Robin Newman’s Lego© Mindstorms© Page A beginner’s journey 7

Colour Sorter 4

Believe it or not I have just made a fourth coloursorter! This one again just uses parts from the NXT2 8547 set

The second model was tricky to setup as the bins were quite close together and there was only limited movement of the delivery arm. I explored therefore the possibility of using a vehicular base to the delivery chute, so that the robot could then move back and forward between the bins which were to receive the balls. That was the idea, but in practice it proved to be tricky for a variety of reasons. First I looked at using the body structure from the second robot, but with the bottom delivery chute modified to be similar to the first version. I built a tracked vehicle base and managed to mount the body structure on this. However, it was not very satisfactory as far as the position of the centre of gravity was concerned, and I found that the robot veered to one side as a result. I persevered with this version and added some ballast in the form of AA cells, and eventually got it going. You can see this version on my youtube site rbn1tube here. although I have not produced building instructions for it.

The other area I spent a lot of time exploring was to try and use the ultrasonic sensor to detect the position of the bins as the model moved along. This proved to be quite difficult and I could not get reliable results. The logic for the program also became quite complex, as you had to detect and count how many bins you had passed to reach the correct destination. Eventually I abandoned this in favour of a dead reckoning system which was much simpler. I think the ultrasonic method could work, but might need the model to use a guided rail system (lego train track?) to define its path more closely, and this would use additional parts outside the 8547 set.

I redesigned the support for the NXT brick to give a more stable system with the CofG in a more central position. All went well until I realised that I had inadvertently used three extra parts above the allocation in the 8547 set, so it was back to the drawing board until I eventually managed the design using parts just from the 8547 set. The resulting model uses a program very similar to the first colour sorter, although the gate motor is now on port C rather than A so there is a new MyBlock for the closegate routine. Also, as there is no sensor to detect the "parked" position, the section to return to base when no further objects are detected is a little more involved.

Full building instructions are in the navigation section or can be downloaded here. The program can be viewed on the program picture page, or downloaded here. (Building instructions updated 13/12/2010 to add four missing steps!)

Once again I am happy to receive comments on robin dot newman at gmail dot com