Month: February 2016

Factors of Four

Just as I predicted last week, I’m too busy with work to go flying, but it would have been difficult anyway with the strong Easterly wind that’s blowing this morning.

I’ve been soldering rather a lot of small quadcopters for an event that we’re running next week:

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Four almost complete HubSans (top row), with the fifth left unmodified. The flight controllers and motors are in the next row, with the white 3D printed frames next and the four sets of flight controller wires at the bottom. The left most white frame (ghost) contains the HubSan prototype making up the first of the 5 custom conversions. The butterfly second from the left is using my own HubSan kit which was the initial proof of concept.

What we’ve done is to take the electronics out of the HubSan X4 H107C (camera version) and add plugs and sockets to allow the motors to be removed. Then we’ve put the HubSan flight controller into a custom 3D printed frame. The HubSan X4 H107C only cost £32 each on Amazon as we got the 0.3 megapixel version which has recently been superseded by the 2 mega pixel version.

The picture shows the current progress before the sockets have been added to the flight controllers and before the plugs have been added to the motors. We actually have 6 HubSans, with the prototype already modified and not in the picture, the four HubSans here are part way through modification, and the sixth one on the right of the picture we are going to leave unmodified. If you count up the number of soldering operations required to do this, then you can see why I’ve been at it all day. Also, in the later pictures showing the completed work, it’s obvious that it’s got dark while I’ve been working and the picture is in artificial light.

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Four modified HubSans with all the connectors attached. The picture is yellow because it’s quite dark by this point and my lighting is not very good.

So that’s 5 quadcopters modified as follows:

  1. Disassemble HubSan, remove rubber feet, props and de-solder camera.
  2. Remove 8 LED connections to flight controller.
  3. Remove 8 motor connections to flight controller.
  4. Remove 4 motors and flight controller.
  5. Solder 8 sockets onto 4.5cm wires (red+blue, black+white) and solder 8 wires with sockets onto the flight controller. Apply 2cm of heat shrink to each socket.
  6. Solder 8 plugs onto the two wires from each of the four motors. Apply 1.5cm of heat shrink to each plug.

Counting up, that’s 5×16=80 wires to de-solder, 5x(8+8+8)=120 solder connections to make. All divisible by four. Thank goodness I didn’t have the stupid idea of making hexcopters instead.

Anyway, it’s all done now, so I just need to check that all the electronics still works. I’ve checked the motors using a 4 cell NiMH pack to verify that all 20 run. The only real way of testing the flight controllers is to put them into a frame and connect the motors, so I’ll do that over the next few days.

One thing worth mentioning is my use of salvaged connectors for the motors and flight controllers. I had initially been using square DuPont connectors (Futaba servo plugs) with standard square metal header pins. At this size, they are a bit fiddly to connect, with the two pins connected to the motors not being as mechanically secure as I would like. My solution was to buy a 25 way D plug and socket from Maplin and remove the metal pins.

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How to make 1mm bullet connectors – open up a 25 way D connector and salvage the pins.

I’ll do a follow up post on how to do this, but the pins and sockets make really good connectors for small models if you solder wires to them and then cover with heat shrink. It’s like a micro version of a bullet connector and, being round, they’re really easy to push together.

That’s all for this week as I need to get back to work making some more frame designs for us to 3D print. I’ve taken lots of images of the process though, so I’ll post more once I’ve had time to do the video editing.

Still Windy

The weather wins again this week. It’s already very windy and they’re forecasting gusts up to 35 MPH later in the morning, so there’s no flying again this week. I’m not sure whether I’m going to manage the next two weeks either, as we’re running a Royal Institution Coding for Year 9s session at work in a couple of weeks and need next weekend to build 6 micro quadcopters with 3D printed frames.

I did manage some flying indoors and in the office during the week testing the micro quadcopter kit:

It really is in quite a tight space and I’m conscious of all the wires hanging off and the fact that I can’t afford to crash our only prototype. It’s also quite badly warped where we tried to clean the 3D printed PLA frame with water. The warping seems to be most of an issue when you try to rotate with the rudder. It was just drifting badly all over the place, although that could be the fact that the flight controller is held on with elastic bands. I even had to wrap sellotape around the motor cans to make them a tight interference fit in the 3D printed holes, which aren’t printed very accurately. We had a go in the office at work as well, but the frame is rather heavy, so I’ve been trying to design a lighter version.

Sourcing micro quadcopter parts in the UK is really difficult, so we settled on the idea of taking the HubSan X4 commercial product, removing the motors and flight controller/brushed ESC and fitting it all into our own frame. Economically it works really well as we can buy a HubSan X4 set off of Amazon for around £35, which contains everything we need including the USB charger and 2.4GHz transmitter. It’s just a shame that we can’t reprogram the flight controller software, but you can’t have everything.

I’ve been using FreeCAD to do the frame design, but it is a parametric modelling package, so it’s really difficult to get started with. On the plus side, I’m not very good at drawing things and this requires objects to be defined in XYZ positions, so I can type in where I want the component parts to go. With a bit of mental arithmetic and fiddling with the position in FreeCAD, I can stick four cylinders at each corner, turn them into pipes for the motors to fit and attach an H-frame made from flattened cubes. It’s all constructive solid modelling, so you fuse objects together and cut bits out to make shapes. It’s a bit quirky to get the hang of, but I’ve managed to create an H-frame which should weigh less than 8g.

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My H-frame for a micro quadcopter (100mm) built in FreeCAD and ready for 3D printing

Once the design is complete in FreeCAD, I can export it as an ‘stl’ file and load this into the MakerBot Replicator software to test how it will print. By doing a ‘preview’ print, it calculates how much material will be used and gives you an idea of the weight. From the two other designs that we’ve done so far, it looks like the weight comes out a little bit higher than the final 3D model. You have to allow for the addition of rafts and supports which will be removed from the frame’s final flying weight, but even so, I think it still estimates the material a little high. It probably depends on the density of the PLA though. Anyway, it’s going to get printed tomorrow, so we’ll just have to see how it comes out.

That’s really all I’ve done this weekend apart from adding the tail skid to my ATOM Autogyro which is currently setting. It’s propped up at a really precarious angle, so I can’t post a picture of it just yet. I’ve also been painting the pilot and trimming the canopy to fit. I’ve made him a little pair of glasses and will make him a baseball cap later. This is mainly to disguise the fact that I’m useless at modelling pilot figures, so will hopefully end up with a sort of cartoon pilot in the end.

Weather Again

It’s quite bright and sunny this morning, but there’s a strong northeasterly breeze which means that it’s not worth venturing out of the house to fly. I’m also grounded for other logistical problems and have a mountain of work to catch up on before Monday.

Despite this, I’ve made some more progress with the autogyro, to the point where I’m now looking at it thinking, “what do I still need to do before I can cover it?”. The pictures should give an idea of the current state of progress.

I’m currently making the tail skid as you can see that I’m having to balance the back end on an old 2v glowplug battery. The weird thing is that part of the balsa skid had been cut off, so I must have thought it was scrap 6mm balsa at some point and cut the top off to make something else. Now, not having any more 6mm sheet to hand, I had to find another scrap and stick it to the top to make a complete piece. The fibreglass bit is going to get stuck on soon, after which I can attach it to the underside of the tail. The aileron and elevator rods all work, but I’m still in the process of trimming the canopy so that they can poke out of a hole. Carefully and little bits at a time is the way to do this so I don’t cut too much off. I just keep fiddling with it and gradually improving the fit until I’m happy with it. Also, the pilot needs painting, so that’s something else I can do.

Last weekend I spent far too much time on the quadcopter simulator which we’re going to need for a workshop in three weeks’ time. It’s about ready for release, once I’ve done a few final tweaks. I’ve also ordered a replacement PCB for my HubSan X4 which is currently sitting in a custom 3D printed frame. That’s due to arrive next week, so I should be able to resurrect my little HubSan in another body.

Hopefully next week we’ll get some better weather.

Ripples in the Grass

It’s a lovely sunny morning, but it’s so windy that you can see waves being created as the wind blows the blades of grass in gusts. Yesterday was even worse with 50 mph winds, so I wasn’t expecting to do any flying outside this week.

I know I said I was finished with quadcopters for a now, but events turned out slightly differently. We have a 3D printed frame for a micro quad that I need to build for work, so I spent Friday evening cleaning up the 3D printing defects and Saturday de-soldering the PCB from my broken HubSan X4.

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The 3D printed frame and four 55mm props for scale. Diagonals are 100mm.

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With the motors added.

After lifting the PCB out of my HubSan and soldering 8 connectors for the motors, the final result looks something like this:

I’m very happy with the result, apart from the fact that my HubSan elctronics just refuses to work. I knew this before, which was the reason why I was willing to transplant it into another frame for a test. Sometimes it would work fine, then die as soon as you spun the props, and other times it worked perfectly. In other words, intermittent. The trouble is that I can’t get it to work at all now, apart from a brief glimpse of life last night. It must be a cracked PCB or bad solder joint somewhere, but I just can’t seem to fix it. Anyway, when it did come on I proved that there was enough power for it to fly when it flipped over and tried to take a chunk out of my finger. That’s what I like about this size of quad. It feels like it’s powerful enough to damage your fingers and it hurts, but it’s actually perfectly safe. Just what we need for a bunch of 13 year old students.