COMBAT ROBOTICS
Destroy or be Destroyed
WHY?
I've made combat robots for three years because I love to build. CR gives me an opportunity to put my designs up to the test of head-to-head competition, something I learned to love during my time in FIRST robotics. This has taught me how to engineer robust mechanical and electrical systems ... often times by learning the hard way.
MEET BLUR
Blur is my current independent combat robotics project. It was created to compete in the beetle weight class, which means it must weigh 3 lbs or less. Though brutal, this robot’s objective is to destroy its opponent without getting destroyed itself. It features a 4 wheel drive, CNC milled UHMW side plates, carbon fiber top and bottom panels, bent titanium front armor and an AR500 steel kinetic-undercutter weapon.
WATCH IT FIGHT
WHAT'S INSIDE?
The robot has three brushless DC motors, one for the left drive, one for the right drive, and one for the kinetic weapon. These three motors are powered by a 4s 850 mAh LiPo battery. The drive motors (2100kv) run through a 27:1 planetary gearbox reduction giving about 1151 RPM at 14.8V (nominal voltage of the 4s LiPo) which translates to a linear robot velocity of about 11.3 ft/s.
The higher powered 1000kv weapon motor goes through a total reduction of 1.49:1 after a gear and belt reduction and spins at a nominal speed of 10,711 RPM at the output shaft.
SIMULATION
When designing the weapon for Blur, I wanted to validate that the weapon could withstand a full force impact without significantly deforming. To test this I set up a dynamic event FEA simulation in Fusion which modeled the time steps immediately after impact between the weapon and another robot (in this case the shell of one of our other robots). The spinner was set to spin at max speed (~6k RPM) with about an inch of weapon engagement.
SPIN-UP DYNAMICS
Quick weapon spin up times (time to max RPM) as well as the maximum kinetic energy the spinner can store are both very important metrics for a kinetic weapon combat robot. More energy storage generally means more energy that can be transferred to your opponent.
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As seen in the graph to the right, Blur’s 0.6 lb steel weapon spins up to max speed (10,711 RPM) in about a second with a kinetic energy of 440 J.
ELECTRONICS
Blur uses typical R/C hardware to convert transmitter controls into robot motion. A RadioMaster R84 receiver receives radio signals from a controller/transmitter and sends those signals out to each of the robot’s speed controllers. A battery eliminator circuit (BEC) is used to regulate the battery’s 14.8V down to 5V to power the receiver.
CNC MACHINING
I used a Carvera desktop CNC to machine the aluminum weapon shaft bearing block and the UHMW plastic sidewalls for Blur. To actually generate these operations, I imported the models into Fusion and used Fusion CAM tools to create machine paths. Since the aluminum bearing block had features on both the top and bottom of the part it required two different toolpath operations.
ADAPTIVE DESIGN
Blur's weapon was originally designed for a 30 lb robot. When first designing the weapon, I created an adaptive design that takes the ideal weight of the weapon disk as a parameter and then scales the geometry appropriately so that the disk is not only the proper weight, but also geometrically balanced exactly at the center of rotation. Keeping the disk balanced eliminates gyroscopic forces when the disk is spun up to extreme speeds. When adapting this design down to the 3lb scale all I had to do was feed in the new weight parameter and my design was done!
