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:

The Skid Steer Drive

The Skid Steer drive is truly a classic drive system. Usually incorporating treads or 6 wheels, good examples of skid-steer drives in real life include excavators, tanks, and other utility construction equipment.

A common variation of the differential drive (more on that later), the skid-steer has:

-better grip on rough floors/terrains
-more torque and power, where friction uses up some of the motors power
-easily maneuverable, however programming a skid steer to go straight is a little tricky.

The one I built above uses two motors powered by the same RCX. The chassis is divided into three parts (seen here). Two different mounts for each independent tread, and a central mount for the RCX and motors.

The wider base provides stability, which is important for slow moving treads, and a low center of gravity keeps accidents like tipping, and slipping from occurring.

An example of a clutch gear.

Another important component of a skid-steer (and pretty much all drives) is to incorporate elements to keep your motor from jamming. If a tread or a wheel gets caught, but the motor keeps trying to apply power, there's a dangerous chance of a lot of broken parts. My design incorporates a clutch gear which provides a certain domain of resistance before the clutch keeps the motor spinning with no damage (regardless of the status of the wheels).

Finally, shifting gears, and increasing the ratio provides massive increases in power, sacrificing speed in the process. Because my motor is directly linked to the 8t, which turns the 24t, my gear ratio ends up like:

                                                                               8t : 24t = 1:3

Which basically means that my wheels are turning at 3x the power the motor is outputting.

Skid-steer drives are fun to build, and even more satisfying to watch in action, and I definitely recommend experimenting with a few of your own designs to get started. If you have any alternate designs or suggestions shoot me an email: ashwin.johri@gmail.com