Multirotor loops and rolls just got easier with OpenPilot
With the latest release of the OpenPilot software version 14.01 come two new features (among others) that when combined, make flipping and rolling a multirotor (MR) even easier. A new flight mode called "Rattitude" is a hybrid of the self levelling "Attitude" and the more aerobatic 'Rate' mode. In "Rattitude" mode as the control stick on the transmitter moves out from the centre, the flight mode of the craft changes from 100% Attitude through to 100% Rate with varying degree of mixture in between. The effect means that letting go of the sticks means the MR will return to self levelling (ie Attitude mode) but you can still throw it around as the control sticks move out from centre, you get the aerobatic response of Rate mode.
Normally you would have to flick a switch to go from Attitude to Rate. In Attitude mode, because it's always trying to self level, to maintain forward flight you have to constantly be holding the stick forward. It feels like you're fighting it to a degree for the whole flight. Also Attitude mode limits the maximum angle of pitch and roll so if you try to roll in Attitude mode, you'll roll to the angle defined as the maximum and not go any further around.
In Rate mode, it goes where you point it. If you roll to 45 degrees, the MR will attempt to hold that angle until you tell it otherwise. Rate mode can be intimidating for the novice pilot as the safety net of self levelling is removed and depending on the settings, Rate mode can fill quite 'slippery' if you're not used to it.
The other new feature in 14.01 is Cruise Control which from my limited reading of the topic attempts to maintain a steady altitude when the MR is turning or banking by slightly increasing the rpm to counter the slight decrease in lift). With Cruise Control comes a 'Max Angle' parameter that when set to 90 degrees, combined with Rattitude mode, means that as the MR rolls past 90 degrees, it automatically spins down the motors. That means the part of the roll when the MR is passing through the inverted (ie the props would normally be pulling it to the ground), the motors are automatically shut down which seems to make for a much tighter roll.
From personal experience I went from rolling and flipping with at least 10m height to doing the same at maybe head height. The first time I tried this combination it was quite weird to hear the motors shut down as it passed through the 90 degree vertical point but they came back up a few milliseconds later. Posts in the OpenPilot forum suggest that setting the Cruise Control Max Angle (CCMA) to 80 degrees and the degrees / second to 360 make for some nice smooth rolls.
The screenshots below show captures from the OPenPilot GCS software version 14.01 and the settings required to change to get this to work. I first tried it on my "beater" quad with a CC3D flight controller and liked it so much I put it on my "nice" quad with a Revo FC and Ov3rquad frame. The video below shows the results from these settings on both my CC3D and Revo controlled quads with CCMA set to 90 degrees and the Rate mode "Degrees / second" setting up at around 450-500.
The next thing I want to try is lowering the CCMA to 80 and deg/sec to 360 for the nice, "natural" roll and then go the other way to CCMA = 100 and deg/sec =720. Maybe with these settings I might get in a few double or triple rolls before hitting the ground.
Cutting the shaft on the NTM Prop Drive 28-26 1350KV / 310W
For the PVC 'BattleQuad' I'm building I ordered four 'NTM Prop Drive 28-26 1350KV / 310W' motors as I've used them before on a Hex 550 build and am quite happy with them. These motors are a little different in that you have to buy a seperate accessories pack to get a mount for the base of the motor and a prop adaptor. The motor is a little odd in the way that the shaft extends out the bottom of the motor and the prop adaptor is attached via three bolts on the opposite side from where the shaft protrudes from. In my previous build this wasn't a big problem because the way the motors were mounted, the shaft could extend below the arm without interfering.
On my current build, the PVC 'Battlequad', the way the motor slides onto the arms, the shaft was going to get in the way. I could easy shorten the arms and cut a line down the length of the PVC pipe but I've got some plans for extended length arms so I want to keep them intact. I decide to cut the shaft off the motors. The concern with this option is in the process of cutting with the Dremel, the fine metal dust created from the cut could potentially end up getting inside the motor.
The first method I employed to avoid this problem was to put the motor back into the re-sealable plastic bag it came in, poke just the shaft through the plastic so the motor is contained inside the back and just the shaft sticks out. The problem with this is that the bag wasn't up to the job of withstanding the red hot metal filings and a hole was quickly burnt in the bag and became a collection point for all the metal filings. My solution the keep the filings out of the motor had had the opposite effect and was actually diverting filings into the confined space around the motor and it's precious little magnets.
My next solution worked much better and was even simpler. Take a piece of cloth tape (about 8cm wide by 15cm in length), fold it in half and cut a small triangle in the centre of the fold. Flatten out the tape so now you have a piece of tape with a small diamond shaped hole in the middle, just large enough for a motor shaft to fit through. Put the tape over the motor with the shaft protruding through the small hole and Dremel away. If you've cut enough length of cloth tape, there should be plenty left to wrap around the motor and keep the metal filings out. The cloth tape is much sturdier and kept the red hot metal filings out without melting.
Quadcopter Parts List
I was asked recently what would be a good way to start in multirotors. The first question was "A tri-copter must be simpler and easier because there's only 3 motors?". I disagree. I've built quite a few tricopters and on each one explored a different way of building the yaw control mechanism on the tail motor. Some worked well, some not so well but by the time the servo is mounted and linkages hooked up, it all gets more complicated and less reliable compared bunging on a fourth motor and prop spinning in the opposite direction. I think what finally converted me was assembling the DJI F450 frame with the Naza controller. This quad was smooth and stable from the first flight and is an ideal platform for mounting a GoPro camera on for some aerial photos & videos. The downside of the DJI is that it's not cheap. I spent over $600 on the Flight controller, frame kit and GPS module and that's assuming you already have LiPo batteries, LiPo charger, radio control transmitter & receiver and other bits and pieces. It can quickly become an expensive option especially if you're just getting started.
Another option is the "toy quads" you'll find in electronics stores or maybe even the local shopping centre. They're cheap and maybe a good way to get a taste for flying multi-rotor but they have certain disadvantages;
1) The parts are generally not re-usable for your next project. The motors, ESCs and controller are so deeply integrated they're not easily adapted to another frame.
2) Often they're quite small with payload capacity to match. The small quads will struggle to carry much more than a lightweight spycam let alone a GoPro or pocket digital camera.
So what to buy for a simple, cheap, respectable quadcopter with parts that could be re-used in your next project, maybe a hexcopter. This shopping list should cover absolutely everything you'd need to start from scratch.
Flight Controller: $29.99 Hobbyking KK2.0 Multi-rotor LCD Flight Control Board
Auto-level with and LCD screen for configuring and tuning. Eight outputs good for tri-copter up to Octo-copter. The downside is no barometric pressure sensor (height hold) or GPS (position hold) but at that price, those features aren't expected. It also has a built in voltage monitor that outputs an audible alarm at a programmable low voltage level. This feature requires a couple of extra wires soldered to the board and is well worth the trouble.
Frame: $17.99, Q450 Glass Fiber Quadcopter Frame 450mm - Integrated PCB Version
A simple, sturdy frame that comes with an allen key for the 2.5 and 3mm boltsand even a velcro strap for the battery. The lower board has an integrated PCB which means there's no need a messy power distribution cable arrangement.
Motors: $14.99 (x4), NTM Prop Drive Series 28-26A 1200kv / 250w
Ideal size and power for this frame. The mouting holes align perfectly. Something odd with this motor I hadn't come across before was the shaft sticking out the rear / bottom of the motor. The accessories pack is needed as a propeller mount and uses three bolts to attach to the motor. I quite like this method as compared to the prop savers with the rubber o-ring or the collet style adaptors.
$1.89 (x4), NTM Prop Drive 28 Series Accessory Pack
You won't need the motor mount or the four silver screws, just the prop adaptor. With the Q450 frame, the bolts go through the frame and straight into the bottom of the motor.
$12.19 (x4), TURNIGY Plush 30amp Speed Controller
Simple, reliable, does what it's supposed to without any fuss. The difference in weight between the 18, 25 and 30 Amp ESCs is barely worth compromising the current capacity for.
$1.59, PolyMax 3.5mm Gold Connectors 10 PAIRS (20PC)
Some might solder their motor wires straight to the ESC but I've never been organised enough to plan that far ahead. I need the flexibility to swap any two of the three motor wires. I've read alot about bad or loose connections that have caused crashes. I've never experienced this type of failure. I think probably because it all comes down to a good solder joint.
$2.46, Slow Fly Electric Prop 8045R (4 pc - Green, RH Rotation)
Eight inch, Right Hand (RH / Clockwise) rotation. Four to a pack but you'll only need two with two spares. At these prices though, if you're ordering any spares, props should be high on the list. Get two packs.
$2.29, Slow Fly Electric Prop 8045 SF (4 pc - Green)
As above but they turn the other way. I like coloured props (as opposed to black) because they're much easier to see. In bright daylight, black props look almost invisible compared to green props which seem to present a good contrast against the sky.
$4.75, 10CM Male to Male Servo Lead (JR) 26AWG (10pcs/set)
These connect the receiver to the inputs on the flight controller board.
$16.38, Turnigy 2200mAh 4S1P 20C Lipo Pack
Minimum capacity and C rating you'd want to use for a decent flight time.
Now up until this point, it's assumed you already have some RC equipment from other projects. For those that are starting out and need a LiPo charger and Transmitter / Receiver etc, here are some suggestions.
$53.95, Turnigy 9X 9Ch Transmitter w/ Module & 8ch Receiver (Mode 1) (v2 Firmware)
From accounts I've read online, the Turnigy radios are a good way to get started. A nine channel radio and receiver for just over $50 is good value! This package doesn't come with batteries or charger but seeing as most people will already have these, it makes sense for Hobbyking to exclude these parts.
$6.89, HobbyKing 1500mAH LiFe 3S 9.9v Transmitter pack.
A Tx is no good without power. Compatible with the charger below but you'll need another lead for charging.
$16.99, HobbyKing 50watt 5A X-Charger/Balancer
This battery charger will be enough to get you up and running doing balanced charges on LiPo's. It will also charge NiMH and NiCd batteries often used in transmitters. Note - it is a DC only input so you'll have to hook it up to a car battery or similar and can't plug it onto 110 / 240 AC wall outlets. For a charger with both DC & AC input, look at a "B6-AC Plus - Charger/Discharger 1-6 Cells Dual Power (COPY)" or better.
$2.69, Charging harness
Use this harness to charge the Tx LiFe battery. You'll probably never use ALL the connectors on this charging harness but even if it means cutting some off and re-purposing with a different connector, for a few dollars it takes the pain out of soldering up wires to banana leads.
I think that's pretty much everything you'd need to get in the air with a decent quad. The best thing about this setup is that down the track you could directly swap the KK2.0 control board for maybe a DJI Naza controller and add altitude and position hold, without having to change any motors or ESCs. The parts are all fairly cheap to replace so those first few crashes shouldn't be too painful on the wallet. If you can afford to, get two frames (1 for spare) so you don't have to wait weeks for another delivery from Hong Kong to repair / replace parts. Spare propellers are a must have and considering the price of them, it's a no brainer to order a few more packs of them.
There are a few more items like spare battery packs and LED strip lighting that you'll probably want to add down the track but for now the objective is to get a quad in the air for cheap, but not too cheap to make it nasty.
Ok so to recap, here's the parts list summary and totals;
Flight Controller: $29.99 Hobbyking KK2.0 Multi-rotor LCD Flight Control Board
Frame: $17.99, Q450 Glass Fiber Quadcopter Frame 450mm - Integrated PCB Version
Motors: $14.99 (x4), NTM Prop Drive Series 28-26A 1200kv / 250w
$1.89 (x4), NTM Prop Drive 28 Series Accessory Pack
$12.19 (x4), TURNIGY Plush 30amp Speed Controller
$1.59, PolyMax 3.5mm Gold Connectors 10 PAIRS (20PC)
$2.46, Slow Fly Electric Prop 8045R (4 pc - Green, RH Rotation)
$2.29, Slow Fly Electric Prop 8045 SF (4 pc - Green)
$4.75, 10CM Male to Male Servo Lead (JR) 26AWG (10pcs/set)
$16.38, Turnigy 2200mAh 4S1P 20C Lipo Pack
$53.95, Turnigy 9X 9Ch Transmitter w/ Module & 8ch Receiver (Mode 1) (v2 Firmware)
$6.89, HobbyKing 1500mAH LiFe 3S 9.9v Transmitter pack.
$16.99, HobbyKing 50watt 5A X-Charger/Balancer
$2.69, Charging harness
A grand total of $272.25. A bit pricier than I was aiming to get it but don't forget that theres about $80 worth of radio and charging gear that can be re-used in the next multirotor. Once you've built one, you won't stop at that. Tri, quad, hex, octo ... they're all possible with these same parts.
****If I've forgotten anything on the list, leave me a comment below 🙂
Flips & Rolls with the Naza F450 Quad
This video shows my first loops and rolls with the DJI Naza F450 Quad. I did at least one in every direction (left, right, forwards and backwards). The entire flight was flown via FPV which I found much easier for these moves. Flying line of sight at this height and distance makes it hard to maintain orientation.
A guy that started flying the F450 about the same time as me told me how he tried to roll it, it got half way and dived into the ground. Broke an arm or two and some props. Thanks to the well thought out F450 frame, he was back up and running in no time but after hearing such a tale I was a bit apprehensive to try it myself..... until now. With my FPV gear up and running it's much easier to gain a lot of height and maintain orientation.
The setup is a stock F450 quad with 8" props and 4S battery (4000mAh on this flight). Other than the gain settings as described here (http://fangin.com/blog/2012/08/07/dji-naza-f450-gain-settings-flips-and-rolls/), there's not much to it. Gain plenty of height and bang the stick over. I can see how if the gains were set too low, the roll rate might not be quick enough to complete the roll without losing too much height.
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4S 5000mAh on the Naza Quad
I threw the 4S 5000mAh battery on the DJI Naza F450 Flamewheel quad. I expected the battery might be a bit too heavy weighing in at 530gr plus the weight of the GoPro camera plus EagleTree Logger, EagleTree GPS and the DJI GPS, the Flamewheel has put on a bit of weight since it's maiden flight. I'll have to weigh all those parts and see what they contribute to the all up weight.
I was pleasantly surprised at the climb rate even with a half kilo battery onboard. The EagleTree log shows I flew for around 16 minutes of fairly sedate hovering with six ascents to high altitude.
DJI Naza Voltage Protection Levels
This is how I've set my first and second level protection voltage thresholds. I found the default setting with 14.8 Volts in the 'No Load' without any value in the 'Loss' field meant the Second Level Protection kicked in far too early and the Quad became sluggish to ascend. Even at full throttle, it would only rise very slowly. Flicking it into manual mode and the Quad would take off like a rocket. That tells me the battery has plenty of juice left in it but the Naza is artificially limiting the maximum throttle available by slowly moving the mid-point up.
The results from the Eagle Tree logger show a loaded voltage level throughout the entire flight. 14.4 and 14.2 is probably a bit conservative but I'll test it out and see how it goes. I reckon I might change it to 14.2 and 14.0. We'll see.
****Update - 5th July 2012
I think these values are too conservative. On the last flight, 2nd level kicked in and I still had about 50% left in the 2650mAh 4S. I've set them to 14.2 and 14.0 (zero loss) and will do another test flight. The Eagletree logger is fantastic for this type of problem.
Stabilise Filter Example – Telstra Tower
On the left is the original footage from the DJI Naza F450 GoPro. On the right is the "stabilised" version. By uploading the original to YouTube, applying the stabilise, then downloading the MP4 and running it back through YouTube you're able to see a side by side comparison.
The stabilised filter has some funny side effects where it appears as though the video is suddenly zoomed in and out. The blurriness of the RHS probably isn't a fair representation because that side has been uploaded, compressed, and downloaded.
The process does crop the video slightly and uses the edges as a buffer to remove the sudden movements from side to side or up and down.
The videos are in pretty good time sync but you may notice the RHS looks like it's behind the LHS. This lag is due to the smoothing effect of the filter and sudden movements take a little bit more time to catch-up with the RHS.
I've since changed the mount that the GoPro uses and without any post-processing the video is quite smooth. It will be interesting to see how smooth a video would look from the new mount after applying the stabilise filter.
Overall for this type of video, the stabilise filter does a pretty good job.
DJI Naza GPS X,Y,Z co-ordinates
The shots below show my settings in the DJI Naza Assistant software for the X, Y & Z co-ordinates and what that translates to on the Quad. The first time I flew with the GPS, I didn't bother to set any parameters and GPS mode wasn't very good. As soon as I activated it, the quad would bank left and drift quickly until I re-engaged attitude mode.
I made three changes before the next flight. 1. Mount the GPS on the stick provided, 2. Point the arrow on the GPS towards the front and 3. Enter the co-ordinates in the software configuration. After another test flight, the GPS holds position pretty well. What I don't know is what had the most effect (the mount, direction or co-ordinates). I'm hoping it's the co-ordinates in the software because I'd prefer not to use the stick mount because it makes it bulkier to pack and more prone to damage on a hard landing. I think I'll try going back to double sided foam tape and mount it directly to an arm.
The pictures below show these settings X = -4cm, Y=4cm and Z=-9cm and what they look like in the real world.
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EagleTree Logger V4 on the DJI Naza F450
The first full flight with the EagleTree Logger v4 running on the DJI Naza F450 with GPS. The first 140 seconds show little activity while I plug things in and wait for GPS lock. When I eventually takeoff with a 4S 2200 Nano-tech LiPo, the voltage drops to 15.4 Volts and within 40 seconds drops down to 14.8 Volts as you'd expect from a 4S battery. It seems to hold the voltage fairly well throughout the flight keeping in mind it was fairly sedate backyard hovering with the GoPro onboard and recording. The voltage seems to start decling quickly after about 500 seconds where there's a few spikes in current and corresponding drops in voltage where I did a few short sharp rapid ascents with the throttle wide open. At about 670 seconds, the voltage drops too far and the second level protection kicks in where the Naza automatically descends. For my liking, it descends too rapidly but I'm not sure if that might be the result of setting the second level voltage protection level too low so there's nothing left in the pack to land safely. I wonder if I up the Voltage level, will the descent be more controlled when the Naza takes over.
I got about 2,000 mA out of the 2,200 pack which seems fairly good. The quad is loaded up with a GoPro, Naza GPS, Eagletree logger and Eagletree GPS so it's carrying a little more weight than usual. 8.5 minutes hover time seems pretty good I reckon. Average current draw with the 8" props is around 13 amps with a peak at 24.5. The 30Amp ESCs should be more than comfortable to handle that load.
This was the second flight with the DJI Naza GPS and all went well. There's been many rumours floating around the forums that the GPS doesn't work so well in the Southern Hemisphere (SH) and after my first flight I was worried they were right. During that flight, whenver I activated GPS mode the Quad would veer off to the left and never recover. After entering the X,Y,Z co-ordinates in the software configuration and mounting the GPS on the stick, it works great. At most the drift was maybe 1 meter but most of the time it seemed to hold position withing bout 30-50cm.
Next mission - Test the Return to Home (RTH) feature. I'll need a bit more space than the backyard though because it's supposed to ascend 20 meters, return to base, then land. Need to make sure there's no trees in the way. At the moment, the only way I have to trigger failsafe mode is to switch off my transmitter. That could be a bit nerve racking. In all my years of RC flying, I've never deliberately (or accidentally) switched off my Tx in mid-flight. I might have to make sure to have the video camera recording that one.
How to mount a GoPro to a DJI Naza F450
I'm not saying it's the best way, it's just how I do it and it seems to work well. Velcro on the bottom of the GoPro, velcro on the part of the F450 frame that sticks out the front then wrap a length of velcro around the entire camera. The "shutter" button can still be easily operated through the velcro.
Simple, light and works. I used to use the protective case but what's the worst that could happen. If I write it off, I'd have to replace it with a new version 2 GoPro. Damn. 🙂
