Servo - October 2009

no more. The other driver was gracious enough not to get in a free hit. I made sure to properly attach both gearboxes to their mounts before the second match. In UFO’s previous match, their shell had been dented inward to the point that it was irreparable and completely prevented the weapon spin-up. The team opted to replace their shell with a large steel bar angled at the tips. Shaka was able to drive fine

this time, but due to the huge twisting force, UFO flipped over upon spin-up.

There are several things I plan to improve on in Shaka when I get the chance. First, I’m going to decrease the width of the robot at least 1.5” by removing the Dewalt pillow blocks and supporting the shaft by pressing bushings into the UHMW side. I also plan to remove the weapon bearing blocks and

replace them with a pair of bushings pressed into the weapon support rails. I’ve already replaced the battery with one that has a more adequate discharge rate.

Overall, I’m happy with the little combat performance that this robot has had, and will be taking it along with the rest of the MH robotics fleet to the upcoming Franklin Institute event to find any other bugs that need to be worked out. SV

MANUFACTURING:

RioBotz COMB T

TUTORIAL SUMMARIZED:

Materials – Part 2

● Original Text by Professor Marco Antonio Meggiolaro; Summarized by Kevin M. Berry

Professor Marco Antonio Meggiolaro, of the Pontifical Catholic University of Rio de Janeiro, Brazil, recently translated his popular book, the RioBotz Combot Tutorial, into English. Last month, SERVO summarized the first part of Chapter 3 — “Materials” — focusing on commonly used metals in combat bot building. This month, we switch focus to non-metals.

Marco’s book is available free for download at www.riobotz.com. br/en/ tutorial.html, and for hard copy purchases (at no profit to Marco), at www.lulu.com/content/7150541. All information here is provided courtesy of Professor Meggiolaro and RioBotz. Let’s get started!

The main non-metals that need to be mentioned in

combat robot design are:

Polycarbonate

This popular plastic — commonly known as Lexan (trademarked by SABIC Innovative Plastics, Inc.) — is a polymeric thermoplastic (which softens and melts when heated, instead of burning) that is transparent to light waves and radio-control signals. It has high impact toughness, and it is very light, with a density of 1.2. When used in combat robot armor, it absorbs a lot of energy as it is

deformed during an impact. In spite of that, fewer and fewer combat robots have been using this material, because of its disadvantages: it has very low Young modulus (E = 2. 2 GPa — about 1% of the stiffness of steels — making the robot structure very flexible even for high thicknesses), it cracks easily (the cracks usually appear starting from the holes, and they propagate without absorbing much of the impact energy), and it is cut easily (becoming vulnerable to sawbots).