Friday, 5 December 2008

End-project. PART II

Date: 05 12 2008
Duration of activity: 2 hours
Group members participating: all group members

1. The Goal

The goal of this lab session is to finish building the carriage that is able to go back/forth (that is x-axis movement) and some part on top of that carriage that is able to go left/right (that is y-axis movement).

2. The Plan

  • Finish building the carriage.

  • Try to build a part that can move left/right with regards to the carriage.

  • Mount motors and test how well platforms are able to move.

3. The Results

3.1. Movement

The biggest challenge of this lab session was to keep up on building. So far, we had the ``lower'' platform which is responsible of forwards/backwards movement handling, and on top of this, an ``upper'' platform (the ``carriage'') is put (the platform that will be going forwards or backwards). This ``upper'' platform is responsible of leftwards/rightwards movement handling.

To make it easier to imagine all the directions of movement, this little schema introduces the platforms in play. Most importantly, it all corresponds to movement in X-Y-Z coordinate system.

If the construction succeeds, in the final version we will be able to move in a three-dimensional space.

3.2. Platforms together

The idea that enables the carriage to be able to move at all is rather simple: we take two plastic axes (or, actually, more than that, but divided into two parts) and mount them with ``spindles'' (which are actually more appropriately called ``screw conveyors'', but ``spindle'' is the word we're settling on) that are able to take a LEGO-gear-grabbing linear drive from the beginning of the axis to the very end. In order to accomplish that, the weight of the load wouldn't be on the gear itself, but rather on small flat wheels that were mounted for that purpose.

Here you can see those platforms (the lower one and the carriage) on top of each other:

3.3. The carriage

From the basic point of view, all that was left was to build a top sliding part, mounted on top of ``upper'' platform (the carriage), that is able to go leftwards/rightwards. This part has to be able to move an attached head up and down.

So the top of the carriage itself, has an axis with mounted spindles. The idea again is similar to before: To make a sliding part (the leftwards/rightwards movement) mounted with a gear grips into the spindle. This is the aforementioned ``upper'' part (the carriage) taken apart:

3.4. The part for Z-movement

The next important part to consider was the actual construction doing up/down movements. Lifting obviously has to be handled by a motor, and the fact that a motor has to be directly connected is a bit of a burden (which to no small extent was because of the limited space available in this advanced place). The problem of mounting the motor in a fashion that linearizes its movements can be solved by different solutions. Our used approach was a creative one: Instead of more obvious ``gear to gear'' approach, we decided to go with ``rubber-wheel to smooth-plastic-surface'' approach. This has the advantage of being simple and---in some sense---continuous in its movement, but the drawback is that it requires a lot of tension to work reliably and therefore the motor has to give a lot of power in order to make any movement at all. This issue will be discussed later.

This is how the construction (of the part that is able to slide left/right on the carriage) looks like:

Now, the part that is responsible for handling up/down movement has to be connected somehow, put on top of ``upper'' part (the carriage). For that, a sliding construction is made. Here it can be seen, mounted on the platform and by itself:

3.5. Final outcome

Due to the final construction, we have the main lower platform, the carriage on top of that, and the sliding part on top of the carriage itself. The carriage is able to move back and forth as a motor is connected to the main axis (which moves both sides' axes and thus enables the movement). The sliding part on the carriage is not able to move yet, but it will. The plan is to mount a motor to drive the only axis on the carriage, and a third motor will be connected to the sliding part itself (to enable movements up/down).

And so the overall construction when all the parts are put together looks like this:

With regards to programming, some basic motor controlling was done. With a motor mounted on the ``lower'' main platform, forwards/backwards movement was tested in different speeds. We were satisfied with the performance as the sliding happens smoothly enough. There still are problems to be solved: Sometimes a ``tooth'' or ``groove'' of a spindle is skipped, which is a very undesired property. The solution for this will come is postponed to later in the process.

4. Conclusion

This lab sessions was a productive one. We have a main ``lower'' platform on which a carriage is able to move (this corresponds to an x-axis movement). The carriage itself is mounted with a sliding part that will be able to move from side to side (this corresponds to an y-axis movement). The sliding part is made in a way so that a part of it is able to be lifted up/down (this corresponds to a Z-axis movement). What is more, X-axis movement was tested with simple software programs.

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