Battlebots
As part of the Texas Robotics Department at UT, I participated on a team for combat robotics. We competed at Battlebots: Metal Mayhem at SXSW. My role on this team consisted of mainly hardware. We had 5 weeks to design, fabricate, and build a 15 lb battlebot.
I designed multiple components of the bot and integrated the assembly to ensure all the pieces fit seamlessly. In addition, I performed some calculations to assist with assembly of the final bot.
Electronics and Specifications
We first started by making detailed notes about all the specifications and restrictions needed to build the bot. The bot weight restriction was 15 lbs, and to make a more sturdy and structurally sound, we decided to keep our bot fairly compact.
We researched multiple drive and weapon motors, as well as the ESCs, and batteries. This entailed talking to vendors and ensuring the electronics we had met the regulations. A lot of our research also consisted of talking to previous battlebot competitiors on their recommendations
Side Panels
One of the main parts I designed was the side panel. These panels were a key structural component of our bot as multiple other pieces, such as the bottom plates and the wheel guards, mounted to these. Based on the weight distribution we had, we decided to choose AR-500 steel for this piece. This was done to provide more rigidity and toughness against any hits The side panel contained all of our components and would be taking a lot of impact as most bots tend to hit the sides of the chassis. The piece was designed as a 1/4" panel with mounting holes on the bottom for the bottom plate, and the back for the back panel and wheel guards. In addition, there was a mounting pattern for the drive motors to secure to. This entailed makings sure we matched the sizing and the pattern with the specs on the motor data sheet. These were all designed as through holes. Another key design aspect is the pockets. To maintain structural integrity, but also cut weight, we cut out pockets in a triangle pattern to reduce some of the material. Lastly the front of the plated has a large hole for the axle of the weapon, and has two extensions coming out that serve as touch points to the ground during drive. These were included on both sides of the panel to let us drive the bot even in the case of being flipped over.
Initial Design
We started our design off with a very "dirty" CAD model. This included the overall footprint of the robot. Marked area for all the electronic components and a general design of the pieces that would fit together.
One key design choice we had to make was the type of weapon we wanted to use. Based on the limited timeline and past experience, we chose to doe a vertical spinner, or beater bar. This simplified our electronics and programming and enabled easier assembly.
Wheel Guards
Another part that I took the lead on was the wheel guards. The main purpose of these parts is to protect the wheels and take the majority of external impacts. We started with HDPE as our material, and upon recommendation from our mentor, we switched to UHMW as it had similar strength properties, but was a little less dense. The design of the guards were based off a few key requirements - give clearance for the wheels, have an arc to prevent grabbing from other weapons, and minimize weight. To accomplish this I designed the piece with multiple arcs, each being tangent to each other and the planes they aligned with. This created a smooth and flush assembly for the pieces. In addition, the wheel guards also matched the front of side panel with a semicircle shape and holing in the middle for the axle of the weapon. To make the pocketing, I kept the walls around .2 inches thick to maintain some rigidity, and added fillets to the end of the triangular sections to account for machinability.
Prototyping
Due to our wheel guards being manufactured late into our build timeline, we prototyped our own wheel guards to check fittings and make sure the pieces of the entire bot came together. We first 3D printed a piece to fit, then machined a block of UHMW and printed out the drawings as a stencil. Using that as a guide, we used a bandsaw to cut the rough shape out and employed a sanding belt to get the dimensions more accurate. The pocketing was done with multiple drilled holes as well as a Dremel to sand off an excess. The pocketing was not as critical to test the fits. Lastly, I used drills and endmills to make the through holes and counterbores respectively, and we were able to use this as a fit to test weight balance and to practice driving.
Bolt Torque Calculations
For assembly, we had multiple fasteners, or screws, that bolted into aluminum. This posed the potential problem of over torquing our bolts and cross threading. To prevent this, I used the material properties of the bolt and threaded material, as well as dimensions of the bolt to calculate the max torque needed to tighten the screw. I set up an excel sheet to do these calculations and went through each fastener to make sure our bot was assembled correctly.
Take Aways & Recommendations
One of the oversights on our end was a consequence of our post processing. Our side panels and bottom plate were powder coated to produce a more aesthetic appeal. However, this increased thickness ever so slightly and not allowing our assembly to fit. We were able to fix this problem by manually milling down our backplate to allow for a smoother fit.
One of the parts that we had to alter after fabrication was our wheel guards. The wheel guards were manufactured through UHMW CNC machining, but we did spend some time manually machining new holes for the mechanical hard stop as well as to accommodate some new hubs for our wheels. This problem mainly arose due to the timeline, and us not being able to iterate more design changes.
