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.


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.


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