Freesteel Blog » 2015 » August

Wednesday, August 26th, 2015 at 1:24 pm - - Whipping 1 Comment »

If voting changed anything, they’d make it illegal — Emma Goldman.

So, if you want people to vote, they have to believe that it can change something.

The Labour Party is undergoing a sudden and spectacular revolution with hundreds of thousands of people signing up on the belief their vote will make a difference when they elect Jeremy Corbyn. No one saw this coming.

Just one month ago the former leader Tony Blair said that anyone who supported Corbyn should get a heart transplant.

Funnily enough, Blair only became party leader (and, by default, Prime Minister) because John Smith had a heart attack and died. Blair was then stupid enough to believe that he was there because of his awesomely crappy policies that caused so many people to quit the Labour Party he had to fund his 2005 election by selling seats in the House of Lords.

Voting in Scotland in a referendum was going to make a difference, and the turn-out there was massive.

But in the wider country there continues to be a problem with General Election where necessary change is not coming about and people are getting screwed.

Young people don’t vote because they know it doesn’t make a difference. The system is too skewed. The old people in the rural constituencies reliably root for the Tories and provide their base. The Tories return the favour by redistributing the wealth from the youth to their elders on a massive scale through rising house prices, tuition fees (after this older generation got educated for free), historically low wages, a rising retirement age, a declining pension (which doesn’t effect the current generation of pensioners), expensive public transport while car driving becomes cheaper, cuts in inheritance tax (how old are the “kids” when they actually get the money?), and huge bank bailouts to protect the savings of those with hundreds of thousands of pounds on deposit.

Wednesday, August 19th, 2015 at 6:44 pm - - Machining

The limitations of the scipy.optimize.minimize() function has now become apparent. They should have called it localminimize() starting from an “initial guess”.

This follows on from the mess I made out of using this same function to calculate the circumcircle of a triangle.

Here I begin with a STL file of a widget which was then probed from 20 random directions to a distance (ball radius) of 5mm.


This was done using a my barmesh library that I ought to start getting back into as I haven’t touched it since I got distracted by all this arduino electronics.

The barmesh code itself is impenetrable when I looked at it recently, but use of its features is still possible.

Thursday, August 13th, 2015 at 5:27 pm - - Flightlogger

I’ve got a Global Top Inc FGPMMOPA6H GPS module (datasheet) in my hang-glider data logging device. Using the command packet:


I’ve programmed it to give me a GPRMC every 50 cycles, a GPVTG every cycle, GPGGA every cycle and a GPGSA every 10 cycles.

The command $PMTK220, 200 is used to set the length of the cycle at 200ms, so I’m getting a positional and velocity reading 5 times a second.

The code for controlling all this is here. Note that my code does not contain hundreds of lines of #defines of the form:


that you tend to get in other people’s programs for the purpose of referencing the this-will-never-change-hardware-encoded 3-digit string ‘314’ by the arguably more readable (ie I will argue with you) string ‘PMTK_API_SET_NMEA_OUTPUT’ that serves no purpose, isn’t interpreted by anything except the preprocessor, and you have to look it up to get back to the number that is actually documented in the manual. Why is this controversial? </rant>

Monday, August 10th, 2015 at 5:24 pm - - Machining

I failed to take a photo of the experimental set-up which the guy on the Newcastle stand at Manchester Makefest let me shove my airspeed probe into. The airspeed probe is described here and some interrupt timing misery to do with it (which I don’t know was properly solved) is reported here.

This is the track of the windspeed when it’s in the device, and then when we put a card across the air intake that roughly halved the flow.
The time interval is 5 seconds for every green vertical line.

The readings where it is flat and high (off the left of the diagram) have an average of 7.11m/s, standard deviation 0.11 over 60 seconds. The middle low section has average 3.26, sd=0.05 over 35 seconds. The final high value when I took the card off the intake was 6.99m/s, sd=0.077 over 45 seconds.

The tailing off of the wind speed measurements is probably an important factor.
Squashing the graph down the Y-axis and plotting the green lines at one second intervals, we can compare the two incidences where I put a card over the intake and halved the wind flow.

It takes about one second to settle, and the two curves don’t match up.

I can’t tell if this is due to the inertia in the propeller sensor, or inertia in the wind tunnel device when I cover it up making it sound like a blocked vacuum cleaner.

At least half is due to the latter, or the curves would be a better match because they’re smooth enough and the propeller inertia doesn’t change.

We’d need another way to more quickly vary the intake into the wind sensor. For example, we could rotate it slightly so that it picks up less wind. The engineer suggested introducing some controlled friction into the system to dampen the spinning so it responded faster. Alternatively there’s a pitot tube.

Of more immediate concern is the unexplained wandering around of the wind speed sensor by as much as 6% across multiple seconds of time. This can’t be turbulence in the device as it wouldn’t have such lasting effects.

Also, there are short bursts of zig-zagging every half second indicated by the red marks.

I’ve seen these zigzag effects before with the temperature measurements, probably caused by the interference with other devices on the same microcontroller, going into and out of phase with their interrupt cycles.

I don’t know of a mechanism for voltage changes to affect the rotating fan blades (like they did the thermistors), although something could be introducing small delays into the detection of the interrupt signals.

This would take a lot more building of separate interrupt-driven dedicated microcontroller circuits to test the theory. And then that doesn’t answer the 6% wandering.

I got to get back to other parts of the project, and look at this later when I have use for these measurements as well as a test rig.

Maybe there’s other technology, such as a thermal anemometer or a beautiful sonic anemometer that measures windspeed and direction instantaneously for a mere $2700. I haven’t got that kind of money to squander at the moment, but it does show what’s available.

OMG, what’s this publication I’ve just uncovered:

Sonic anemometer and atmospheric flows over complex terrain: measurements of complex flows

Three measurement campaigns and the use of sonic anemometry under specific conditions are described in this work. EBEX2000 was an international energy balance field experiment in San Joaquin Valley USA, were different sonic anemometer types, and heat and momentum flux measurements, were analyzed and compared. The second case was a complex coastal flow at Madeira Island, Portugal. The complexity of the flow compromised the performance of an existing wind farm. The use of post-processing techniques, such as Fourier and wavelet spectral analysis allowed the detection, and unveiled, the existence of coherent structures and other specific features of that wind turbine site. The flow over the mountainous terrain of Madeira Island is also presented for the latter case, where sonic anemometer measurements were executed at wind energy resource assessment phase.

I found some excerpts of the book where they are discussing the instruments. Taking some liberties with the text, there is:

As discussed in chapter 3 the sonic anemometer measurements have to be corrected due to transducer shadow effect and overestimation of measurement due to flow acceleration through the transducer array…

The cup anemometer systematically overestimates the mean wind velocity compared against the sonic… Wyngaard (1981) showed that cup anemometers respond faster to wind speed increases (u > 0) than wind speed decreases causing the anemometer to overspeed.

My anemometer is a propeller, which requires it to be pointed in exactly the right direction. This is not going to help when there is yawing of the glider of up to 80 degrees.

The interesting thing about atmospheric flows over complex terrain is that good glider pilots have the experience to guess the locations of up-currents by visual inspection and from what they know of the wind direction.

In the future the swarms of cooperating autonomous cargo gliders which connect the world together using zero energy (unlike the plans for drones) will be able to not only rely on thermal updrafts, but could also use dynamic lift by reference to weather stations dotted at critical places around the landscape to inform the flow model accurately enough to fly downwind with exactly the right height to clear the next tree line.

I’ve got to climb out of this rabbit hole now before it sucks me in for the rest of the week.

Monday, August 10th, 2015 at 3:14 pm - - Kayak Dive

What do you do with someone who broke their elbow six weeks ago?

Take them on a long 7 hour canoing trip up the Conwy river from the coast at Deganwy to the new inland surf station at the historic village of Dolgarrog, of course.


Due to the lack of a waterproof camera, I don’t have any photos of our journey and of the many hours upwind paddling through miles of waving reed meadows and into the small dry creek leading to the hydro power station.

We parked on a bank full of thistles and waded through stagnant pools and along rocky river beds before we reached a road bridge where we could climb up and over the fence.

Down that road was the surf pond, already packed out on its 6th day of operation. We had our picnic on a bench watching the surfers, noted that it was already half past six, and then rushed back to the boats before we got benighted.

In the meantime the hydro power gates had opened, causing a slightly worrying river crossing. The tide had also risen another metre (more than an hour after Conwy high tide at 5pm) nearly washing our boats away.

More engineering

Last Thursday I made a trip to the Advanced Manufacturing Research Centre in Sheffield. It’s a bit of a massive establishment with a lot of machine tools, so they ought to have people making special CNC toolpaths for them. On the other hand, I don’t think the development of yet more passenger aircraft technology is necessarily a good investment of engineering resources, given that the industry needs to shrink by 10% per year from now on as part of any strategy for us to survive on this planet with our species and civilization intact.

I decided I need some mechanical engineers to put to work on the triangular machine tool, and formed a theory that there were not enough of them around because they’d all got a proper formal education which put them on the conveyor belt into corporate employment where they were no longer an accessible resource. On the other hand, software engineers are often self-taught and therefore don’t begin their careers with much faith in the system, and so tended to be easier to entice into random start-ups that don’t have any rich person’s backing.

Then I spent most of my Sunday in Manchester at the MakeFest in MOSI not helping on the DoESLiverpool stand at all. But I did find plenty of mechanical engineers who immediately contradicted my theories.

One of them had made a tiny wind tunnel model into which he let me insert my hang-glider wind meter for testing, which I’ll talk about in the next post rather than confuse everyone by putting at the bottom of this page here.

Monday, August 3rd, 2015 at 11:40 am - - Machining 1 Comment »

We will begin today’s rant (following last years post-quitting blog) by turning to Carl Bass’s favourite management consultancy firm, McKinsey&Company, and searching for “Autodesk” through the link:

to get 17 hits — 10 of which are for exactly the same page.

Well done McKinsey. I hope your internal document management system is better than the one on your webpage, given that your only purpose is to write commissioned documents.

The McKinsey article begins:

How big companies can innovate
Who says innovation is only for start-ups? In these interviews, the heads of three large, established companies — Intuit, Idealab, and Autodesk — argue there’s no reason big players can’t develop the next big thing.

First up is Carl Bass. What’s he got to say?