mini-artic-loader

h1. DriveTrain

The drivetrain for this machine is the most complicated part - everything else should be straight-forward lego engineering, fabrication, and machining.  It will be composed of two rear axles coupled to a transfer case, which gets its power from the hydraulic motor.  There are some considerations when choosing these components that we will discuss in turn.

h2. Axles

Through some research into this topic we have determined that there are some unexpected forces experienced by the axles in an articulating steering design.  That motion is modeled in %{background:red;}source:TODO% and traced out in light blue below.  The two triangles represent the two halves of the chassis and the two vertical lines represent the axles.  Notice the side loads exerted on the the ends of the axles, ie: the wheel hubs and axle flanges (not shown), shown by the blue arcs at the ends of the blue line. 

!{padding-left:10%;width:15%}https://projects.absolutepowerandcontrol.com/attachments/download/37/artic.axel.paths.png!

These forces look to be approaching the wheel face at about 45 degrees, which should cause some wheel rotation (if the wheels are free to spin) *and* side loading of the hub and flange.  This is born out by watching some "video of the GatorS machine":https://youtu.be/cB65qZEx3YM?t=164 in action.  Use 1/4 speed and pay attention to the flexing of the left rear tire as it counter-rotates forward.  It is clearly being twisted sideways between the friction force on the ground and the pushing action of the axle.  Experience from the "MBN Forum":http://machinebuildersnetwork.com/ubbthreads.php?ubb=showflat&Number=3282#Post3282 also indicates that there are significant torquing loads placed on the axles when articulating at a stand-still.

We believe another aspect that plays into this is how the hydraulic motor behaves when in 'neutral'.  If it creates a hard braking action through the drive train, that can lead to much more stress on these components when articulating at a stand-still. The combination of that scenario coupled with a locking differential would certainly over-strain the system where the torque loads are highest (ie: big wheels/tires with aggressive tread bolted to drive axles).  When the wheels are trying to drive the axles during counter-rotation while articulating, and the drive train does not allowing the axles to spin with the wheel, either the tire has to flex enough to absorb that motion, slip and scrub sideways on the ground, or break something in the drivetrain. 

These factors inform our choice of axles for this project, which will be GM 3/4 ton 14-bolt 'corporate' "full floaters":https://lugnut4x4.com/axles/corporate-14-bolt-axle-explained/ with open differentials and preferably the slip-on brake drums.  To meet our size parameters for the machine, these axles will need to be shortened to obtain the ~5 ft wide stance.  That means that if any drive axle breaks, we will have to shorten a new one if the old one cannot be repaired (which is likely).  However, this choice of axle gives us the following advantages to offset that one (major) liability:

# They are very common and so shouldn't be too expensive

# They are very strong - they have been used in 1 and 3/4 ton vehicles for many decades

# The full floating variant means that:

## a drive axle can be removed without removing the wheel, which makes repair easier

## if an axle does break it is much less likely to tear up bearings and seals because of the bolt-in design

# Slip-on brake drums allow for easier maintenance of those parts

## the other option is the stud-mounted drums, which have the drums pinned in place by the wheel studs.  These are harder to replace, though if the drums are in good shape it is unlikely they will see enough wear in this machine to ever need replacing.

We believe these aspects of these axles make it well worth the effort to shorten them for our purposes, plus they are the recommended choice of experienced builders on "MBN":http://machinebuildersnetwork.com/ubbthreads.php?ubb=showflat&Number=3282#Post3282.

h2. Transfer Case

h3. Drive Shafts