Background:

Having gained experience with our lightweight combat robot Bad Buzzard, we decided to build a heavyweight named Condor.
 

Cutting the Weapon Disk

Weapon Test (sans teeth)

S7 Tool Steel Teeth

Design Principles: (learned from Bad Buzzard)

Journal:

July, 2002- We have been collecting heavyweight parts for a while and now are taking Condor the first step beyond the pile of parts stage.

The first part we selected from our pile is a General Electric jet engine starter motor. This thing develops Etek-like power on only 24 volts and has a set of bearings hefty enough to support a weapon directly. On the downside, it weighs 45 pounds and draws over 400 amps when starting up.

Next parts were a Dalton torque limiter machined to fit the motor shaft, a 24 inch disk of 6061 T651 aluminum machined to fit the Dalton hub and a pair of S7 tool steel blades cut to bolt on the disk. The first test was run with the motor bolted to a plywood test stand, jumper cabled to 2 car batteries and no teeth on the disk. We clocked the tip speed at 347 MPH - that's about mach 0.46! When the teeth get back from heat treating, there's serious damage in store for anything that gets in the way of this weapon.

August, 2002- We got the teeth back from the heat treater and bolted them up to the weapon disk.

After reviewing our projected current drain figures, Steve Hill at Hilltop Batteries said to start with 5 BattlePacks for the weapon alone. Add 2 or 3 more BattlePacks for the drive system and that's about $1000 before buying extra chargers. Being an economically challenged bird, Condor may have to wait a while for a proper set of batteries.

Layout of Motors and Wheels

Drive Pod Schematic

The planned drive system consists of 2 mirror image drive pods. Each drive pod has 2 of Bad Buzzard's weapon motors driving 2 8"x2" Colson wheels via #40 chain. Drive motors are offset toward the rear of the robot to clear the much larger weapon motor. Gear reduction is 4.5 to 1. We are still debating on whether to use one Victor ESC for each motor or a Thor for each pair of motors.

September, 2002- Assembled both drive pods and propped the weapon up to get a better picture of the final configuration. For scale, the 4 small motors are each 7 inches long and 3 inches in diameter. Before starting to build the actual frame, we plan to construct a plywood prototype of the frame to test the drive pods and weapon under power.

Assembled Drive Pods with Weapon

October, 2002- To minimize the need for spares, we decided to have as many interchangeable parts as possible between Condor and Bad Buzzard. This meant ordering four more Victor ESCs, two Astroflight chargers and a Futaba PCM receiver. Couldn't get sixteen of the 2AH BattlePacks any more, so we bought nine 3.6AH NiCad BattlePacks for approximately the same power and price. We saved over $100 by modifying a surplus 24 volt power supply to produce 13.8 volts to drive the 2 new chargers.

Plywood Prototype

The first powered tests showed a tendency for the weapon disk to kick upward on forward acceleration and to dig into the arena floor during reverse acceleration. The plywood prototype should let us correct this problem before cutting our first pieces of titanium.

November, 2002-

Registered for Robocide at Orlando in January. The rules are a little fuzzy, but they seem to have a new restriction on spinners. It looks like they count the motor armature towards the 20% weight limit. Not being able to get a clear ruling nor willing to take chances, we bored a pattern of holes into the disk to get the combined weight under 44 pounds. There's not much we can do about being over their diameter and RPM limits, so we submitted a request for spinner pre-approval. Thanks to material from our sponsor, we assembled the titanium frame and got rid of the plywood. It's starting to look more like a robot and less like a pile of parts now.

Titanium Frame

December, 2002- As soon as we completed the assembly, it was time to take the whole thing apart again for weight reductions. We drilled rubber out of the wheels, removed any aluminum that didn't have a bolt through it or serve a structural purpose and replaced the steel sprockets with nylon ones. The process eliminated over 30 pounds of unneeded material.

To comply with the new RFL rule set, we had to add lights to indicate when power is on. Our initial thought was to glue a battery powered strobe to our Team Delta power link so it would be visible when plugged into the robot and not when in the tool box. Though simple to implement, we weren't sure that idea met the intent of the rule since someone else's link could still power up our robot. The next idea came from our county fair where vendors were selling disco earrings for $5 a pair. Each earring had 2 LEDs, a flasher circuit, 3 watch batteries and a magnetic mount. Replacing the batteries with a 3K resistor made it easy to wire into our 24V electric system.

We cut and fit titanium armor panels to each side and made a pair of titanium wings. Adding a Lexan dust cover and sponsor's stickers completed the assembly with 2 weeks to spare before Condor's first competition.

Power Indicator

Completed Assembly

Test Drive

January, 2003- At Robocide in Orlando, Condor lost its first match to Phrisbee by judges decision after a full 3 minutes. The armor got a little chewed up around the edges and the roller bearing in the torque limiter failed, but no internal parts were damaged and we retained full mobility throughout the fight. We quickly tacked the ragged edges of the armor back together and reassembled the torque limiter with a steel bushing to replace the failed bearing. We won our second match against Four Letter Word by knockout. In our third match, we took a good sized chunk out of Hexadecimator before Condor got flipped over and counted out.

Our plans to participate in the heavyweight rumble got unexpectedly cancelled. While we were out to lunch, one tray of Condor's BattlePacks spontaneously ignited and a number of other competitors had to quickly open an unfamiliar robot to extinguish the fire. Using foam to separate adjacent battery packs was a bad idea. Next time we'll pick a material that neither melts nor burns.

Questions or suggestions?

Email me at Steve@Heard.com

Links:
BattleBots Competition rules
Team Coolrobots - excellent links.
Team Delta - sells robot parts.
Team Nightmare - Big website. Check out the DB of competitors under the "links" section.
Bad Buzzard - our first combat robot.
Robocide - first event of 2003.
Titanium Joe - Our sponsor. Titanium sheet, plate, tube, bar stock and bolts.