In early 2012 I built the first version of Nyx. After 2.5 years and over 30 fights across 6 events it was due for a major upgrade. The Instructable for the original Nyx can be found at https://www.instructables.com/id/30lb-Fighting-Robo...
With a win percentage over 70% Nyx had shown that many of the core elements worked quite well, but it had a few design elements that caused issues during events.
In addition to addressing those issues, a major goal of the design was to develop weapons that would operate in a more exciting fashion than the lifting spike.
If you're thinking about building this yourself, make sure to read through all sections of this instructable. If you have any questions, feel free to ask in the comments or via private message. I'll answer them as best I can.
Once the concept was settled on the design began on the base platform in parallel with the initial lifter and axe concepts. As the initial design approached completion the crusher module was added to the list of weapons and was added to the development process. Once the platform and all three modules were generally laid out a great deal of time was spent populating hardware and making finer adjustments to the systems to ensure that they would be within the 30lb weight limit.
The initial goal was a drive platform that weighs 18 pounds and a budget of 12 pounds per weapon module. By the completion of the design the drive platform weighed approximately 17 pounds and the heaviest module weighed approximately 12.5 pounds with gave a reasonable amount of margin for wires or calculation errors.
Design of the Platform
The core goals of the drive platform were to retain the speed and agility of the original Nyx, provide a compact, light platform for the weapons to mount to, and to at least meet the same level of durability of the original Nyx.
The design of the base heavily features Nutstrip and slot & tab design elements to create a rigid and easy to assemble body. The internal sides slot into the front and rear panels and are locked down with Nutstrip at each corner. The top and bottom armor are designed to bolt directly to more nutstrip running along the chassis side rails. The design utilizes wheel guards that strongly resemble those on the original Nyx. These wheel guards both protect the wheels and provide an outboard support for the axles to reduce the chances of bent shafts causing drive issues during an event.
The Dewalt Powerdrive Kits were brought directly over from the original Nyx, however for this design they are placed at opposing corners of the chassis and directly drive one wheel with the other wheel on the same side driven via roller chain. Compared to the original Nyx this setup will provide a higher top speed, lighter weight, and reduced complexity.
The initial wheel plan was to use a pair of BaneBots 2-7/8" x 0.8" wheels at each corner, however during the build process these wheels became difficult to find in the correct durometer and they were replaced with 3" Colson caster wheels and custom hubs.
No changes were made to the battery, as it had proven to be a good solution to powering Nyx for a full length match.
Over the course of the original Nyx competing it switched from Holmes Hobbies BR-XL ESCs to the Ragebridge ESC from e0designs.com. The new build integrates two Ragebridge ESCs, one for the drive system and the other to allow quick weapon integration with adjustable current limiting which allows the electrical system to be quickly and easily tuned to suit the weapon.
The new Nyx was designed to be fabricated using three sheets of material, 1/16" thick 6al4v Titanium for the top and bottom armor, 1/4" 7075 aluminum for the main structure of both the base and weapon modules, and 1/4" AR400 steel for the weapons. Limiting the design to these three pieces meant that there was less time loading material and setting up the waterjet cutting during fabrication. It also proved to be a good way to minimize scrap, as the individual components could be laid out in a way to minimize wasted space on the plates the components were cut from.
Design of the Lifter
For the lifter I selected a DeWut gearmotor from e0designs.com. The DeWut is a Dewalt drill motor in a custom mount with a custom output shaft that makes it well suited to robot combat. The DeWut is used in low gear with two stages of 3:1 reduction added to combine for a total reduction of 460.8:1. This combined with the current limiting on the Ragebridge being set to 50A means it would theoretically be able to lift 75lbs at the tip of the 23" fork arm. This was designed to greatly exceed the 30lb weight limit of the class because in addition to reducing the strain on the gearbox and motor, it also ensures that if the opponents center of mass is further from the axle than the tip of the arm it will at least be capable of lifting its weight. An additional design element meant to address the high loads on the lifter itself was the addition of 3 1/4" thick aluminum plates to each half of the lifter arm. The arm and all three plates are keyed to better distribute the forces incurred during a lift or sudden jolt to the arm.
With this module there is also an additional set of outriggers added. These outriggers help the robot lift an opponent without tipping. Without them, if the combined center of gravity of both robots was ahead of the front wheels they would fall forward. These outriggers move that point several inches in front of the main chassis of the robot, allowing it to lift most opponents with no stability issues.
Design of the Axe
With the axe the design started as a very simple idea: Build an electric axe with an A28-150 for the weapon motor. The A28-150 regularly sees use as the weapon motor for 30-60lb spinners and as the drive motor for robots weighing as much as 220lbs. An element that's often overlooked in electric axe weapons is that you have to dump as much energy into the axe arm as possible in 180 degrees or less. This means even with a fairly powerful weapon motor you'll likely need to add substantial gearing to maximize the energy output. The ideal situation would be to have the motor reach peak RPM as it contacts the opponent, however calculating the system to that level would take a great deal of effort, so I settled on the "good enough" option of an 18:1 ratio, which with the intended hammer size put the motor up over 4000rpm by the expected point of impact.
The question that follows that is how do you keep the motor from exploding due to sudden shock loading? There's no one right answer, however the approach I took was to integrate a torque limiting clutch into the hammer arm itself. The torque clutch is rated for 60ft-lbs of torque and with the planned 140A current limit and gearing providing approximately 66ft-lbs of torque at the shaft, it makes for a great fit. Now, instead of coming to a jarring halt, the motor is able to decelerate over a relatively large period of time.
The geartrain for the axe uses the same modified gears that the lifter uses for the initial 9:1 reduction, however for the axe there is an additional 2:1 reduction stage done via roller chain. Using chain reduction allowed me to keep the initial two stages of gearing lower in the assembly, lowering the overall system center of gravity.
The axe itself uses heavy triangulation of the weight reduction areas to minimize strength loss from the removed material. The main impact tip is designed to provide a balance between piercing and blunt force. While an extremely sharp point would be better at penetrating armor, it would also dull much more quickly than the style of blade used. This shape is fairly good for piercing, but has enough material at the tip that even against more durable materials it's not prone to noticeable deformation. The more traditional axe shaped head is primarily to move more mass out to the edge of the weapon but it is also a capable chopping weapon and should it be better suited to an opponent it can be rotated toward the front by removing the drive axle and flipping the torque clutch.
Design of the Crusher
The crusher uses a pair of Gimson Robotics GLA750-S linear actuators to power the crushing spike. Each actuator is capable of delivering 500 pounds of force and can extend at 2in/s. With the linkage ratios and a current limit on the Ragebridge that puts the motors at the maximum rated power (23A, 500lbf) the force at the tip of the spike is estimated at 670 pounds. To deal with this force, hardened steel axles are used both at the back of the actuators and for the weapon axle. The rear mount points on the actuators and the ends of the output shaft have been drilled out to 3/8" and 1/4" respectively to increase the shear resistance of the shafts they connect to.
The whole weapon portion of the module is designed to float. The benefit of this arrangement is that if the bottom of the opposing robot is higher than the lowered position of the arm it will automatically lift into the opponent, providing a firm grip on the opponent and keeping all four drive wheels on the ground.
The top of the mount portion of the weapon module is designed to limit the total vertical travel of the arm to ensure that it doesn't potentially get flipped over in combat. The shape of the mount also functions as a roll cage for the actuators, protecting them from damage should the robot be flipped. This is the only attachment that isn't capable of self-righting, and as such it is not intended for use against opponents that are likely to flip the robot.