What do you guys recommend for a project that requires collecting scattered legos from the floor and placing them in a bin?
The floor could be carpeted and have other toys scattered around.
Dyson cordless vacuum
So I should clarify that these are Duplo pieces that are significantly larger than the typical lego pieces.
They are designed for pre-schoolers.
In that case, a shop vac!
http://www.homedepot.com/p/RIDGID-6-Gal-Wet-Dry-Vac-WD0670/202198493
You need Arduino involvement in this somehow? Like a pincer arm that can reach out & grab a piece once detected? Or a dustpan/mini conveyer belt with a brush in front to move pieces onto the belt?
I'm thinking one mobile bot to push pieces around on the floor.
Another static assembly to lift them into the bucket via pincer, belt, etc.
The multi-brick configurations may need to be broken down.
Yes, a small shopvac is always an option but indulge me anyway.
How's this for a start?
change the plow shape to keep bricks from sliding off the sides.
or the sparkfun kit
both also have tons of parts to roll your own.
These are great! Thanks!
slmnhq:
I'm thinking one mobile bot to push pieces around on the floor.
Fork lift truck??
The difficulty there might be getting the forks under the brick.
Another static assembly to lift them into the bucket via pincer, belt, etc.
If your static assembly had a thin flat platform the bot could just push the brick on to it. Raise the platform vertically and tip it once it is above the level of the bucket. I'm imagining something like
- Two umbrella shaped runners (handles at the top) for the platform or
- A protrusion on the back of a hinged platform that comes into contact with a static part at the top of a straight lift so that it tips the platform towards the bucket.
We're only talking hollow plastic "bricks" about 1"x1"x2" when separated, so getting forks under one would not be difficult.
I have (now grown) children so know exactly the physical properties of Lego and Duplo bricks. I even know the pain of standing on a lego brick in bare feet. 
The problem is that the bricks are light and, on a fairly smooth surface, will slide away rather than onto the forks.
Heavier bricks wouldn't be so much of a problem.
It might be possible to tip the bricks on their side with the forks placed high on the brick and then use the hollow base to pick them up. Duplo bricks, being larger, would be easier for this method.
Walking around barefoot is another way to get rid of them - step on one, toss it out!
Maybe a suction hose with a screen on the end can pick pieces up?
GoForSmoke:
Maybe a suction hose with a screen on the end can pick pieces up?
This was my first thought as well.
Put a section of heavy screen (the kind with 1cm x 1cm holes) behind a vacuum hose (a shop-vac would work well). Dust and small particles will get sucked through the screen into the machine, while bricks would stick to the screen. Then you just need a beam-break sensor or something in front of the screen to detect the bricks. A simple T fitting with a flap would work for gravity-dependent brick extraction. When the vacuum is on, the flap gets sucked shut, and seals. When a brick is detected, kill the vacuum motor, flap opens, brick falls out the bottom of the T (and into a bucket or something).
You wouldn't even have to stop the motor, just open a hole up hose of the end.
I would use smaller diameter plastic tubing and a less than heavy duty (noise) motor but still such a thing would need a cord and wall plug unless you really, really like batteries.
Make the 'roomba' look and act like a robot elephant or octopus (8 creepy hoses). Put the container as the body.
Hard part is only getting the Legos. Color recognition might help there.