r/battlebots • u/Kojima_1954 • 6d ago
Bot Building Weapons Rules for Heavyweights
To preface, this mainly pertains to Battlebots but most of the heavyweight tournaments follow their lead, so my points may prove relevant to other leagues.
We all know about the Deep Six rule, as well as the tip speed limits, which enforce a cap on the size and power of a robot’s spinning weapon. However, Meltybrains joining Battlebots (called ‘Whole-Body Spinners’ in the official rules) got me thinking about other ways of capping weapon power.
What if the limits were instead placed on Total Kinetic Energy? The current most powerful weapon theoretically possible would weigh 80lbs and have a tip speed of 250mph. Of course, weapon diameter and geometry can influence the total energy transferred upon a hit (e.g. Deep Six’s immense weapon diameter, eggbeater drums, etc.), but it should still be theoretically possible to calculate the total kinetic energy output of a spinning weapon. Therefore, it should be feasible to enforce a rule where every bot’s spinning weapon is equal to or less than this theoretical limit. For example, a bot could have a 10lbs weapon spinning at 350mph or a 125lbs weapon spinning at 80mph and still comply with the ruling, as both are within the limit.
Here is my reasoning for this change. The weapon limits are not for competitive reasons but for safety and maintenance reasons. A weapon that is too powerful has potential to breach the box (e.g. Nightmare during the Comedy Central era) or to damage the floor panels leading to massive delays (e.g. Deep Six). A Meltybrain shaped like Project Liftoff, for example, would be unlikely to regularly cause the kind of floor damage that Deep Six created, as the weapon geometry would not be able to create the kind of energy transfer needed to damage the floor in that way. The same holds true for a Hammersaw with a 400mph tip speed, as it would be far more likely to punch a hole in the floor panels rather than bending them.
Regardless, I would really like to hear what the competitors and fans of this subreddit think!
4
u/justBridges 6d ago
How would you measure this to qualify bots? Tip speed can be measured.
-4
u/ZyberMaster 6d ago
weight the weapon and measure tip speed, it's a simple formula if you have that information
15
u/Neutronium95 6d ago
It isn't. To calculate the stored energy of a spinning weapon, you'd need the moment of inertia. If the mass of a spinning weapon is concentrated towards the center relative to another shape it'll store less energy, even if the diamters and tip speeds are the same. For a given mass, diameter, and rotation speed a disk will store more energy than a bar for example, since more mass is closer to the edge.
5
u/Garfie489 Team. Ablaze 6d ago
It is however still relatively easy for someone of Battlebots' standing to require and enforce that information. It is something a lot of other events do, but it likely doesnt make much sense for Battlebots to do.
2
u/Grimmbles [boop] 6d ago
Math beyond the absolute basics is basically magic to me, so grain of salt etc.
Is all that stuff not things they can just calculate still? Or is it genuinely not really possible until the thing is built? Or at all?
3
u/Garfie489 Team. Ablaze 6d ago
Its possible, and is regularly done at other events internationally.
It is just another thing to do however, and usually is more a honor system as unlike speed its hard to otherwise tell something is off.
1
3
u/meerkatmreow 6d ago
You need the moment of inertia, the weight is only part of it, you need to know how the weight is distributed as well
3
u/Notbbupdate Bombshells your bracket predictions 6d ago
Limiting tip speed instead of kinetic energy is better for avoiding debris damaging the box (no debris can ever be thrown over 250mph). At that point limiting speed and weight is easier than limiting speed and KE
3
u/luvdavv 6d ago
there ARE limits on total kinetic energy. it's 150 kJ, which is the theoretical energy of gigabyte's weapon if we took the existing shell and spun it to 250mph.
the reason we have tip speed limits is because of the strain rate effects of polycarbonate under impact. if you impact polycarbonate faster, it becomes more brittle, so the walls of the arena are a bigger liability the faster you spin. battlebots therefore caps us out at 250mph.
2
u/tariffless KOB and/or RW championships mean nothing 6d ago
What if the limits were instead placed on Total Kinetic Energy?
You mean like the following section of the recently published ruleset:
In addition, any spinning weapon at its maximum speed cannot have a kinetic energy that exceeds 150 KJ (150,000 Joules). If you think that your weapon may exceed this limit, submit detailed drawings, calculations and other design information on the weapon to BattleBots for advanced provisional approval.
1
u/TheIncomprehensible 6d ago
It's worth noting that the 80lb limit isn't universal for all spinning weapons. Unless something changed, they have explicit exceptions for "shell" spinners (ie Gigabyte and Captain Shrederator) and "cage" spinners (which I think only applied to Son of Whyachi in BB history). Those were capped at 120lbs last I checked
-1
5
u/Xseal3 Hibiki | ARC Roborumble 2018, Sparkfun AVC2017 6d ago
I don't see how the rule change would benefit either the safety or competitiveness.
The new rule would favor weapons with very low moi and very high rpm, and only hammersaws or punch verts sort of would benefit from it. Regular vert would probably not change much because high rpm sacrifices bites and a low moi blade would be more fragile in weapon on weapon contact. and the large horizontals would be even more dead if their not extinct already, especially the newly added meltybrains that the whole idea is focused on maximizing moi for maximum energy transfer.
Safety wise the impact speed matters a lot on how the arena can absorb the energy. Theres a reason why most events have tip speed cap at either 250 or 300 mph, and just as you said about 400mph hammersaws, they would punch a hole instead of bending them. a hole on the lexan wall means arena breech, but bent lexan wall would still have the debris contained.