The Mindstorms LEGO Grabber. Delivery and Recycling Routes. Colored Line Follower V1

January 22, 2022

Today we challenged the kids to start working on a more advanced challenge: Build and program an autonomous delivery robot; but before that – we got a real treat from Coach Will!

Coach Will worked separately on his own Lego project over the past few weeks building an External Tank and Solid Rocket Boosters for the Space Shuttle Orbiter. He saved the a part of the project for the team. The kids added the final LEGO plates onto the Space Shuttle External Tank. 

We also learned an interesting snippet of information: The first two shuttle flights had the External Tank painted white to protect against UV light while still on earth, but color was later skipped in favor of saving a few valuable hundred pounds of weight.

Next we went continued with our FLL Explore CARGO project. In the last session, we decided to build an autonomous robot to move containers around: (1) A robot to move containers back and forth between Residential Distribution Center and Warehouse, and (2) A robot to move containers back and forth between a Recycling Drop off and a Recycling Center. Our initial idea looked like this:

From the Mindstorms NXT 2.0 Discovery Book, we wanted to give the ‘Snatcher’/ Grabber model a try and modify it to a line follower. Leon built it following the plan in the week prior to our session and we tried it out today: 

Brandon testing the Grabber
with the prototype box container

Wesley pushing the Grabber to its limits
with a couple of other objects.

As we mapped the outline of our board, we faced two challenges: (1) there is not enough space for two robots; with that we have to run a single robot for both routes, and (2) While the Grabber is incredibly cool (it grabs and lifts with only one motor!), it takes up too much space and lacks accuracy. The kids modified the grabber arm to a simple lift arm and built a container for the boxes. Below, Wesley is inspecting the partially finished version of the new lifting mechanism, and Bernd traversing the route to seek input from the kids. 

Colored Line Follower

Next challenge for the team is to design the Line Follower. We wanted to build two routes and use a color-sensor line follower for a single robot to go either the Delivery Route, or the Recycling Route. NXT 2.0 and EV3 can detect 6 colors, so we came up with the following design:


The game plan is as follows:

We noticed this is quite a build- and a programming challenge; but we can help the kids to break it down into simple steps. The black line is easy. The colored line are a challenge. We think the following:

Goal: Follow yellow

A. If White turn towards yellow

B. If Black turn towards yellow

C. If Green or Red or Blue, turn towards white and follow white.

D. If following White and we find Yellow, stop following White and start following Yellow again.

The robot knows whether it is driving towards the distribution center or away from it, so it should know which way to turn if it sees white or black while following.

Finally - for stopping at the end of each line. There are no colors left we can use to constitute a drop off/ pickup point. Leon suggested early on already to have a touch sensor bumper incorporated. So this would be our mechanism at the end of each line to let the robot know its time to drop off or pick up.