Date: 09 12 2008
Duration of activity: 4 hours
Group members participating: all group members
1. The Goal
The goal of this lab session is to put all our efforts into making the construction better.
2. The Plan
- Improve the sliding part (the one that moves on the carriage).
- Improve the carriage itself.
- Mount the NXT to be in a comfortable position with regards to the whole structure.
- Install emergency stop buttons.
3. The Results
3.1. Sliding part
The first thing that was done today was to improve the construction's part which is responsible for up/down movement handling. It was enhanced in a way so that now it is very easy to attach any kind of pointer or, in general, tool of any kind. In our case it is most likely to be a drawing pen. The wheel is the part that enables the movement itself with the help of the motor. The whole part is actually hanging onto the carriage, but it is clamped onto it tightly enough so it should be able to move left/right with no significant difficulty.
The aforementioned part looks like this:
3.2. The carriage
The second thing that was done---improving the upper platform in a way for it to be as compact as possible, so it would leave more space available for the X-Y coordinate system. The working area is not that big, so making the mounts as optimal as possible is an important issue. The pictures are showing the upper platform and its sliding area close-up:
3.3. The NXT
The third thing that was done was to attach the NXT brick onto the working area so it will be easier to work with it. This looks like seen below:
3.4. The touch sensors
The fourth thing that was done today: Attaching touch sensors. This was done for us to always be aware about what the limits of our coordinate system are. The lower platform (the main one for x-axis handling) got four touch sensors, the upper platform (the carriage for y-axis handling) got two sensors and the ``up/down'' platform presumably will get only one sensor, if at all. But that is enough, as all we need is to be sure that we touched the paper surface. Old kind RCX touch sensors are used for this purpose, since these can be connected in parallel (and we'll have plenty more input sensors than the NXT has input ports for, so this is necessary.)
With regards to programming, the X-Y movement controller was started. The initial idea is to give (x, y) coordinates as parameters to make the pointer move x tacho counts along the X-axis (forwards/backwards with regards to our working area) and symmetric for the y coordinate.
3.6. Final outcome
At the end of the work, it seemed that the part that is responsible for up/down movement would have to be redesigned. When attached to the ``upper'' platform (the carriage) it does not move correctly along the spindle axis, it gets stuck at some points. At the end of the day, the overall construction looks like this:
This lab session was all about the construction. Now we have the main platform, a quite final version of the carriage, and the improved sliding part. The sliding part is built in a way so that it is able to move left/right (y-axis movement handling) although with some spindle-related troubles that will be fixed in the future. Also, a part of the sliding part is able to perform up/down movements. Due to the overall construction, we mounted six touch sensors so far (four on the main platform and two on the carriage top) to act as emergency stops, so no platform would over-go the limits of the working area.