Structural Support with LegosStructural Support with Legos
Weight is a significant factor in the design of structural support. The batteries provide a significant load for the lego system. Not only will the car need to pull all this weight, but also must prevent itself from falling apart simply from the load. Therefore, construction of a strong weight bearing structures is essential to the completion of the project.
The frame around the batteries can best be supported by using bricks turned vertically and attached to horizontal bricks with the black cylindrical connectors.(1) You may run into trouble with the magic lego dimension, but this is the strongest way to attach legos to each other. To test the frame, drop it (without the batteries in it). If it breaks, then you need to start over. This technique should also be kept in mind if you are having trouble with compenents pulling apart anywhere inside the vehicle.
You will find that working with legos can be a real hassle. Legos only come in a few shapes and size. This makes construction difficult when you need a piece a certain size, but none of the given sizes will fit. So you must keep in mind the Magic Lego Dimension.(2)
This tells you the ratio of the heights of the two different sized lego pieces. Three of the thin lego pieces equals the height of the tall pieces. However, the width of the pieces is not the same as the height. This is a problem when trying to line up holes properly. The height of a brick on it's end is 6/5 the height of the horizontal brick. So creative stacking techniques must be used to make the legos match properly.
When constructing the car, you may find that certain pieces in the lower structure of the car may need to be replaced, repaired or modified. To do so may require the removal of many pieces just to reach below. Thus, to enhance repairability, modular structures are suggested. This means that individual units are built in such a way that they can be removed in one piece and separately.
For example, rather than entirely dismantling the gear box when trying to repair the frame beneath it, the gear box can be made to snap off the frame in one piece. Also, this method helps prevent dismantling of parts that cannot be reproduced (ie. you forgot how it went together).
The motor and servo can be cause problems in the structure of a lego car if they are carelessly connected inside the vehicle. The spinning motor expecially can be troublesome if not securely fastened. This may appear to be a daunting task since legos cannot be counted on to provide a strong bond between parts, but certain procedures can make the structure reliable in spite of the disruptive motor force.
Most importantly, any gear train beginning at the motor must interface properly with the next gear. Since these motor are not lego-ized, they won't automatically snap into place. Should the gear from the motor be too close to the adjacent gear, the motor will either spin off directly, or cause the motor to bind because of the added friction. If the gears are too far apart, the teeth get worn down rapidly. The gears should mesh in such a fashion that spinning the motor is easy and no slipping occurs. You'll will notice some play in properly constructed gear train, so don't let this disturb you too much.
But even with a proper gear interface, the motor has a tendency to spin off it's mount if not secured. This can be accomplished through numerous methods. A base which attaches to the motor along it's entire length works best, but is seldom sufficent. A top piece probably will be necessary as well. Attaching a the thin lego boards to the top and to an adjacent wall can serve as a good reinforcement. Also, attaching the expert builder blocks with the cylindrical connectors to a block above the motor and down below in the structure (see WEIGHT CONSIDERATIONS) makes very strong connections.
Servos have similar problems and can be treated in the same manner as the motors.
Shafts should not be used for structural support. Small weights can cause shafts to bend considerably, thus weakening the entire structure. In the case of small load, it may be used if necessary, but shafts should, in general, be reserved for spinning or mounting of spinning parts.
Particularly long, unsupported shafts will have a tendency to bend even under their own load. This may prevent the shafts from spinning properly. Support the shaft in short intervals to correct for bending.
