We are designing a camera + light-source based localization system to let our robot localise itself in the Eurobot arena - see our other blog post for more details http://www.element-14.com/community/groups/mew-imperial-college/blog/2009/11/22/localization
One job is to make the light-sources, or beacons. Here are some things we considered:
- 3 beacons, 1 must have 180degree illumination, the other two 90 degrees.
- Red worked better in tests.
- Must fit in 80x80x160mm volume.
- Bottom has hook Velcro.
- Light must come from the same position horizontally no matter where in field of illumination the observer is (but vertical displacement doesn't matter)
- Shielding from lights on the horizon is desirable - the
- Flashing LEDs, frequency adjustable. Between 1-100Hz
One of the problems, is that normal LEDs have quite a small angle of illumination - typically 30-60 degrees. We require up to 180 degrees. Our initial idea was a traffic light style beacon:
Unlike a traffic light however, each of the lights will point in a different direction. Their fields of illumination will overlap to ensure that all of the arena is covered.
The robot, when navigating the arena, will then use its camera to find where each of the three beacons are, and use a little bit of maths to find out its current position.
Change of Plan!
Well, while this might have worked, we found another high power LED with an angle of 165 degrees! - http://uk.farnell.com/avago-technologies/asmt-jr30-ars01/led-3w-red-80lm/dp/171839. So we are going to try using these instead.
The new LEDs are surface mount packages which is a problem, since we only have experience and equipment to solder through-hole components. In order to solder these, we are going to build a soldering oven! Like this one - http://www.seattlerobotics.org/encoder/200006/oven_art.htm. We have ordered a Toaster Oven from Amazon - http://www.amazon.co.uk/Sabichi-83913-Mini-Oven/dp/B000L1KHYM/ref=sr_1_1?ie=UTF8&s=kitchen&qid=1263052699&sr=8-1 and some solderpaste from Farnell - http://uk.farnell.com/edsyn/cr44/solder-paste-in-syringe/dp/876768?Ntt=876768. We're pretty excited about getting this thing started!
Another thing you need for surface mounting is PCB. You can't use breadboard or strip board, you must design a Printed Circuit Board and get it made. So we used Cadsoft's Eagle software - http://www.cadsoftusa.com/
The library for this LED couldn't be found on the internet, so we made our own, and it is attached to this blog post. Feel free to use it, but as I haven't used it yet... I can't promise it's quality!
The first board is this:
And the corresponding schematic:
Actually I think I might change it to only have 1 LED per board... 3x3W LEDs seems a bit excessive! The board and the LED should be here by next Tuesday.
