Fight, Robots, Fight! Built at Hive

The original ALF 120lb combat robot, 2005.

Many folks surely remember the days of fighting robots on TV: Battlebots, Robot Wars, Robotica, etc. And while its televised days are behind it, the sport is kept alive by groups of builders and competitors across the country. The Northeast Robotics Club (NERC) is just such a group, and one that I have been a member of since I first saw robots destroy and get destroyed on TV.

In the years since, I’ve traveled up and down the East Coast competing with robots of my own. But this past weekend, our own city of Philadelphia hosted NERC’s annual Franklin Cup, held in conjunction with the Franklin Institute. For this event I decided to continue the lineage of a long-standing family of NERC bots: ALF!

Now, this is the first robot I’ve built since I’ve moved to Philadelphia. My center-city apartment is about the size of a large phone booth and lacking any machine tools, so it’s obviously not a good workspace. The Hive, on the other hand, with its storage space, large work areas, and 24hr availability of tools and resources, was the perfect place to build. It may sound like a shameless plug, but the story of ALF would be incomplete without it.

From the start, this robot was to be a testbed for a some new ideas. Firstly, I decided to make the robot an exercise in ease of construction (Design for Manufacture or DFM is what they call it in the real world). Using off-the-shelf mechanical components from McMaster-Carr and SDP/SI helped with this immensely. Standardized hardware meant that the whole machine could be stripped bare using a hex key set and a socket wrench.

Most of 30lb ALF’s innards.

For the weapon, I chose to build a quick firing spring-loaded hammer – something a little on the exotic side as far as combat robots go. I had never built anything like it, and I’ve always found something innately appealing in the cams, rollers, and linkages involved in such mechanisms. The rotary cocking/release interface was very fun to build and watch in action, providing about 180 hammer blows per minute.

One-piece Lexan top armor, complete with neccesarily obnoxious paint job.

Additionally, I wanted the layout of the robot to be very open and easy to repair. While this was helpful at the competition, the layout made for a lot of unused space inside the bot. Using a one-piece shell of formed Lexan for armor meant that every component was immediately accessible with the removal of four bolts.

In not much time at all, ALF was ready to fight! I had a simple, straightforward robot driving around with a working hammer mechanism – all of this a few days before the event and weighing in at a cool 29lb. With that I considered the build a success! I was off to the Franklin Institute to see how it would fare in the arena…

This just goes to show you that after years of building and competing, anything can happen once the match starts. Unfortunately, the motor powering the hammer mechanism stalled within the first few seconds of the fight, causing the last stage of the gearbox to fail catastrophically. That is to say, there were stripped gear teeth everywhere when I opened it up. So that was it for the hammer, unfortunately.

ALF patched up alright!

As for the top armor, I was surprised to see Lexan crack so easily as I’ve always known it to have excellent impact resistance. I tend to think that the lack of serious structural members supporting the shell allowed it to flex just enough to the point of fracture. ALF’s underside, which took a good deal of hits as well, was the same material  but bolted directly to the frame’s steel base.

But even though basically every major component inside of ALF (drive motors, batteries, controllers) took multiple direct hammer hits, somehow, the drive system worked as well as ever. For the remainder of the competition, ALF was weaponless, but there was nothing to do but fight on.

Without its hammer, ALF was a sitting duck in all its other matches (the videos of which I will leave to the reader to find on their own…). One highlight was ALF’s fight with the pneumatic flipper and defending champion, Upheaval:

ALF at the end of the competition.

At the end of the day, ALF was beaten, battered, and relied on much more duct tape than the original design called for. Ultimately though, I accomplished nearly everything I wanted to with this robot – apart from beating other robots. I can’t say I didn’t gain a whole bunch of knowledge though. And as with every project, I’m just cutting down the number of mistakes I have to make in the future.

Watch this space as I begin work on rebuilding my flagship robot, Such and Such: a walking, clamping, elaborate beast of a machine.

Big thanks to NERC, the Franklin Institute, and Hive 76.

Interested in fighting robots?
NERC – Official website, look out for competitions.
Robot Combat – Everything you need to know to get building.


4 Replies to “Fight, Robots, Fight! Built at Hive”

  1. Well, the motor is rated for something like 1400 in-lbs of torque at stall, which is a little ridiculous. The manufacturer even says that the gearbox isn’t robust enough to withstand that torque (which is really just poor form in my opinion). The rotary cocking mechanism probably got jammed when it had to quickly change direction when ALF got flipped, and the gearbox probably kicked. The motor itself was fine and ran perfectly well when disconnected from the gearbox during post-mortem.

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