NHRL May ’22 – The Debut of Omnivore and Bottom Feeder

NHRL’s May event has come and gone, so it’s time to introduce and review the performance of the two bots I built for the event.

New 3lb – Omnivore

Omnivore in its undercutter (left) and vertical spinner (right) configurations. The weapons are fully interchangable.

Omnivore is my new 3lb bot as the next iteration of the design I started last year with Apex Predator. Since this event was restricted to new bots only, this design was made to have interchangeable weapon systems to be able to better counter a variety of opponents. I only managed to take it to 9th place out of 60 competitors in the weight class, but I will take solace in the fact that the bots that knocked me out went very far in the tournament, with one going undefeated all the way through the winner’s bracket and being crowned as the most destructive bot in the tournament.

The central frame that both weapon systems mount into retains the same overall shape, but every part had to be re-engineered to make the modular weaponry possible, as well as implementing a few upgrades.

  • The overall shape of the design remained the same, but all of the UHMW parts went from being solid in Apex Predator to being highly pocketed in Omnivore, reducing their total weight by over 30% to free up weight for the modular components.
Solid Armor from Apex Predator (top) vs swiss cheese armor for Omnivore (bottom)
  • The portions of the uprights where the bar mounts to the frame were upgraded from 3/8″ thick to 1/2″ thick to better take the force of the upgraded weapon.
  • The “bunny ears” at the front of the frame which hold the weapon off the ground while inverted were one of the parts most likely to be damaged enough to require replacement, so they were upgraded to be a separate replaceable part to obviate the need to replace an entire upright if this small section was damaged.
  • The portions of the carbon fiber top and bottom plates that connect the wheel guards to the main frame were cut down to allow larger wheels to be used for the undercutter configuration.
  • The weapon uprights were modified to allow the two plates for the undercutter to key into the frame for mounting, and to provide an additional set of mounting points for the larger front wheels to fit in.
  • The drive gear motors were upgraded to a lower gear ratio to increase the top speed, and uprights were improved to have the motors mount directly to them to make them easier to replace if damaged.

The vertical configuration still uses the same Fingertech beater bar at its core, but with the majority of the components upgraded.

Fork configuration
  • The tooth screws were replaced with asymmetrical AR500 steel tooth plates, increasing the inertia of the bar as well as the durability.
  • The timing belts that I have repeatedly lost in matches before were replaced with more reliable 2L V-belts and custom printed pulleys.
  • A TPU belt guard was added to attempt to shield the belt from some damage
  • The grade 8 bolt that the bar spins on, which has a tendency to bend under strong hits, was replaced with stronger alloy steel bolts.
  • The stock motor and ESC were upgraded to more powerful versions.
  • The battery was upgraded from a 850mAh LiPo to an 1100mAh LiHv battery to give me a higher voltage as well as enough capacity to run at full throttle for the entire 3 minutes without running out of power.
  • The forks were switched from AR500 to titanium for weight, and their mountings were adjusted to prevent them from tucking under and propping my wheels up like in the last event.
  • The printed wedges intended to help combat opponents with horizontal spinners were upgraded to also guard higher areas as well
Wedge configuration

The undercutter configuration took it’s initial inspiration from my older 3lb undercutter design, Portable Apocalypse. Like Portable Apocalypse, the weapon shaft setup mounted to two metal plates with the end of an inverted brushless motor being used to drive the weapon. Unlike Portable Apocalypse, the limited space for the weapon module (and limited selection of small 2L belt sizes) did not leave me with enough space to use a belt reduction to drive the bar spinner this time, so I made my first attempt at driving my weapon with gears instead. The additional space needed under the frame for the undercutter was more than was available in the design for Apex Predator, so I also had to go to making some larger wheels to give me the needed height. Because I didn’t want the bigger wheels to drastically change how the bot drove from the other configuration, I also increased the tooth count on the wheel pulleys to increase the belt reduction ratio and keep the top speed about the same.

Undercutter configuration

Lessons learned

  • Based on my two matches against two opponents armed with the now ubiquitous Fingertech beater bar, at least one effective way of countering the widely used weapon is to build a better beater bar yourself. I was consistently able to win the weapon-on-weapon engagements, and the improved bar configuration now has enough power to bounce the opponents off the ceiling on good hits.
  • I need to make absolutely certain that I loctite EVERYTHING that I can. I initially forgot to loctite the threads on the bolts that serve as the axles for my wheels, and it almost cost me my first match after one of the axles simply fell out of its own accord simply from being backed out by the rotating of the wheels.
  • The TPU belt guard served to protect against grazing hits from two beater bar opponents, but failed to stop a direct hit from an opponent with a single disk from cutting straight through the belt.
  • I need to better pad my receiver, as the same hit that severed my belt somehow managed to jar my receiver (all the way at the other end of the bot) hard enough that it seems to have sheared the processor chip off of the receiver, fully disabling the bot.
Receiver IC apparently sheared off by impact forces
  • I need to figure out a way of protecting against hammersaws, as one opponent was able to slice directly through my top plate and break my receiver in half to disable me in one hit.
Damage from the hammersaw of Saw Loser 2
  • I may need to look into a mini-bot to accompany the main bot, as they seem to be very effective in harassing opponents, and the NHRL weight bonus makes them easy to add in.

Future plans

The 4wd drive system, frame, electronics, and weapon systems seem to be working very well. I feel like I may need to redistribute weight somewhere to beef up the defenses in some places to make the bot harder to knock out with a lucky hit. I also want to improve on my interchangeable weapon modules to be able to swap them out more quickly and with less disassembly necessary. I also think that I will be looking into making a hammer saw module as another weapon option.

New 12lb – Bottom Feedeer

12lb Bottom Feeder, ready to fight

Bottom Feeder was my new 12lb undercutter bot, and the spiritual successor to my last 12 pounder, Antisocial Distancing. I managed to take it all the way to 4th place in the competition, qualifying me for the invitation only finals event in December where I could compete for the grand prize of $12,000!

Three of the problems I had seen with Antisocial Distancing were an unsatisfactory amount of driving control with the 2wd setup, inadequate systems to power the weapon, and a frame that wasn’t holding up as well as I hoped. The driving I improved by going to a larger version of the belt driven 4wd setup that had worked so well in Apex Predator last year. The weapon power I improved by switching to two smaller motors with larger ESCs to drive everything, and large toothed gears to transfer the torque. The frame I completely redesigned with durability in mind. It has laser cut aluminum side and back walls, thick UHMW rear armor, carbon fiber top and bottom plates, and a billet aluminum front bulkhead meant to take the punishment from both my opponents as well as the weapon mounted to it.

Lessons learned

  • I need to figure out the best way to mount the weapon to the gears, or at least bring more spares. I had an aluminum gear to securely mount the disk to, but a bunch of the teeth got taken off in a direct hit from another horizontal spinner. My spare gears were all UHMW plastic, and while they spun things just fine , any hit from a vertical spinner was enough to rip the screws out of the plastic and send the disk flying.
Aluminum disk gear after taking a direct hit
  • I need to find a better way of mounting or protecting the weapon motors. All 3 motors I brought wound up destroyed, with the forces I placed on the motor cans being too much for them to survive for long.
  • I can’t rely on the motor retaining clips. This probably fed into the previous issue, but all of the motors quickly lost their retaining clips on the shafts, leaving them free to drop down into the spinning disk/bar and further expose themselves to impacts.
  • One motor was actually enough to drive the disk in a pinch, but having two for redundancy and spreading the load was nice.
  • Next time when I am taking the motors apart for epoxying, I should also take the time to drill out and tap the holes on the end of the can for larger fasteners.
  • I may actually have the drive setup too fast for my current driving skill level, so I might tone it down a bit for next time around until I get more experience.
  • The frame and drive were extremely durable and don’t have much need for improvement. In my last match I quickly lost my disk again without a spare aluminum gear, but the rest of the bot just kept on running and coming back for more punishment for the full 3 minutes. Give me a spare aluminum gear and another spare weapon motor and I could have had it ready to go for another match.
Bottom Feeder after a punishing final fight. Beaten and bruised, but not broken.

Future Plans

Bottom Feeder will be back, and looking much the same as it did at this event. The weapon mounting and weapon motor mounting could use a bit of improving, but other than that I am very happy with how this bot held up. It’s nice to take a leap on a bunch of design choices that are new to you and largely have things work out exactly as planned.


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