Servo - 201306

making a powerful flipper and just try to create a flipping mechanism that could fire three times without any human intervention.

Another reason that Reclipso was unable to really toss an opponent was the very limited gear ratio between the mass in the flywheel and the opponent. The hook and strap implementation of the trigger meant that the rear bar of the flywheel attempted to rotate at the same speed as the flywheel itself.

This meant that the flywheel’s momentum was being transferred to an opponent that weighed ten times as much without any reduction in between. In fact, because the flipper was a four bar linkage, the effective gear ratio was worse than 1:1.

The final result was an inefficient momentum transfer and very little actual flipping.

Now that I had identified the problems with Reclipso, it was time to solve them. The weapon speed controller was simple — all I had to do was find one with a user programmable low voltage cutoff and fit it into the robot. There were many to choose from, and I eventually settled on one that could handle up to 40 amps.

Unfortunately, the speed controller cutoff was the only problem that could be solved simply by replacing a single component. The other problems all required a complete redesign of the weapon assembly.

The new design (Figure 1)

FIGURE 1. Completed assembly with thread.

to slide the clutch downward until it lodged between the flywheel and the coil drum. This was done while the flywheel was spinning at full speed which caused the coil drum to spin rapidly, as well. I used Kevlar thread to link the coil drum and the coil plates that drive the rear bar of the flipper.

Every rotation of the coil drum reeled in more of the thread and pulled the arm through its stroke. The coil plates at the back of the robot were eight times larger than the coil drum shaft, providing an 8:1 gear reduction to make more efficient use of the momentum in the flywheel.

Once the flipper arm reached the end of its stroke, the thread went tight and everything stopped rotating. The clutch wheel was then pulled back and upward by a pair of springs, so it disengaged from the flywheel and coil drum.

Once the clutch was disengaged, the entire assembly could rotate back to its original position so it was ready to fire again.

There were a lot more moving parts involved in making this design work than there were in the simple steel hook design, but the potential for improved flipping was definitely there.

In Figure 2, you can see what the entire assembly looked like with the weapon extended. The flipper arm had not yet been bent to its final form for this picture, but you can see the four bar linkage including the rear hinge pin from Figure 1 (right next to my hand).