I'm going to kick off the team's website with a build report on Mandy Bulls, our scuttling little fairweight shufflebot that was quite the darling among builders and audience members at the Canadian National Championships (Kilobots XXXVII). This is the first one of these I've ever done, so expect it to be somewhat unorthodox as far as a build report goes.

I think it's a tradition for first-time builders and those new to the sport to have some sort of crazy, advanced plan for a machine that really doesn't have much of a chance of coming to fruition given their experience and skills (I have a lot of these as well, trust me). Mandy Bulls was something of a take on one of these. A walker was one of the first "wild" ideas I had when it came to doing a followup to Grater Good. I had already built one machine, a basic wedge, in the fairyweight class and was itching to try something a little more radical. I had no real goals in terms of combat performance, I just wanted to make something interesting to watch and look at.

The biggest inspiration for Mandy's design was Christian Carlburg's "Pretty Hate Machine", an eight-legged robot armed with sawblade arrays on either end of the robot. With offensive weaponry on both sides, it wouldn't have had to maneuver as much as its opponents to bring its weapons to bear. Mandy Bulls was conceived as both a miniature version, and as an update of sorts to this late-90's design (heck, I was even considering calling it "Mini Hate Machine"). But how to design a full legged walking mechanism when my only prior experience in frame building consists of bending a cheese grater in a vice?

Enter the Tamiya 71119 Stag Beetle kit. Using a simple cam system and already set up for (wired) manual control, it was an obvious choice as a platform on which to build a machine. I owned several Tamiya kits in my youth, and they sprung to mind when I considered how to build a walking mechanism. An order to Pololu nabbed me the chassis and drivetrain of what would become Mandy Bulls. I figured that if ten year old me couldn't break one of these puppies, it'd be up to the general stresses of moving around the arena.

With the kit built and in my hands, thoughts turned towards armament. As the kit already weight 158 grams without any of the necessary electrics for remote control, the weaponry would only be on par with normal fairyweights. My thoughts boiled down to two major concepts: A horizontal grabber system, using the already-included stag beetle jaws, and a small drum to be mounted on the front (with a second one on the rear, should the weight allow) as an updated take on Pretty Hate Machine's saw rack.

After deliberation with other roboteers and family members, I decided to go with the drum mechanism over the horizontal claws, feeling that while grabbing claws would undoubtedly look awesome and fit with the beetle theme, making it effective and durable was beyond my abilities and interest in what I considered a "secondary" project next to Sawful and an updated Grater Good.

Electrics were rather simple. To keep costs down, much of Mandy Bulls' electrics were pulled from the spares purchased for Sawful and The Grate Gatsby. Power is supplied by a pair of Lectorn Pro 3.7v-180mAh 45C Li-Poly packs wired in series. The 2S setup was chosen since it gave the best driving characteristics for the legs. 3S would likely have provided more oomph for the drum weapon, but I found that the legs would simply rattle and the machine would jump around when under full power rather than move forward. The leg motors are controlled via FingerTech Robotics TinyESCs, which have proven damn near bulletproof in my experience. They also provide the battery eliminator circuit for the HobbyKing T6RA Reciever. Although this somewhat large receiver was a bit of a weight investment for a robot that would only require three channels, I wanted to use the same part for commonality among all three of my machines in the event one blew. For future revisions of all three machines I'm looking at moving to a smaller receiver due to space concerns. Finally, the excellent FingerTech Robotics Mini Switch controls all power to the machine.

This un-armed platform provided plenty of good experience for driving a shuffler while me and my father worked on the weapon as well as other machines. Mandy Bulls is reasonably fast once it gets up to speed, but unlike wheeled robots it doesn't have much in the way of starting or stopping traction. As such, the whole robot feels far weightier in maneuvers than you'd expect from a 225 gram machine. Also stemming from the "shaking" movement of the robot, it can be unpredictable in a straight line. To counteract this, in my fights I drove Mandy Bulls at around half throttle, reserving the full power for charges and fast turns. This early prototype even had a garage-floor "battle" with Brian Cassin's Derpy Dozer after a day of working in his workshop on our various machines. Unfortunately, we didn't have enough time at Nationals for a grudge match between the two finished machines. You can see the first drive test of Mandy Bulls here.

With the robot walking around well, next it was time to work on the weapon. My father has a more substantial workshop than I myself have access to, and the amount of work he devoted to getting Mandy battle ready cannot be understated. Given the limited weight we would have, we decided that wood was the ideal material to build the drum weapon out of. We did consider thick plastics, but felt that wood would hold a thread better for attaching teeth. The drum would attach using the mounting holes originally intended to hold the kit's grabbing jaws. The drum and mount was designed with the teeth having a bit more ground clearance than most drum robots have, in order to prevent the weapon from catching on the ground during high-speed maneuvers.

Mandy Bulls' drum is powered by an EFlite Park 180 brushless motor wired to a Turnigy MultiStar 10A brushless ESC provided by Brian Cassin two days before the tournament after the original ESC failed to work. It was chosen due to its low weight and small profile. To isolate the motor from potential drum impacts, the weapon was designed to be belt-driven rather than direct drive. For the belts, we simply took some Solarbotics Traction Bands and cut them in two.

Unfortunately, in testing of the drum we found that the belt had a habit of attempting to "climb" out of the groove towards the center of the drum. While it would never get far enough to catch on teeth, we found that it would prevent the drum from spinning up again, should it come to a dead stop. This is partly due to the somewhat low voltage Mandy runs at, coupled with the generally low power of the motor itself. It also had a pronounced lack of bite when tested against a pizza box. You can see the finalized Mandy Bulls testing its weapon in this video.

This, coupled with the potential of facing powerful horizontal spinners, led to us constructing a second attachment for Mandy Bulls, the one which it wound up using in all of its fights at Nationals: a hinged plow intended to ward spinners away from the vulnerable legs. An unintended side effect of the mounting solution for the drum meant that Mandy Bulls was a great candidate for modular weaponry. Initially, much of the scoop was made of wood, with only the lower plow section being aluminum sheet. However with a fair amount of extra weight being available, we upgraded the size of plow to the one we used at Nationals.

We kept the plow attachment something of a secret in the leadup to Nationals. All of our progess shots showed off the drum attachment. In our eyes, revealing that the robot had an anti-spinner setup might lead to other teams using their own anti-wedge setups in battle with it. In the end, the point turned out to be rather moot, seeing as we never ran Mandy in combat with the drum, so everyone already knew exactly what Mandy's capabilities were after its first fight.

Overall, Mandy Bulls was a fun experiment. The crowd loved it, the other builders got enough of a kick out of it to give it the "Most Innovative" award at the end of the competition, and I loved driving it. Although I'd initially planned on retiring it following the event (since I expected it to go home in pieces the second it met a spinner), given the great reaction to it I'll likely come back to the design in the future, and hopefully make it a more competitive machine.