. I'm not sure how long the GoPro battery would last so I hooked it up to a LiPO 2650mAh battery via a uBEC. I checked the charge before and after and it had used about 40% or about 1060mA. I think the GoPro battery is 1100mA so it would have been pretty close to dead flat.
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.
