Featured Parts: Axles

Lego axles, in addition to connecting pegs, will be a crucial element of any robot you choose to construct. Whether used for structural support, or connecting two wheels along a single axis, lego axle beams have hundreds of important applications.

Axles come in about a dozen different sizes, and they geometry (unsurprisingly) meshes well with other lego blocks. It's not easy to determine spacing rules for beams, because most of the time spacial distances are dictated by the axle itself!

In my post about differential drives, we detailed how you can connect wheels on two separate axles; however keeping them aligned in the same order, spinning independently. You can also use wheels on the same axle, so that it will spin by itself along with the attached wheels, however this construct has many limitations when it comes to application in advanced topics.

As mentioned above, the geometrical construction of axles coincide nicely with corresponding lego parts. Here's an example of a gear run through an axle, all held in place by a supporting beam block. I thought it illustrated the different relationships between the parts nicely:

Differential Drives

By far the most common drive system for Lego robots, the differential drive is probably the easiest to make. Utilizing two parallel drive wheels on either side of the robot, they can be powered separately, or use a single motor as well.

The diagram to the right shows what a basic differential drive looks like. Bevel gears placed in the central gear housing allow the axles to turn independently, enabling the robot to turn in place, and maneuver pretty easily.

The following chart is adapted from "Building Robots with Lego Mindstorms" by the Ferrari Brothers and displays the different behaviors of  a robot in accordance to its wheels (powered by the differential drive).

Using different combinations of speed and direction, the robot has the ability to cover any amount of space, and turns at any angle. All this in addition to being very easy to implement. 

I assembled an example of a standard drive, showing how you can use the bevel gears inside the housing to attach the axles, and connecting it to an RCX is as easy as sliding two beams through it. 

As always, I encourage you to send me your designs, and contact me with any questions/comments/concerns. Happy building!