Seattle Mindstorms™ and Robotic Techies : ~48/CrateContraption/2004/Robothon


Organizations / United States / SMART / David Schilling / CrateContraption / 2004 / Robothon

The Crate Contraption - Robothon 2004

Robothon is an annual event for robots of all sorts, shapes and sizes. Most of the robots there are handsomely crafted machines, usually with circuit boards showing. Sometimes someone will bring a Lego robot, though. And occasionally these Lego robots show the metal & PCB robots a thing or two!

This year SMART decided to put on a crate contraption at Robothon, to show some more interesting things that you can do with Lego robots. The display was a huge success. The crowds were always pretty deep around our table. The judges also loved the display, giving the entire thing an award for “Coolest Robot”. (They couldn’t guess ahead of time that the “coolest robot” would actually be a cooperating collection of robots!)

The Crate Contraption was a simple one, basically just three robots plus a motorized lifter. The layout we used was rather tight. It would have been nice to have some more space, but we were restricted by the setup used by Robothon. One benefit of such a small layout was that you could see everything at once, and take it all in. Basically the dump truck moved balls around, and the forklift moved crates.

Here are some Overview videos showing the whole layout in action. It’s not necessary to download them all to get an idea of what was happening.

Overview 1 - 0:45 (size 12Mb)

Overview 2 - 0:39 (size 10Mb)

Overview 3 - 0:30 (size 8Mb)

Overview 4 - 1:14 (size 20Mb)

Overview 5 - 1:09 (size 18Mb)

Overview 6 - 0:27 (size 8Mb)

Overview 7 - 1:19 (size 21Mb)

(If you need to download the DivX codec, <http://www.divx.com> will have it - download and install to see the movies in Media Player.) Divx

Robot Descriptions and Videos

Dump Truck:

The dump truck is a robot that can track lines in both directions. This allows it to back up after collecting or dropping off balls, just like a real dump truck would. In the Robothon layout, the dump truck drove around the outside of the layout, making a ‘normal’ turn after getting its load of balls from the hopper of the propeller lift, and a three point turn after dropping off its balls. This is a tricky maneuver to do when line tracking; what made it possible is that there are two light sensors for tracking the line - one in front for when going forwards, and one in back when going backwards. The one not being used is simply ignored. That let the three point turn work because when you change directions, the other light sensor would be over an otherwise disconnected portion of the line. See the layout or the videos to see how this worked.

Along with the forklift, the dump truck used an interesting scripting system. The program contained instructions on how to track lines, how to switch from tracking one side of the line to the other, and how to dump, etc. But it wasn’t until the layout was finalized that these pieces were put together by ‘writing’ a script using the Lego remote control. This allows great flexibility, and avoids constantly downloading new versions of the program every time a minor change is made in how the lines are placed on the layout. (You can read more about the scripting system in this post.)

The dump truck was designed by Gus Jansson. Dump Truck Video - 2:09 (size 35Mb)

Forklift:

The forklift is a redesigned version of the one used at last year’s NWBrickCon. It has the ability to pick up a crate and carry it, and put it down again. In addition, it can also lift the crate high up, and dump it out! Like the dump truck, it can go forwards and backwards. It also uses the scripting system.

The forklift would take a crate from the end of a line of crates, dump its contents onto the propeller lift, and push the now-empty crate into the front of the line. The crates were refilled in this line by the chain lift.

The forklift was designed by Gus Jansson. Forklift Video - 2:22 (size 38Mb)

Propeller Lift:

The propeller lift was designed as a reliable way to lift balls to a hopper that would fill the dump truck in the layout. The way the balls are elevated is by using the three-pronged liftarm that came in the Gigamesh Spybotics set. Dozens of these rotate in sync, meshing so that each one lifts the ball just a little bit. Balls are dropped into a hopper at the top of the mechanism. A light sensor waits to see when the dump truck arrives, and once it’s there, stops the lift, opens the hopper to drop a load of balls, and then closes the hopper and starts the lift again. The reason the lift is stopped is so that balls don’t continue falling into the hopper when the doors are trying to close, as this might jam them partially open.

The propeller lift was designed by David Schilling. Propeller Lift Video 1:07 (size 18Mb)

Chain Lift:

The chain lift was designed as a reliable high-volume ball lifting mechanism. The dump truck would drop its load of balls into the lift, where they would be distributed to a line of waiting crates. The chain is just a bunch of technic pieces linked together, and is powered by a constantly running motor driving some medium wheels over which the chain runs. Originally it was going to sense the presence of the dump truck, and only turn on when it was there, but this proved to be problematic.

The chain lift was designed by David Schilling. Chain Lift Video -0:28 (size 8Mb)

As is usual with this complex a system of robots, they didn’t function properly all the time. Here are some of the bloopers (1:26; size 23Mb) that were caught on video. One interesting thing to notice is the last one, filmed during “integration” shortly before the show, has the forklift doing an extra push of the crates to get them snuggly in line in front of the chain lift mechanism. This was cool to watch, but took too much additional time to do, so it was left out of the final script.

Thanks to Gus and David who built the robots and put on this version of the crate contraption! Thanks also to Mark, Doug and Patrick who provided other robots that we showed at Robothon.

Primary content in this document is © David Schilling. All other text, images, or trademarks in this document are the intellectual property of their respective owners.