Firebug is a 12lb combat robot built for Norwalk Havoc Combat League (NHRL). It is a heavily armored pyro-bot that utilizes cast foam and a large can of butane to defeat its opponents.
Unlike most robots in this weight bracket, Firebug utilizes very little metal for its construction. Firebug is made primarily of 3 materials: UHMW plastic frame with cast foam and TPU 3D printed armor.
The UHMW frame is milled out on a small CNC Machine. The top and bottom panels are 0.25" thick while the 4 frame members are 1" thick.
The grey wedges in the front of Firebug are actually made out of cast foam. They are very soft, picture a couch cushion. They are made by pouring a liquid foam mix into a 3D printed mold. A TPU 3D printed retainer is used to attach the foam to the frame.
Weapon - Fire
The flamethrower is made up of 4 components: the activator, canister, feeder/nozzle, and igniter. The activator presses the canister, which opens the valve at the end of the canister. This allows the butane to flow through the tubing, up to the nozzle which is then lit by the igniter.
A TPU 3D printed mount and a 25kg Servo were utilized to activate the butane in Firebug. The servo is massively overkill for the amount of pressure required to depress the can but it was what I had on hand at the time.
Firebug runs close to the maximum allottable fuel that is allowed at NHRL. The current fuel of choice is Ultra Blue Butane. These are ready to go, off the shelf, cannisters of butane that are inserted into Firebug.
There is no feeder line in these cans and they are placed into Firebug horizontally. Once the can gets to roughly half capacity, it stops spraying liquid butane and starts to release gaseous butane instead. This transition causes a major drop in flame. One of the interesting effects of this is that the pressure of the can quickly drops to almost zero relative pressure, but since butane boils at room temperature it will continuous regenerate pressure, up to about 16 psi.
The valve end of the canister is contained by a TPU 3D printed part. The feeder allows the nozzle of the canister to be depressed, which then feeds the liquid butane into a 1/4" tube. The tube runs along the top panel of the robot up to the nozzle.
Ignition is powered by a Pulse Generator and a RC Switch. This made a nice large continuous spark, but seemed to damage the receiver it was plugged into. During the fight with Demogorgan the ignition system was offline before the fight even started, the 3rd channel of the receiver had given out and was no longer functional after 3 previous matches.
Locomotion is handled by two oversized Flipsky H5045 out runner motors. A standard gearbox was avoided by using such large and slow motors. The motor choice helps by reducing failure points, cost, and weight. The oversized drive motors are paired to two cast foam wheels poured around TPU hubs.
Drive Motors and Controllers
Controlling the H5045's is a pair of 4.12 VESC's that each have their own independent switch and1300MaH 6S Turnigy Graphen Battery. This split system was able to keep Firebug driving even after Smeezus tore off part of Firebug's side armor, ejecting one of the batteries and a receiver.
Firebug's wheel comprise of a TPU Hub / Retainer, and a cast foam tire. The molds are printed in ABS and consist of two parts. The hub slots into the top section of the mold, once combined the top section of the mold is set atop of the bottom section. A 2-part foam mix is then poured into the mold. Roughly 12hours later the mold is removed from the wheel utilizing a pneumatic nozzle.
After the flashing and overcast is removed from the wheels, a coating of Rubber Cement is added. The purpose of this coat is to create a better bond with the next coat, the traction layer. The traction layer is 2coats of Liquid Latex . This helps the wheel get a bit more grip to the floor.
Two nylon bushing are pushed into the hub. White Lithium Grease is applied to the bushings and a shoulder bolt is used as a dead-shaft to connect the wheel to Firebug.