AGM #2

Also, cookies were had!

PCR Machine Hacking:

Ok, so we were sitting around thinking about our microwave. You’ve probably come across hot and cold spots in your microwave before. But where are they located, and how can we figure it out?

Well, we figured that a good way to do it would be to use the microwave to heat something, and then image it with a thermal camera.

The photo on the right shows the microwave, with the target removed to be run under cold water between runs.

Ingredients:

• 1x Microwave Oven (duh)
• 1x Ordinary HDPE breadboard, that you don’t mind cutting up a little
• 1x Ordinary A4 piece of paper
• 1x Ridiculously expensive thermographic imaging camera, borrowed (Seriously. This cost about twice as much as my car did.)

Mixing:

Thermal Camera:

Ok, so the first rule to bear in mind is this. Thermal cameras will lie to you. I’ll say it again. Thermal cameras will lie to you.

There are two ways in particular that I’ll cover, although there are a few more. Professional thermographers have an accreditation process and lots of training before they sell their services.
Let’s take the photo below. There are two ways in which the image of yours truly enjoying a frosty beverage is inaccurate:

The first is that the scale of the image is only set from 12.1*C to 35.8*C. So Anything outside that region will not be displayed correctly. This isn’t too bad, and anyone who works with graphs or scientific images will expect that.

The second way that the image will lie to us is that the measurement of the object depends on the emissivity of the material it’s made from. If you try and image shiny metal objects it’ll mostly capture the infrared light that’s been reflected off it, instead of the light it gives out iself. The emissivity of aluminium is about 0.09. So that means it’s mostly reflecting the temperature of the room behind the camera, instead of the can itself. The emissivity of paper is 0.93. So that’s pretty good as a target for our imaging.

Microwave Stand:

We used a layer of wet paper to absorb the microwaves and get hot for us to image. In order to hold it upright we made a stand out of an old breadboard.
According to this, HDPE is listed as ‘may be’ microwave safe (I’m not entirely reassured…). So we’re assuming it’s not absorbing the microwaves too much.

Before each run we carefully ran the target under cold water for 30sec to a minute. This was necessary to make sure it was a uniform temperature across the whole plate. We then microwaved the plate for 10 seconds, and observed the temperature through the camera.

Results:

Arghhh… I hate wordpress images!  It won’t display them nicely.  Check out the results here, if you’d like to see details:

https://sites.google.com/site/mechatronicsguy/coolthingoftheweek/microwave-hot-spots

Replication:

So the question is naturally raised, how repeatable is it? Are the patterns random each time, or is it determined by the position in the oven?
So we ran the same position twice. And between each run we fully removed the target and ran it under water to cool it down to a uniform temperature, replacing it back in the same measured position in the oven.

So, we’ve got a really nice, repeatable result for where the hot spots are in the microwave. Does this mean that we can now put in our hot pockets in the optimum spot, safe in the knowledge that it’s perfectly scientifically validated?

Well, sadly not quite. Putting an object in the microwave will actually change the standing wave patterns, since it’ll absorb and reflect microwaves.

Still, it was interesting to gain an insight into what’s normally an automatic process.

Bonus: Makerbot Thermographic Porn!

At the same time we were doing the microwave experiment, Chris & Max were assembling our new heated build platform for the makerbot. So we thought we’d get some shots of it in action…

I was quite suprised how hot the extruder controller got. You can see the max temp is 68*C. (Sorry for the shoddy scaling in the image, anything over 35.8*C is saturated. The maximum is reliable, though)

Each week we’ll build a project, tweak something or set something on fire and report on it to you. And as Adam Savage says “Failure is always an option”. We’re not guarranteed to figure it out, or even get it working. We’re just going to hack stuff together (or apart) and have fun!

If you’ve got any ideas you’d like to see as a CTOTW, please send it to us!

Installing the ADSL was an Adventure™. For starters, I had to wake up at 6.30am to get to the space by 8am, which was when TPG said was the earliest time the engineer might reach the house. I arrived with coffee and Subway cookies, and looked around for the phone socket.

Um. There wasn’t one.

I peered around the front of the house, and saw aerial cables from the nearby telephone pole (which I later found out were completely irrelevant — Foxtel or Optus cables). 15 minutes of searching for a torch later, I ventured under the house with a floodlight (overkill is what we do!). I traced the aerial cables to cables under the house (my hair collected about 40% of the cobwebs off the beams). There’s a 4-wire cable, but it’s been cut. Ugh.

Half an hour later, the TPG guy shows up and crawls under the house with me to look for the cable. Eventually we found it, poking up into the board room with no socket on the end. He tests it, and to his great surprise (and my relief) it works. Clearly the line hadn’t been used for years, and for it to still be connected and working all the way through to the exchange is a small miracle.

Somewhere in the junk room a Netgear modem was found, and a 12V/1A power brick stolen from the Linksys router. The modem was configured, and Internet was had.

And there were megabytes.

No longer will hackerspace-goers be plagued by the lack of data or the irritatingly long wait for Youtube videos! No longer shall we resort to our variously crappy 3G connections! At last, we are free!

Without further ado:

It’s just got back, and (in addition to being awarded a high distinction) they’ve kindly allowed us to post it on the net.

Robots And Dinosaurs — A Hackerspace Documentary

Big thanks to Lucy, Doug, Hamish & Edwina for promoting our group for us.

I tried to make a sheet that captured all the things I hit the reference for while programming. What data type does the millis() function return? How long till that overflows again? How large can a long get? What baud rates can the serial handle?

Any other things you’d like to see added, send me an email and I’ll stick them on Rev 3!

Edit: Just did some minor mods suggested by people. Here’s V.02b

Small version. Use PDF for printing purposes

Arduino cheet sheet v02b (PDF)

Editable visio version on my website:

http://sites.google.com/site/mechatronicsguy/arduinocheatsheet

]]> http://robotsanddinosaurs.org/?feed=rss2&p=300 1 http://robotsanddinosaurs.org/?p=269 http://robotsanddinosaurs.org/?p=269#comments Mon, 12 Apr 2010 04:12:54 +0000 gavin http://robotsanddinosaurs.org/?p=269 For those of you that haven’t been following, we attended Rocket Car Day 2010 on the weekend. This is an event where everyone cobbles/crafts/hacks together the most baddass vehicle they can, then crams a rocket engine into the back and competes for honor and glory!

Some people spent a lot of time on their cars:

K9 hero shot

Others less so:

The K-t event

Unsurprisingly at such a geeky event, RnD members were there in full force. We even had our own race!

(Note the swanky new lab coats, with RnD embroidery )

The RND possee and their cars

Here’s a couple of videos of the cars:

Sorry for squealing at the end of the vid, but I really wasn’t expecting to win against those other cars which were, frankly, better than mine

Special shout out to Big (Iain) who made his own custom arduino & digital compass powered car! We were all sorry to see it was short lived.

Big's guided car

Beco blocks are great as toys and i suspect might also find practical applications for things like:

• Light duty hinges.
• Printable helping hands
• Internal skeletons for soft toys.
• Snap together bracelets.
• Mini pose-able art mannequin

Beco blocks thus far have been printed on our Makerbot using ABS plastic. The first Beco block printed was very lonely, being the only Beco block in existence with no friends to snap together with. Some time later when I finally learnt how to use the Makerbot myself I started printing more, and was surprised to discover how effectively they clicked together. There were practically no design iterations in making the original male-female Beco block, i was just very lucky with a ball and socket size ratio which seems ideal.

The 3d models for Beco blocks include struts which allow the printing of the ball in a horizontal orientation. The struts can quickly and easily be clipped off using light wire cutters.

There is plenty of room for improvement in the design and additional brick variations. I have only designed enough types of bricks to build a basic figure so i hope others add to the collection.

The STL files are available at Thingiverse here: http://www.thingiverse.com/thing:1983

• We built a hot-wire foam cutter for the space, which should come in handy with our upcoming drumkit workshop.
• Playing around with the BlueBoards we got. Congrats to Kean for solving the downloading problem.

Congrats to everyone for pledging for our new CNC Machine! We’ve reached our target in under 24 hours! I’ll put in the order tonight, and we’ll get this beast to us ASAP.