Before I began to hone the construction of vertical spinners, I have long enjoyed control bots. Control bots are critical to any good builder’s design philosophy because while it removes some easy advantages, it expands your mind to think of other aspects of combat such as solid construction, excellent driving, and other methods to attack your opponent. It is good to have a damaging weapon and is critical to any of the top machines in any weight class, but few situations develop your skills as well as honing a good control bot (just ask Kevin of Claw Viper!)
Now with the preamble done, onto the robot! From the beginning Fracas was designed around the methodologies of two robots: Sawblaze and Claw Viper. Sawblaze’s wide structure is perfect for capturing other machines and Claw Viper’s jaws are one of the best lifting systems. Claw Viper’s jaws (based off the Chinese machine ‘Greedy Snake’) are an excellent choice for a lifting system in particular because the lower jaws act just like normal forks when uncompressed but become powered as the upper jaw closes. This will be revealed in greater example as the bot develops, but because of this ability they protect the main lifting mechanism well and are critical for ground game.
This robot is also practice in welding as the primary means of construction. While more common in the 250lb class, welding is rarely seen in smaller machines despite its incredible use in manufacturing throughout the world and AR500’s much higher strength than Aluminum alloys. Steel construction is also different as NHRL has welders on site for builder use so the ability to quickly cut and weld in new pieces is a new idea of how to maintain machines. Through trying out this process on Fracas, my welding skills and familiarity with steel would increase allowing for much better support while fixing heavyweights and better idea of how to apply this method in any future designs.
Once the designing was complete, the construction of the robot began. Instead of hopping into a full welded box, I sought to create two steel weldments held together by bolts as to allow easier maintenance, largely inspired by MegatRon. After cleaning the tabs on the parts, the chassis easily slotted together and was TIG welded into shape. The chassis is mainly 3mm AR500 (same goes for the jaws) but the central rails were 1/4″. Overall the process to get the chassis from a flat sheet into a 3D shape was only 3 hours, a incredible speed leap over the many hours of CNC milling and tapping that go into an Aluminum frame.
In contrast to the steel construction before it, the 1in thick 6061 Aluminum took awhile to machine on the router. While it was good practice using machine vises on the router, I was hesitant to try a second operation to remove the bit of material still being held by the vices so I used a combination of band saw and sander to make the edges as flush as possible. It was not perfectly flat, but it was within acceptable tolerances of the machine.
To drive the lifter, the plan was to use a 64:1 Andymark 57 Sport gearbox that later drives a #35 chain drive from a 10 tooth to 23 tooth sprocket. However, because the output shaft of the 57 Sport is 1/2″ hexagonal and the bore of the sprocket is 1/2″ round I had to use the mini lathe to turn it down to match the sprocket. A little bit of hex remained to act as both a natural spacer for the sprocket to rest against and to retain the shaft in the gearbox. The grub screw in the sprocket was used for primary torque transfer. The output sprocket was leftover from another project so it had a 5/8″ bore. To minimize the cost, a small bit of 5/8″ keyed shaft was bored, and inserted between the sprocket and shaft. The sprocket was then welded to the output shaft to ensure all power is transferred to the lifter. Usually a mechanical clutch would be good here to avoid damaging the gearbox, but for this machine I plan to current limit via the Maytech 100A VESC controller (also leftover from an old project) to ensure no mechanical issues while lifting and allow for tuning in case more current is needed.
Also note that the lifting shaft itself is retained by shaft collars that are welded to the frame rails themselves. The shaft collars are 5/8″ bore with bushings that have an 1/2″ bore. The shaft rides in these bushings, allowing the system to rotate while the shaft collars still keep the system retained. It proved an excellent feature as nearly all force for arms is downwards (into the steel welds) and never upwards towards the bolts.
The wheelguards were also printed out in Sainsmart TPU with ~14 walls and 15% infill. After testing with Vorion, the idea of thick rubbery walls that can still squish proved very effective for defense and so were adapted into Fracas. They were retained by 1/4-20 bolts into the thick aluminum frame rails. The lifter system was tricky as the idea was to still make it serviceable despite the need for high torque transfer. Since I did not have access to broaching set, the only solution I could make was 10-32 set screws aligning to the keyways. In theory this allowed the head system to be taken apart and serviced as necessary.
Here you can see the lifting system at work. The lower jaws ride on bearings so they do not move, allowing them to act as passive forks. However, the upper jaws are welded to the output gears allowing them to be driven by the chain. Those upper jaws are on the body of the lower jaws, forming a leverage point that, when the upper jaws are locked, allows the lower jaws to then rotate and pick up whatever is in the jaws’ grip.
Here you can see the jaws at work as it picks up a helpless Demogorgon.
Here the upper jaws were formally welded together and the safety lock added. Steel is so convenient to to add stuff to: cut some pieces from stock then just stick it wherever you can fit the torch! Still need to make some room for the safety lock though as being that close to the jaws isn’t the best to hold by hand. The top plates were 1/8″ G10 Garolite as they have an excellent stiffness to weight ratio.
A simple wide horizontal wedge was made, though a very crude design. The process of using a TIG torch to heat select parts of the 3mm AR500 to bend it was a great skill to keep in the back pocket, but I also realized this wedge was way too weak to handle a real 30lb horizontal so it remained in storage for now.
Motorama 2023
Fracas’ outing at Motorama was underwhelming as the Flysky system worked very poorly in the arena. No idea why that was the case, but it did make the robot only respond sporadically in the box which didn’t let it test anything. The little bit of movement it did have was frequently getting stuck in the arena with the sharp fork tips so I learned to round off the edges some to allow it to move more smoothly. This will be a helpful trip as I look forward to March NHRL.
Since Fracas was headed to the glittering world of NHRL I decided to spritz it up a little by adding a purple backing with gold fleck to add to the more “chaotic” nature of its name. It turned out well! Steel bars were also added to the front of machine to avoid its heavy wheelying issue that turned up in testing. The internals of Fracas are the same as Phenomenon/Vorion so the Robocore wheels got too much grip and made it wheely all the time. These bars were overkill but effective in balancing things out without making it to heavy one way or the other.
After the event, I developed a new horizontal wedge with much better bracing that should handle all the mean horizontals coming. Unfortunately this required a way to service the jaws to ensure that the lower teeth would clear it and there was not enough weight to simply make the wedge longer. Later I learned that the set screw system in the drive gear had fused with the keyed shaft so the lower jaw near the sprocket was trapped between the gear and the sprocket so if it was messed up there would be no way to service it. To make the system last a little longer, I cut down the jaw so it would avoid being hit in fork mode and sit behind the horizontal wedge. The other arm then received a flat, wider face to hopefully feed more robots into the jaws and was thickened to 1/4″ to hopefully resist more impacts.
March NHRL 2023
At March NHRL, Fracas had a wonderful display of its abilities though not without some damage. It turned out the welds were a little sparse so many had to be fixed on the spot. The main thing was the lifter assembly which was now formally fused together via MIG welding and one of the front fork supports that had to be fused together again in the same way. All in all nothing was wrong on the machine as it only was knocked out of the competition by forfeit to Phenomenon to setup a Phenomenon v. MegatRon final. Later I found the front springs were crushed by a strike to the fork compressing the spring so fast it was smushed more than compressed. In general, the bot was in good shape.
May NHRL 2023
Fracas quickly went from good to very damaged very fast. In its one great match of the event against Ripperoni, every weak point in the robot was revealed, namely weak arm structure and strikes to the chassis. The arms were definitely more fragile than I liked, but Ripperoni made sure its issues were proven. The weak 3mm arms only held by 1/4-20 bolts easily sheared away by the blade and the strike to the rear messed up the AR chassis.
While the steel chassis could allow me to repair the machine, the destruction was too great on multiple fronts to be done on that timeframe, especially without more sections cut with the right hole pattern.
These gorgeous photos are courtesy of JCRB Photography.
Post-Mortem
Now that there was some time to breathe its time to really try out that steel construction! After cutting off the mangled piece and smoothing out the area as much as possible, I pulled some scrap 3/16″ mild steel and cut it into about the right shape. The hole patterns on the baseplate are mirrored so I used the other side to mark locations then drilled them out on the drill press. A little bit of grinding to clean the surface then the TIG torch was off joining the pieces together. All in all the process was pretty simple and took only a little time. It wasn’t a perfect drop in since there’s still a bit of angle on it, but I could easily see it being a big fix in a pinch.
After cutting out the chassis the arm was cut out too. The entire assembly was ruined so a perfect time for a clean slate
Lifting Arm V2
The new lifting arm system was designed with the goal of modularity in the system while also leaning into the durability of the system. The first move of that was to reinforce the head via cross-bracing on the top and bottom of the jaw. Though it removes the ability to service the head, the understanding is that if the head is damaged it would be faster to replace it as one full system especially because the gear works much better to be directly welded to the head itself. The next step is to have the whole system slide over a hex shaft as the hex is a very strong transfer geometry due to its spreading the load over a larger area than the keyway. However, it was very clear that the best torque transfer method for the sprocket was also welded to the shaft. To get around this fact, the sprocket-side arm rides on a round area larger than the hex while the outer arm rides on a smaller diameter that bumps up to the edge of the hex. To ensure the at the geartrain has the hex pattern cut into it, they are all made from 1/4″ lasercut AR500 that are then aligned using 2x 1/8″ dowel pins which are then welded off at the end to make it act as one piece. The lower jaw thicknesses were also increased to 1/4″ to better resist impacts.
After a long series of building, the majority of the arm comes together. A combo of turning and welding gets the assembly 90% together with the sprocket as the last piece to assemble. The main issue with this is not properly checking the alloy of this main shaft. This was a foot long 1/2″ hex material bar found on McMaster made from 12L14 material. The common material options such as 4130 or 4140 were not available in the right size so I assumed based on strength figures this material would be suitable. Unfortunately, a little deeper digging would reveal that this material is ultra machinable due to a small percent of Lead being introduced to the composition. This then makes welding a terrible idea idea as it both does not form strong bonds to carbon steels and vaporizing the Lead which is horrible for a person to breathe. This was only learned in retrospect but its a valuable lesson on checking all bases.
After trying (though mostly failing) to connect the pieces together, the main connection assembly was made. Another head was assembled as well.
August NHRL 2023
August NHRL was a rough time for Fracas, but still successful. Though it ultimately lost to Synthesis sliding in its teeth, the rest of the robot did well, especially in its control of most machines. This was a very annoying moment as I could likely have just kept nose-to-nose with Synthesis the whole fight and maybe played the control game to a Judges’ Decision but I was greedy. The good news was the horizontal wedge was effective resisting Depth Charge and Ester (horizontal part of Polyester) so that design is encouraging for the future.
BBB BEVS September 2023
Due to a number of unique factors, a door opened to go east to the United Kingdom for the first time over seas! After some work bending and rewelding the chassis back into place, a new top plate was made from 1/8″ Polycarbonate. Additionally, the metal tips on the bot were covered in 3D-print to resist scratching up the floor.
The BEVS competition is Sportsman-based so it was perfect for Fracas to attend. The competition was based next to the Left-Hand Giant Brewery so it made for a very relax atmosphere as opposed to the traditionally more serious competitions I’ve attended in the U.S
Ultimately the bot’s great issue was the 12L14 material used for the hex shaft. Though it lasted through the August competition, the welds cracked almost immediately after its first fight so Fracas served as a purely drive robot the rest of the day. Despite that, the battlehardened drivetrain propelled Fracas to a 3rd place, only losing to the eventual champion of the event! You can see Fracas’ fights and how it got the green ball pit trophy here. All in all, a great time enjoying a different robot scene and hopefully a connection point for more events in the future!
Pre-NHRL Finals Prep
In order to best prepare for the incredible rigor of the Finals, the creation of a 2nd Fracas was critical to best service it in time. Starting from another palette of parts, a 2nd Fracas was quickly put together and a new 57 Sport output shaft was modified. The primary improvement of this machine was the direct integration of welded frame rails tabbing and joining the body together. Nutstrips were still used to align the components during welding and remain in the machine as a secondary measure in case the welds fail and there is risk of the front coming off the machine.
Another new experiment I wanted to try out is adding more material around the tip to create a pyramid-type shape through hardfacing. The process is pretty straightforward: heat fork, add filler base, then add hardface over it. The material itself is designed so as it cools it reaches a hardness similar to the AR500 base around it. This method of hardfacing is based around Stick welding where the shielding material is surrounding the material. Unfortunately, that material gets in the way (and I’m not experienced with Stick welding) so it was a very blobby finish as the shielding would flow in between the materials.
After the second chassis was done, the robot was wired up in similar manner to the original and the new jaws were attached. To liven up the machine before Finals, I decided to model it off the Van Halen Best of Both Worlds album.
NHRL Finals 2023
First photo is courtesy of JCRB Photography
Fracas had a rough time in the Finals against Yahoo and Kitchen Grill. The angled forks worked against Yahoo for awhile, but the drive wasn’t perfectly smooth so Yahoo managed to get some hits. Even worse, the primary jaws’ weren’t strong enough to resist bending so as soon as Yahoo caught the jaws they buckled.
Against Kitchen Grill, the TPU guards finally proved their limits. Yahoo’s wide drum teeth and body rubbed against the body, but Kitchen Grill’s narrow and sharp blade cut straight through the guards and hooked the mounting, lifting and twisting the robot more violently than ever before. The jaws of the machine were also struck and crumpled, completely ruining that set of jaws. In two matches, both Fracai were thoroughly beaten, revealing the weakness of the jaw system. In contrast, the main chassis body is very solid with the main steel body being nearly untouched with bending only occurring on the lifting arm frame rails after being directly struck. All in all strong mark in the favor of steel construction for strength especially after being launched so heavily. With this chassis confidence in mind, Fracas ends its run in 2023 and looks forward to 2024!
Bone Dead Robotics 