Starting out with MultiWii

Last night I unpacked my new MultiWii controller and plugged it into my PC.  I bought it from Hobby King and it comes ready to fly out of the box – configured for an X-quad, which is perfect for my carbon H-copter.

The Multi-Wii board attracted me because it comes with so many sensors out of the box.  Barometric pressure, compass, gyros and accelerometers as well as the option to add GPS in future.  That’s compared to just gyros on the KK board.  I love the KK board to bits – it’s a great board for line-of sight flying, allowing a fair amount of acrobatics and some nimble and fast flight.  It’s scary flying FPV with the KK though.  I managed a good FPV flight at the weekend (see video later) but it would be great to push more of the stability control onto the ‘copter for less stressful remote piloting.

I didn’t get the board hooked up to the quad or the receiver last night, just plugged it into the PC and fired up the Java tool.

I have to say I was very impressed with the board and the UI tool.  The tool shows a live trace from all of the on-board sensors and a 3D model of the ‘copter which moves in real-time.  Every single setting is configurable, including the PID terms, throttle travel, behaviour of the auxiliary “switch” channels and so on.

Hardware wise, the barometric pressure sensor was the star – it responds to changes in height of about 10cm, which is spookily accurate!  The only worry I have is the effect of wind on this sensor – I am wondering whether a wind shield is going to be needed for breezy days.

Down sides so far:  The GUI is a bit painful to use.  About 25% of mouse clicks are ignored or lost (I think because the refresh loop for the graph is running and the app is polling for user input).  Also, the numeric values are editted using very very very small sliders.  It would be much simpler to just enter the text!  Maybe these things annoy me more because I do that sort of thing for a living…

Expect more soon!  In the mean time, here’s an FPV video from this weekend…

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Repairs and FPV Setup

While repairing the crash damage to the Carbon-Copter I decided to do a more scientific investigation into the differences between carbon and aluminium…

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10mm x 10mm Carbon square tube weighs about 0.5g/cm while aluminium bar of the same dimensions (purchased from B&Q) is just slightly under 1g/cm.  That makes the maths easy – 150cm of bar needed for the carbon quad means a 75g difference between carbon and aluminium – which isn’t that bad.

Aluminium is cheaper and seems to be more crash-resistant too, plus I can pop over the road at lunchtime to buy some as opposed to ordering it from China.  So, I made up a complete set of parts using each material.

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With the ‘copter repaired I concentrated on setting up the FPV gear.  Sadly, I broke my little FPV camera – I think I caught a screwdriver on some of the components and shorted something.  It was only a tenner but I am still quite cross with myself for not taking enough care.

Anyway, I have the GoPro which can also output video for FPV use.  There’s a slight lag (less than half a second probably) in the video feed which makes it a bit weird and since I’m not willing to drill the waterproof case the camera has to fly “naked” which is a little riskier.  On the plus side, many people report success with exactly the setup pictured below:

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The garden isn’t the ideal place for testing with fences and walls in every direction, but my darling wife was kind enough to snaps some pics of the video feed on the garage telly while I had a nose over the neighbour’s fence flying line-of-sight.

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The feed was a little noisy but a lot of that is going to be due to the fact that the signal had to get through the garage roof.  Penetration is not good on 5.8GHz signals.  Need to sort out something a bit more portable and pop over to Dr J’s house for more testing this week.  Watch this space!

Christening, Cruising then Crashing the Carbon-Copter

I watched the BBC weather report with a growing sense of foreboding this morning.  A huge band of rain sweeping inexorably towards Newbury from the south coast, set to smother the whole of Berkshire under a blanket of liquid misery until Saturday lunchtime.  Nothing unusual, but particularly inopportune as I had a completed carbon copter and a suitcase full of batteries in the back seat of the car.

Luckily, the rain held off and Dr Johnson and I met up on the green to fly some multi-rotors in the blustery wind.  The Carbon-Copter performed stunningly…

Make sure you stick with the video (or hit fast-forward) as there’s some cool shots of the FireGoat from the air towards the end.

A tiny bit of transmitter tinkering was required: un-reversing the rudder direction, lowering the expo on the pitch and roll axes and so on.  After that it was just a case of whacking the throttle up and grinning like a fool as the quad danced around the skies.

In the end I got too cocky – of course.  Started with some backwards and forwards stuff, then progressed to attempting some lazy 8’s at increasing speeds.  Eventually I lost it and hit the ground.  Initially I thought everything was OK with the frame but on closer inspection I found that both legs and one of the front-back braces was cracked.

Amazingly though, it still flew.  There was a noticeable twist in the frame as I lifted off, but it continued to fly brilliantly.  Of course, now that the legs were broken and my money effectively spent I had nothing to lose – the lazy eights became less and less lazy until they became simply “eights” then “vigorous eights” and finally “broken quad eights”.

Hit the floor pretty hard and the carbon rods shattered into a thousand useless shards.  Time to go home and make some more!  The carbon sheet remains intact, so the repair will just involve cutting and drilling some new legs and braces.  £5 total cost, which isn’t a million miles from the cost of fixing the aluminium copter after similar crashes.

So I had fun and I perhaps went a bit too far with the aerobatics.  The carbon quad is an unmitigated success and I have a big smile on my face.  It’s also worth remembering that I built the carbon quad for slow moving videography and FPV, so maybe “mental eights” won’t be happening again too soon!

Carbon Copter Cables

Spent a couple of hours in the garage soldering the ESCs onto the new Carbon Copter tonight. Four was more than enough. The soldering is without a doubt the most annoying part of multi-rotor construction and I haven’t got a clue how people who make Y6 and Octos don’t go stark raving bonkers.

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The workbench was very busy with wires, all snipped from my last hastily built monstrosity. Shortened the ESC-to-motor cables from 300mm+ to about 100mm. That’s bound to save a bit of weight.

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Speaking of weight, the whole thing now weighs in at 1.2kg – including the GoPro. That’s about a kilo for the airframe, motors, controller, radio, ESCs, cables, props and landing gear. Looks like the electronics tip the scales somewhere around the 200g mark! There are acres of space on the new carbon body too. I hope it flies well because I’m itching to say I love the H-copter design, I just don’t want to count my chickens before they fly… or whatever.

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All that’s left to do now is wire the ESCs to the control board (bit of soldering required because I snipped the plugs off) and flash the KK board with the Quad-X firmware. I might also make up a set of spare legs to take along for the first real test flight.

Frozen in Carbonite

Wooo!  My parcel of carbon fibre bits arrived from HobbyKing yesterday so I shot out to the garage straight after dinner to start playing.

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Inspired by “The Firegoat” I decided to knock up a quad frame.  I have just enough motors to have a quad and a tricopter in service at the same time and I’m interested to play with the “H-copter” design that popped up on FliteTest recently.

Stability and high capacity are the plan for this one.  The design more or less mirrors the H copter Josh built.  The only difference is that I have used carbon and he used wood.

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One thing I learned pretty quickly is that carbon fibre – especially the 10mm square bar  – can’t cope with compression very well at all.  I used washers and didn’t tighten anything up too far.  The next picture shows what happened when I tried to bolt on the motor mount…

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The motors have to be pretty tight to keep them from spinning round or wobbling but as the photo shows, they can’t be bolted down.  So, I made up four “plugs” which poke 20mm into the end of the legs and prevent the nut and bolt compressing things too far.  They should add some strength around the joint too.

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One obvious annoyance with a quad as opposed to a tricopter is that you need to make four of everything!  The plugs weren’t hard as such, but it took about 15 minutes to get them made up and got quite boring.  Well worth the effort though – they do a good job.

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It was midnight before I shut up shop and I had a basic frame made up.  Four motors with 11×4.7 props with mounts stolen from the now-dead double tricopter.  No electronics yet, so tonight there’ll be much soldering in the garage I should think.

Complete with a 2.2Ah battery and with motors and props fitted the new Carbon Copter weighs just 800g!  With the GoPro on the scales it’s just under 1kg.  The lightest tricopter I ever managed was about 1.1kg without a GoPro and had (obviously) less thrust.  So I have high hopes for this little puppy.

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It’s traditional to end on a low, so I’ll do just that.  Carbon fibre is brittle.  I decided to do a little crash test with the motors attached – dropped the frame sideways onto the concrete floor of the garage from about 18″ up.  There was a sickening crunch.  No visible damage, but one of the legs now twists much more easily than the others.  I can only assume that some of the fibres within the leg have come unstuck.

I think I’ll have to make up some spare legs for the first test flight, and work on some landing gear too.

Very excited to get this thing off the ground!

Double Tricopter Failure and Flight of the Firegoat

Popped to the Green last night to test out the 6-way tricopter from my last post.  Something was horribly wrong with the control system and after the second massive crash an arm snapped off.  I doubt I’ll bother to rebuild the stupid thing!

The second crash also took a blade off “The Firegoat” – Dr Johnson’s newly completed quad.

Flying a quad is a totally different kettle of fish.  Much more docile and easy to control it just hangs about in the air.  The tricopter is very much more acrobatic – able to spin 360 degrees in about a second and with (I am told) a very helicopter-like feel.  The quad feels slower and more docile with very sluggish rudder… perfect for learning to fly, carrying a GoPro and learning FPV.

Inspired by this, and the never ending quest to minimise weight, this month’s man budget went on a selection of carbon fibre tubes and sheets to make a quad and hopefully Tricopter 4.0.  The 6-Way project will be “put on hold” for now I think!