Servo - June 2008

being used so often now that it is hard to tell the difference between them.

The Sportsman Class

The Northeast Robot Club (NERC) realized that this progression towards spinners and wedges was driving the creativity out of the competition. They watched many builders get burnt out from the sport because they no longer had the time, energy, or money to rebuild after every competition. To counter these issues, the NERC created the 30 pound Sportsman class. The basic idea behind this new class is that no wedges are allowed and no spinners over 400 RPM, but an active weapon is required. The goal of the Sportsman class is to allow other designs to be effective again, and prevent complete destruction of robots in a match.

The first few competitions proved to be effective in its goals. A resurgence of hammers, flippers, actuated spikes, and even saw blades for wheels were seen. However, even with these designs, builders were stuck “building in the box.” The robots were gaining personality, but builders weren’t trying things that hadn’t been done before. It was really fun to see designs that hadn’t been done in 10 years, but the true potential of the Sportsman class had yet to be seen.

included flippers. This was for a very simple reason: Everyone was accustomed to building low to the ground boxes, perfect prey for a good flipper. To counter this, I reasoned that if a robot was higher up in the air than the flipper arm could reach, then it would be rendered completely ineffective. With this basic idea in mind, I set about designing a new robot to take advantage of this weakness.

The Birth of Herald

Throw it Out the Window

The elimination of wedges and uber-spinners now allowed builders to throw everything out the window they had previously known and try something new. I noticed that for the upcoming event there was a lack of entrants in the Sportsman class, so I decided to build one. The question was what would I build, and how would I make it unique and effective? Thus far, the most dominate design in the class

To begin, I named the new project Herald. First, I had to decide how I would make Herald tall. The most obvious method of raising the height of a robot is to use very large wheels. However, I found this impractical given my budget, weight, and time constraints. So, looking for alternate ideas I thought of the 60 pound robot, “Archetype,” built by Team Delta in 2002. It featured four “legs,” each of which contained a motor at the end with a wheel. I then took this concept and morphed it; instead of making the legs out of a stiff material such as aluminum, I decided to use UHMW — a type of polyethylene. For this application, it was perfect because it would give the robot a completely independent suspension that would be impossible to damage in the Sportsman class.

One issue with this design was that with the center of gravity so high, it might be prone to falling over. To counter this,

I designed each leg so that its height could manually be adjusted, meaning my total height could be adjusted.

With that part decided upon, I now needed a simple, easy, and fun weapon. I decided on a hammer. Then,

I realized that because the body of

the robot was so high up, I could do something that had never been done before — a hammer that swung 360 degrees. This meant I would have to add one interesting feature to the design. Herald would have to consist of two frame “pods” connected by a hollow, stationary shaft to allow wires to run from one pod to the other. The hammer would then swing around the shaft.

I was now ready to create a list of parts to build the robot out of. I decided to use four drill motor gearboxes and hobby motors for the drive. For my weapon motor,

I determined that an EV Warrior motor would be adequate, which is a discontinued surplus motor. In the electrical system, I decided to use a 14. 4 volt Nicad battery that I already had, along with an IFI Victor 883 speed controller to manage the hammer and an RS80D dual channel speed controller for the drive train. I decided to use the software package Solidworks to design the robot. The CAD model can be seen in Figure 1.

The Build Process

There were a few specific design problems that I had to address to ensure the robot would be a success. The first was that hammer mechanisms are subject to almost instantaneous stops. Some builders have had problems with attaching sprockets to the motor shaft so that they don’t shear off.