Sometimes I build robots that attempt to solve real world challenges. Other times, robots are built based on random ideas. This robot is a case of solving a LEGO challenge – specifically, with their Technic tracks/treads #575518. At no fault of theirs, these plastic tracks are slippery on many surfaces. Great for carpets, flat areas, dirt (if you dare) – and great for turning as well. However, when you try to climb with them, they are as slick as ice.
If you Google them, you will find some great ideas on making these treads more ‘sticky’. Some have used 1/2 Technic pins (which fit nicely into the supplied holes), others have used elastics wrapped around them – all great ideas that work fine. I attacked the challenge from a different angle. The result is DG – or Dual Grip (yes, the name is somewhat plain). DG went through numerous revisions as I worked out kinks related to weight, stability, traction, sensors, flex etc. At the bottom I have included some pictures on previous versions of DG – some changes significant, others subtle.
The idea was to have a treaded robot that could navigate varying terrain, turn quickly and of course, climb. Based on my experience with my other robots using the same tracks (eg UNV and DynaTrax), I found that they were not very good when it came to inclines. I figured that the LEGO rubber wheels have great traction on most surfaces, so why not slap a set of them along with the treads. However, this posed another challenge. I did not want both wheel systems in contact with the ground at all times as this would make turning tougher and be redundant.
What better way to test a colour sensor then to create a brick sorting robot! After getting my hands on a HiTechnic colour sensor, I first took a stab at creating a robot that could navigate a room and detect colour. There was only one problem, it could not really do what I was hoping for. I was nieve in thinking that I could build this robot and it could detect colours from a distance. After reading the fine print on the provided documentation, I quickly realized that the colour sensor is only capable of reading colours at very close range (~ 1 cm). My bad. Of course, you could still build a robot that uses the ultrasonic or other sensor to get it close to objects, then read the colour… but that’s for another time.
BrickSorter uses this colour sensor to detect the colour of bricks and sort them into a variety of cups. The program is quite simple, gravity and studless beams allow for each brick to slide down the track on its own. when a brick is next, the colour sensor takes a reading (more on this later), the sort motor turns the sort rails to the correct cup, the sort rail motor changes its angle depending if the cup is close or far and finally the kicker motor kicks the brick in motion.
After a lot of fooling around with the cup placement (which seemed to be the hardest part of this project!), I managed to get the sorting pretty much bang on. Of course, the video shows some goofs, but that is mostly due to the small sized cups (its all I had!)… Anyway, I found the sensor to be accurate most of the time, but ambient light still influenced the readings at times and caused for the odd random missorting of a brick. I had to shoot the video about 10 times to get cup placement and sorting goofs worked out.