Servo - May 2009

Twin Tweaks ...

FIGURE 4. PROTOBOT.

FIGURE 5. PROTOBOT ELECTRONICS.

surgically removed the entire drive train to plunk it right down into the new Protobot.

The stock frame we used for Protobot was simple — just a long rectangle with two extra frame members running lengthwise. After installing the CIM motors and associated gears, we added four more caster wheels that we set slightly higher than the Colson wheels driven

by the motors. We thought this design would be effective at tackling uneven terrain and it had a bit more cool factor than a level drivetrain.

Building a frame and transplanting a drive train were easy enough, but the most daunting task was the installation of the electronics. Simple mechanical principles like how to build a strong frame and how to calculate gear ratios are accessible to even budding roboticists, but electronics can be another story. With hieroglyphic-like schematics and a host of enigmatic parts like speed controllers, breakers, and terminal blocks, hooking up the electronics for a robot can be downright intimidating.

Electronics have their own vocabulary and their own set of rules, and the learning curve can sometimes be prohibitive (especially in the six week time crunch of a FIRST build, some team members might be content to leave the circuitry to the experts). Thankfully, the folks at FIRST have provided ample documentation on the electronic components, and with two FIRST seasons under the belts of the Team 1079 veterans, we were ready to help the new guys unlock the mysteries of electronics.

The electronics in Modos were handily confined to a few mounting shelves, and transplanting the shelves onto the Protobot frame was relatively painless. The transfer was expedited by the fact that the stock frame came pre-drilled with a plethora of possible mounting points. The problem, however, was that Modos was markedly more complicated than the new bot we were trying to build.

The drivetrain was simply controlled by two Victor 884 ESCs, but the other mechanisms on Modos (the lifting arm, the grabbing fingers, etc.) were all controlled by Spike relays that were not necessary for Protobot.

Instead of completely eviscerating our electronics boards, we unhooked the wires to the newly unnecessary components. After excising the unnecessary wires, the overall goal of building Protobot was realized — new Team 1079 members got the chance to see that robots do not have to be that complicated to build.

The electronics in Protobot are fairly straightforward. The CIM motors connect to the Victors, which then run through some 40 amp breakers, a terminal block, and then onto the master switch that comes before the 12 volt Exide battery. The Victors also connect to the IFI controller, which connects to the radio. Taken as a whole, the Protobot circuit did not include a lot of components and the wiring consists of keeping track of the power and ground wires (with a few PWM cables thrown in there for good measure).

We built Protobot in literally a couple of days, and the low profile six wheeler was a great way to practice driving and to build confidence. Despite these positive qualities, Protobot has been neglected in Robot Central for years. One reason for that may have been the control system for Protobot.

There was nothing inherently wrong with the controls for Modos that were inherited by Protobot. The two joysticks gave the bot a truly high tech feel, the controls were