Servo - July 2010

that might sneak in underneath (as shown in the right side of Figure 2, just before The Judge was launched by Ziggy). To avoid that, it is a good idea to move the center of mass of the hammerbot forward.

The right portion of Figure 2 shows that the tilting angle of the chassis is increased even more after the hit, due to the reaction impulse from the impact. The speeds after the impact and all the involved impact energies can be calculated from the very same equations used for spinners. Since the attacked robot is hammered against the arena floor, it usually does not move its center of mass, it only deforms due to the attack. This impact problem is similar to an offset bar spinner hitting a flexible but very heavy wall as shown in Figure 3.

The attacked robot would then have an infinite effective mass (not exactly infinite, but that of the Planet Earth!), while the

FIGURE 3. A spinner is basically a sideways HammerBot.

hammerbot’s effective mass would work like an offset spinner. The speed of the attacked robot after the hammering is, of course, zero. The hammerbot chassis gains vertical speed and may, in fact, spin backwards.

Note that if the back wheels of the hammerbot are still in contact with the ground immediately after the impact against the opponent, then a second impact will probably occur. With the back wheels gaining a downward speed after the initial impulse, they will press against the arena floor and receive a vertical reaction impulse. This back wheel impulse is good for the hammerbot, because it prevents its chassis from tilting backwards too much. The final linear and angular speeds of the hammerbot chassis can be calculated using the same equations from the second impact that happens when a robot is hit by a drumbot or vertical spinner. (These proofs are fully developed in the Tutorial.)

Summary

In this mere 1,000 words, I’ve managed to grossly simplify the treatment of this subject from the Tutorial. A longer article on ThwackBots — a close cousin to HammerBots — is in the offing, which should serve to provide a more thorough understanding of the mechanics of this interesting and scary weapons system. SV

BUILD REPORT: A Reintroducti n to Wedges

● by Thomas Kenney

In mid 2007, I began the construction of Gilbert — MH Robotics’ first antweight. The bot has gone through many revisions over the years, beginning as an inertia-labs kit with sheet metal bent over the top to form a wedge, and going on to become one of the flagships of our fleet of overpowered bricks sporting hinged wedges. The second revision of our hinged wedge design involved a titanium shaft supporting two to three blocks of UHMW or aluminum, to which was secured the wedge piece itself. This general design suffered from a few issues before it was applied to more of our bots; most of these