Wednesday, 20 August 2014

Pi Wars

I'm thinking about entering Pi Wars in December. It's a Raspberry Pi based robot competition.

So far, I've scrounged a few bits and pieces, and put together a really basic remote control system using a Playstation 3 controller, an L293 H-Bridge driver board and an Arduino. The Raspberry Pi can do PWM and USB/Bluetooth, so it can take the place of both the laptop and the Arduino, when I get that far.

There are a few bugs, as I mention in the video, related to input handling. Basically if I play with it too much, the motor gets stuck (usually at maximum speed) and I appear to stop getting events from the joystick char device. But for now, here's a short video.

Saturday, 16 August 2014


And now for something completely different.

Someone asked the question the other day - what's the CO2 cost of the concrete in a Wind Turbine?

You need 1000 tonnes of concrete to install a wind turbine
You create a total of 410 kg of CO2 per m3 of concrete
Concrete has a density of 2.4 tonnes per m3
=> One wind turbine requires 416 m3 of concrete
=> You can attribute 170 tonnes of CO2 to the wind turbine's concrete

Assume a turbine base lives for 20 years.
Assume the turbine generates 2MW watts max
Assume an average utilisation of 30%
=> in 20 years, the turbine will generate 105.2 GWh

=> concrete production adds around 1.6 tonnes per GWh (Or 1.6 grams per KWh) to wind power.

If you make electricity using an fossil fuel power station, you create:

Coal: 910 g/KWh
Gas: 390 g/KWh

(The UK average across all fuel types, including renewable and nuclear)
is 470 g/KWh.

So, the effect of the concrete on CO2 emissions is negligible, compared
to traditional power plants.

As an aside, if your electric car requires 120 V / 15 A for one hour to
get 8 km of charge (these are the numbers for a Tesla Model S), you use
225 Wh of electricity per km at the wall socket. Given distribution,
that's about 240 Wh. Or, in the UK, 112.8 g/km of CO2. Which on a petrol
car is around 58 mpg.

But it's not that simple as that's only at the tailpipe and doesn't
account for refining and transport. A rough figure would be 6KWh used
per gallon of petrol in refining, for example, which is all coal based
in the UK

6 KWh per gallon of petrol
910 g/KWh for coal power
=> 5.46 kg/gallon of petrol

Assuming 58 miles per gallon of petrol (from above)
=> 94.1 g/mile CO2 emissions for refining petrol (consumed at @ 58 mpg)
=> 58.8 g/km CO2 emissions for refining petrol (consumed at @ 58 mpg)

This increases to 136.5 g/km at 25 mpg, on top of the 261 g/km the car
produces. Basically, add 52% to the tailpipe CO2 to compensate for the
refinery process. Plus a bit for the truck to take it to the petrol
station, and the ship to take it to the refinery, and the well to dig it
out of the ground.

So how many mpg does your petrol car actually have to do to match a
Telsa Model S for CO2, accounting for refining (but not transport)? 88