There is a common phrase used within the combat robotics community which is "design for your construction". Simply put, there is no point designing an amazing design that you physically cannot build with the tools you have at your disposal. Since I only relatively recently moved into a house, I had limited tools of my own beyond typical hand tools. I knew that the primary resources I would have available would be a short time using my friend's CNC router (Matt of RAD Robotics), and online laser cutting/2D CNC routing services such as SendCutSend and CNCMadness. With that in mind, I knew my design would have to be based around a few CNC routed UHMW parts, and the remainder of the frame would have to be 2D carbon fiber/metal profiles that slot and tab together. I've had a lot of success with the slot and tab design concept previously with Translationally Inconsistent.

To the upper left you can see the initial frame design. It consisted of 2 UHMW weapon rails, 2 UHMW drive rails, Carbon fiber base and top plates, and a titanium wedge. Due to time constraints (I didn't procrastinate at all... /s) I actually went to Matt's house to get all the UHMW parts cut out before I had completed the rest of the design. Everything in the design was notionally *there*, just not fully refined. I was fairly certain the drive rails and weapon rails wouldn't need to change at that point... I was wrong. Turns out I had forgotten to set the correct material density to the titanium wedge and the AR500 disc, so the design was subsequently about 6 ounces overweight. Whoops. That's what I get for waiting to long to start a design.

Since I already had the weapon and drive rails cut. I desperately tried to save that weight in other parts of the frame, but to no avail. I realized I would have to ditch the original frame rails, make them out of something lighter, and make the chassis shorter. Cue Version 2 of the frame! As shown to the left, The drive rails were changed to carbon fiber and the overall length of the bot was reduced by about 0.75". In addition to the carbon fiber drive rails, I had to add in a few 3D printed parts to properly space out some driveline components, to allow for the dual belt setup outlined below. With the robot's design now coming in underweight, I quickly sent off the DXF files for the carbon fiber components to CNCMadness, and the titanium components to SendCutSend. I highly recommend both companies, as they are reasonably priced and I had my parts in hand within a week.

One of the keys facets to a successful 4WD vertical spinner is a powerful drive train. I opted to go with the following components:

• 2X Kitbots 1000 RPM Gearboxes

• 2X DYS BE1806 2300 KV Motors

• 2X Lumenier Razor Pro F3 BLHeli_32 ESCs

• 2X GNB 3S 550 mAh Batteries in series

• 2X Fingertech S3M 15T Dual Timing Pulley's

• 4X Fingertech S3MTiming Belt

• 4X Custom Polyurethane Wheels on 3D printed hubs

I've seen the BE1806 motors used with Kitbots gearboxes before (AKA 5 Minute Brushless Motors), and they proved to be very powerful and fast. While the drive system does run on 6S, I limit the drive speed to 60% of what it is what it is capable of, as I know the gearboxes would not like to be used at the full 6S speed.

All of these components are mounted onto a carbon fiber drive rail. The front wheels are placed slightly in from the real wheels in order to help them tuck behind the front wedge. Each wheel will be powered via a timing belt which runs to the centrally mounted gearbox. Each wheel mounts on an aluminum block which is then mounted on 2 slots in the drive rail. This will allow each drive wheel's belt to be tightened independently.

While a large portion of the weight for this robot goes towards both the frame and the drive system, there is a (relatively) small AR500 vertical disc. This disc mounts on a machined pulley which is connected to the weapon motor via a belt. The following components are used:

• Custom 3/8" AR500 blade cut by SendCutSend

• Custom Machined pulley with Fingertech Needle Roller Bearings pressed inside

• BrotherHobby Avenger 2806.5 1700 KV Motor

• Holybro Tekko32 F3 Metal ESC

• Custom Motor Mount with McMaster Bearing 7804K136

• Fingertech S3M Timing Belt

• 3D Printed Motor Pulley

Since this weapon blade assembly isn't particularly heavy (~225g rotating mass), I knew it would have to have an aggressive bite to ensure that a high amount of energy is transferred to the opponent. The weapon tooth profile was carefully designed to make sure the back side of the tooth does not push the opponent away from the blade once the front side of the tooth gets worn down slightly. The blade assembly is mounted to the weapon rails with a 3/8" Shoulder Bolt and a Distorted Thread Locknut.

The motor mount assembly is designed to be replaced as a complete unit, which can be quickly replaced between fights if necessary. Since the weapon blade pulley is toothless, the entire assembly needs to have some ability to tension the blade. Normally, I would put slots in the baseplate of the robot and slide the motor mount back and forth. Since Boop the Snoot has such low ground clearance, I have to use countersunk screws on the underside, which would make a slotted design less than ideal. For Boop the Snoot, I decided to slot the motor mount itself, and then have a second aluminum plate the mounting screws would go into the clamp the motor mount in place.

With all the systems put together, we get the final design! I designed a weapon motor fairing to protect any miscellaneous shrapnel falling into the motor, as well as the sloped sides to the wedge that will hopefully deflect any hits that aren't taken head on. Both the motor fairing and the sloped sides are designed to be printed out of Polymaker Polymax PLA. Normally I would go for a nylon filament for this type of application. But at the second Huntsville even I saw someone print their entire antweight's frame out of this material, and it held up very well. Polymaker claims that this PLA is 9X tougher than regular PLA. Given that I was having some issues getting good layer adhesion out of my nylon 3D prints, I decided to try the Polymax PLA.

Before hardware or wiring, the design came out to ~2.7 lbs. Having a 10% margin for a wiring loom and the hardware should be sufficient to make the final 3 lb weight.