I've spent quite a bit of time tinkering with the robot over the past several months since the growing season started.  I've made a few adjustments to the design of the bearings and gears which I've outlined below:

- The spacing of the gears on the right side of the robot was slightly off (due to the fact that I didn't use CAD software to map out the placement of them :)).  Instead of making a whole new titanium or aluminum plate, I rotated the mounting of the bearings just enough so that I could move the mounting holes closer together so the gears were mating properly.

- The fairloc hub gears that I originally used on the motor shafts ended up  not working in the long run.  This is the gear that doesn't have a set screw, but uses a screw to tighten the hub around the shaft.  They held up for several weeks, but then began to slip.  To fix this, I drilled and tapped a hole for a set screw in the hub of each of the gears and am using that configuration now (1 set screw in each hub which goes into the flat portion of the motor shaft).

- The bearing mechanism I put together also failed under stress - the bearing that is facing in towards the blade starts to get loose and then allows too much play in the axle and the gears start to slip.  I came up with two fixes for this issue.  The first was to use a .25" aluminum piece with a hole drilled out so that the bearing fit through.  Having this piece of aluminum in place seems to help support the bearing facing towards the blade so that it doesn't move around.  The second fix which I have in place on one of the wheel axles is to take the bearing apart from the flange mount and sandwich the bearing inbetween two aluminum pieces.  I drilled the aluminum pieces part of the way through so that the bearing fit into each piece and then drilled a smaller hole completely through so that the axle would come through.  This seems to be a good design for the wheel axles since they have the hardest stress put on them.

After these adjustments and changes, I've not had to do any fixes in the past 3 weeks or so and the robot is working well - returning to its base on a regular basis aside from the few times it gets hung up on my kids' swingset. . . . .