The main chassis needs to hold the large motors together, and ideally, also support the outer ends of wheel axles. While wheels can be securely pegged onto motors, not only through a central axle but also with friction pegs, supplemental rigidity comes from supporting the other end of axles with some sort of frame. This ensures a better control of the trajectory of the robot, especially when it starts to be loaded with cargo or has added weight from various attachments.
Of course, the chassis is also the platform onto which the rest of the attachments are fixed, as well as the control brick.
We decided to make extensive use of the 5×7 rectangular bricks, because they have a large surface, they are light, and they can hold other beams or more 5×7 together, in their inner free space of 3×5. We have also used the H-type 5×11 rectangular bricks — they have the same inner free space but extend with two holes on each side. Below we can see a side and a bottom view of our chassis:
These are the main elements of the core of our chassis
- The two large motors are held together with a 5×11 rectangular frame beam (part number 64178) “onto which” they are fixed — the motors have two 3-hole-beams attached under them, at one hole distance, so each motor goes on top of one of the short sides of this frame.
- More 5×7 rectangular frame beams (part number 64179, also called “liftarm”) are “embracing” the main frame and the back of the motors, and two more 5×11 are set below them, to form the true bottom of the chassis
- We use a few more small frames to make everything fit tight.
- We add two more 5×7 vertically, “in front”, to have them go all the way “up”, on the other side. This can serve as a place to securely affix other beams or parts, by “squeezing” them in an exactly one-hole space, with three-hole pegs, between the front-of-motor-attached three-hole beam and the two 5×7 top parts.
This is how it all looks “in real life”, with the blue side plates to provide support for the wheel axles, small beams to attach them, and with a detail onto the back of the motors. Observe how the wheels are attached to the red rotating part of the large motors.
So one driving idea along all these design choices is to keep interlocking the frames, while allowing for space to tightly anchor something else, on top, to build attachments or other structures.