Saturday, 22 November 2014


So after a lot of talking about it and a lot of time making sawdust and wood-shavings in the shed, I finally feel as if I've made enough progress on this to bother to put some pictures up about it.

The original idea was just to have a go at making a cello, but it has drifted into the idea of making a cello out of wood from as close to home as possible. This mainly happened because there was a fairly big Sycamore in our back garden that was shading everything out and when I felled it it was pretty sound inside and big enough to get a one-piece cello back from. I'm hoping to get a piece of willow that blew down in last year's storms on campus, but I'm still waiting for it to get sliced up (and it's not as close to home as the Sycamore).

So here are some of the lumps that came from the tree:


Not very subtle slices were hacked out with Ieuan's chainsaw and then planed down to make a slab suitable for a back:


I marked out a (fairly over-size) cello-shape from the plan that Mick-the-real-luthier-De-Hoog sent me (thanks Mick!). Then spent a few hours whittling away at it to get a feel for the quality of the wood and how it would shape up. It was quite fun getting the basic shape and profile:


Having done all this (good fun) whittling I realised that actually I should have been making the ribs and middle bit first and that I was just putting it off because it looked hard. So I started out by making a former:


I made it from a sandwich of plywood and spacers held together with screws so that hopefully when it comes to time to get it out it will be easier than doing it in one piece. Then I asked Matt-the-man-with-proper-tools to slice up one of the bits of Sycamore that I had crudely slabbed and he provided me with a nice pile of rib material around 2.3mm thick. I then spent a jolly day in the shed with a plane, belt-sander and set of cabinet scrapers to get them down to the recommended 1.5mm. After lashing-up a bending iron from an old piece of boiler pipe and a hot-air gun:

 I was ready to bend the ribs. The boiler pipe is about 3mm wall thickness and started out as ~5in diameter. I crushed it in the vice to get curves that looked about right for a cello and then almost blocked the end with wire-wool to keep the heat in and it worked surprisingly well for bending the ribs with the hot-air gun running whilst I worked. Had to be a bit careful to avoid burning too many bits of skin, but no trips to casualty yet and just a gentle aroma of singed hair.

So after chiseling and gouging out the blocks and bending the ribs, this is what it looks like at the moment:


Close-up of one of the C's:

Not a perfect fit, but close enough to pull in gently with clamps. That's the next step, think I'll do the pieces one at a time over a few days. The blocks are glued to only the top layer of the former with deliberately bad joints to try to make it easy to chisel them out when the time comes.

In the mean time, I stole one of Ieuan and Elizabeth's Sitka Spruces to use for the sound board. I took one from the edge of a bog which had stunted its growth a fair bit, so the rings are fairly close together. Not big enough to do a single piece, or even two piece soundboard though, so may end up being three pieces glued edge-to-edge. The Sitka logs:


 The Sitka was the furthest from home that we have had to go (about 400m).

Hoping to get a fingerboard and pegs out of some pieces of hawthorn that I cut down earlier in the year. Not sure how it'll be to work with, looks pretty dense and hard, but we'll have to wait and see:

The Sitka has been sitting in the shed for a couple of weeks now, so I need to get it sawn up (properly this time) and then give it a good few months to dry out before trying to do anything much with it, so don't hold your breath on an update!

Tuesday, 13 May 2014

Ysgol Gymraeg Prosiect Gofod (High Altitude Balloon)

I won't even try to do this in Welsh, sorry! If anyone feels like translating it that would be great...

So we're trying a High Altitude Balloon launch from Ysgol Gymraeg Aberystwyth sometime soon, and I've been tasked with getting the bits and pieces together for the launch. I started off with a "keep it simple" attitude, and I've avoided having any electronics in there that are home-grown. I've opted for a GoPro looking sideways, a simple GPS/GSM tracker and a smartphone looking down (and providing back-up tracking). I went for a Hwoyee 1000 balloon (which is almost certainly overkill) to let the kids have some payload left for a cardboard construction around the main payload capsule which is going to be a hollow polystyrene sphere.

So far I have most of the bits together:

Payload capsule halves

And the two halves slotted together

GPS/GSM tracker

The polystyrene sphere is 250mm diameter and came from Ebay for a few pounds (I bought two because they looked so useful!). The tracker was also from Ebay and is basically a cut down mobile phone. If you send it an SMS or call it it is supposed to send you an SMS back with its latitude and longitude and a link to its position in Google maps. I haven't yet installed a SIM and tested it... soon now. The balloon and parachute came from who have a good range of stuff on their site.

I knocked up a spreadsheet of weights (click to view):

The long and the short of it is that with the 1000g balloon we are going to have bucket loads of lift to spare which should mean a good fast ascent and hopefully the balloon will land within a sensible distance of the launch site.

This site has a nice calculator for ascent rate etc...

And this one does trajectory estimation using the ascent rate from above (I'm working on ~6m/s):!/uuid=e9dc794115cc0c3d5b94ecf4d6d40dcdfcb442b8

Aberystwyth's latitude and longitude is around 52.4N 4.1W (remember that West is negative for longitude).

I need to do a little engineering to mount the GoPro and phone and I think we're supposed to be doing a parachute test with a realistic payload so a nice exercise for the kids might be to weigh and measure the internal components and make models of the correct size and weight to put in the dummy launch which will stop us from breaking the real ones in the test (and might even be a little bit educational).

9th June 2014 update:

So I've been a bit slow updating this, but there has been lots of progress!

I have now tested the GSM tracker above and it seems to work a treat. It ran for just over a week on the dashboard of one of our cars and had an accidental trip to the Eisteddfod in the meantime. I can call it from my mobile and it sends a text message with the latitude and longitude and a link to the location in Google maps. I have also put a SPOT tracker inside the polystyrene sphere and checked that it can transmit in tracking mode and it seems to work fine.

We are aiming for launch this Thursday, and it looks pretty good at the moment with light Westerly winds meaning a fairly short drive for the recovery team.

The capsule looks like this with the GoPro and phone (cheap Orange Stockholm):

And like this in the inside:

(I may use something other than sticky tape for the final release, although I might just upgrade to gaffer). The whole assembly will look like this, but hopefully with a cool cardboard and paint rocket built around the sphere:

I started the project with a "no home-brew electronics" rule, but I may have broken that now... I'm thinking about putting a moteino (very cool!) with an accelerometer, gyro, magnetometer, thermometer and altitude sensor in there. The moteino has a built-in 433MHz radio transceiver, so that would allow me to have a down-link during the early part of the flight. I may be up late on Wednesday night.

Launch conditions for Thursday look pretty good, and the trajectory prediction says it will come down somewhere near Llanidloes:

Fingers crossed!

10th June update:

So after a little high quality engineering from blwyddyn pedwar and Mr Jones (see for mug-shots of those concerned) the capsule has been converted into a full-on inter-planetary spacecraft:

... which is proudly displaying the logo that the children designed along with one or two of the school's sponsors:

So all the cameras are fully-charged, the trackers are set-up and ready to go and the helium is ready and waiting. What have I forgotten? I don't know... if I knew then it wouldn't be forgotten would it?! 

Weather still looks good for a touchdown somewhere around the Llangurig, Llanidloes, Rhayader triangle. I expect the flight to last a little less than 3 hours with around 1.5 hours of communications black-out when the balloon is too high for the GSM network to allow communication and when the satellite tracker is also above its rated communication altitude. It'll be a bit scary not knowing where it is for that long.

The last little frill I'm hoping to add is this:

... which is a moteino from with a GPS module and a "10 DOF" inertial measurement unit. Moteino's have a 433MHz radio module built-in and I'm hoping to find time tomorrow to write the code to relay live the position, temperature and altitude to a ground station. I have a nice big 433MHz Yagi antenna which should mean that we can receive data for the first few thousand metres of the ascent, but with no time to test beforehand it's a bit of a gamble, but adds a bit more fun to the whole thing. It works on my living-room floor, so it's bound to work at 10,000m isn't it?

11th June update:

So it's 11pm and I just finished the code for the moteino. It now logs the temperature, altitude and position in the on-board flash (in a format that I can recover sensibly) and transmits it as well. The ground station is a nice high gain (11dB) Yagi antenna with a second moteino wired in to it. No time for any software for the laptop, so it's just logging through minicom to a file for eyeball analysis. Despite it being a bit of a lash-up I'm quite pleased with how the receiver looks and works:

The black blob at the end is a heat-shrink covered moteino soldered directly to the antenna connection cable.

Looks a bit odd to have a USB cable coming straight off the antenna, but it seems to work quite nicely. It'll be interesting to see how much range we get from this arrangement.

And last but not least my very high-tech checklist (every project needs one). All ready and nearly 12 hours to spare!

12th June update:

We went down to the school this morning around 8am for radio interviews and set-up, all went well apart from it taking a long time to fill the balloon (around an hour!). I think I need to invest in a better filling mechanism... the payload was attached and the balloon was released (after the obligatory countdown) at around 10.45am. The moteino radio relay worked beautifully up to around 3,000m, and then we watched it for a further 15 mins or so as it disappeared into a clear blue sky. Then it was all very quiet... for a while... until around 1.30pm when we got a position back from the GSM tracker (don't ask about the SPOT!). So the recovery team are en-route to pick it up from a field a bit North of Llandrindod Wells. Hopefully some of the images will be worth having and I will try to post some tonight when I get the memory cards back. I'll also post the data from the moteino if it's worked properly. Watch this space!

Picture I stole from Hannah taken just before launch.

And away she goes...

13th June update:

So after a bit of a drive and some wandering around Emma and Nic and the children found the almost completely undamaged capsule (pic to follow sometime). I then spent about 10 minutes trying to open the GoPro case (it was "full" of vacuum), which involved prodding the sealing rubber with a knife to allow air to re-enter the case. Then I took the images off... Wow! Some really amazing ones. Please feel free to use the images, but I would appreciate it if you make sure to credit them to Dr. Mark Neal, Aberystwyth University, and ideally to mention Ysgol Gymraeg Aberystwyth too:

First image after lift-off

Looking South

Aberystwyth University campus and Waun Fawr

Mid-altitude looking South


Looking North (Aberdyfi)

Higher altitude with nice black sky

The moment the balloon burst... we were amazingly lucky to get this shot! The parachute is still folded, and I suspect deployed fairly rapidly after this shot. Estimated altitude of 31,000 metres. This is based on data from the on-board monitors and the time elapsed after they failed (future post will describe the (badly corrupted) data that was stored on the moteino flash.

The whole of Cardigan Bay and hints of Eire in the background.

Looking South over the Severn estuary to Devon

I will post again when I've extracted all the good data that I can from the altitude and temperature log.