A FEW MODIFICATIONS

In order to remedy the crashing problem with our tracks, we decided to make the front tracks skinnier, so that they could fit within the rear tracks. That way, all the clearance issues were resolved, since the tracks were no longer directly inline, as shown in Figure 7.

Figure 7. A thinner profile on the front tracks allows them to ride inside the rear tracks.

In playing with this new configuration, we found that by making the pivot axis shared between the drive axles, we could get the maximum flexing clearance. Unfortunately, this brought with it another design challenge: the left and right sides needed the ability to run forward or backward independently to allow the robot to turn. This meant that the tracks couldn’t just share the same axle going through both sides, which would have been the most straightforward way to solve the mechanical problem. Also, the front and rear axles had to be independent so that the robot could raise or lower the track without having to run the drive motors, and the center area needed to remain clear so that the track could swing through any angle. A robust mounting system using multiple pillow blocks was installed to join the two tracks without interfering with the drive system, as shown in Figure 8.

Figure 8. Multiple pillow blocks were installed at the common joint.

This joint allowed the tracks full range of movement (see Figures 9-12) and solved the crashing problem. With the crashing difficulty resolved, we moved on to gearing the motor for lifting the front track.

Figures 9. – 12. The new joint allowed the tracks full range of movement and solved the crashing problem.

The immediate solution would have been to use the largest gear in the additional gear kit. Unfortunately, this huge 84-tooth gear had too large of a diameter, and would have dramatically reduced our ground clearance. Adequate ground clearance was essential in this area, since the central pivot joint (and whatever gear is attached to it) almost touches the debris pile during a climbing sequence. In order to get enough clearance, we opted for the 60-tooth gear on the front track. This was driven by a 36-tooth gear on the rear track to get the correct spacing (pitch diameter) between the gears, as shown in Figure 13. Two motors were used to drive a common shaft, which effectively increased the available horsepower. We were careful to ensure that the polarity of one of the motors was reversed in the programmable mixing on the radio before doing a full power test. Since the motors were facing each other and turning the same shaft, if both of them had the same polarity, they would fight each other and possibly cause damage to themselves or the rest of the system.

Continued
<<Back | 1 | 2 | 3 | Next>>

return to the sample articles list