I'm getting more serious about a combat robot design I've been contemplating for several years now (BattleBots, Robot Wars, etc) and find myself overwhelmed by the sheer variegation of ASTM and AISI grades and alloys. I hope that by detailing the application, those familiar with the nomenclature can steer me in the right direction.

The overall design is a full-body spinner - somewhere around 0.75m in diameter, at least 2500 RPM. (Approximately 205 MPH weapon speed, though this is a minimum target.) The circumference is lined with five or six solid-mount blades approximating the size and shape of forestry mauls, though slightly thinner - while primarily relying upon inertia and brute force, I would like to retain some degree of sharpness/cutting.

Structural integrity is the key attribute, remaining intact (if deformed to some degree) in spite of high-speed impacts with fixed hazards, opponents, and/or similar spinning weaponry. Any significant separation would be of serious concern owing to the high-speed rotation.

The blades will be mounted to the outside of the body with high-strength bolts, anchoring roughly half the length and 60% the mass of each individual blade. (I have no intention of ever welding these pieces as even a fractured blade would be swiftly replaced.)

Withstanding impacts and remaining affixed with minimal distortion is highly desirable. Retaining a sharp edge would be nice, but this is mostly wishful thinking - for the sake of other traits, some sacrifice must be made.

What little I understand of this sort of metallurgy has me looking at ASTM-S1, which seems to be recommended for high-speed impacts and sudden shock-loading. (Also assuming those terms mean what I think they do.)

Any guidance/recommendations in this department would be greatly appreciated.

  • "What the other guys use" tend to be 'trade secrets' - understandable, as even a slight advantage can be crucial. Around $2500 anticipated total budget, though I'm sure it'll be more. (Though, as these are 'disposable' and replaceable, I'd definitely prefer a cost-effective approach.) – Twyla Naythias Fox Aug 14 '17 at 17:48
  • "Blunt" and "cutting" are diametrically opposing concepts. But if you want to learn how to make a strong and sharp blade, join some of the knife- and sword-maker clubs. Those guys create frighteningly powerful cutters. – Carl Witthoft Aug 14 '17 at 18:34
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Answer 2: Because you are not building thousands of the Bots, You need to look at materials that are already heat-treated for strength and toughness. Just thinking of the material and not the form : rear axel( of rear wheel drive ), Torsion bars , leaf and coil springs. Construction equipment ; bulldozer blade ( edge if it is separate material from the bulk, bucket teeth ( if replaceable ), bulldozer treads, blades/arms of big chipper shredder ( hammer mill ) used to chop tree trunks ( Asplendunk is one name). The chipper is almost what you are making. These are educated guess ; all likely have more carbon than optimum for toughness. But it gives some ideas where to look.

  • Ooooh! Right! Part of what inspired this design was an odd axe/maul-hybrid kind of tool my great-grandfather had - he used it for firewood but I used it to hack apart a 1964 Ford Falcon lickety-split! But that tool is long gone; don't even recall if there was a brand ID on it. – Twyla Naythias Fox Aug 16 '17 at 15:34

S-1 is not an ASTM designation , likely AISI tool steel designation ( likely it is included in some ASTM spec for bar, ). First , what do the other guys use, no use re-inventing the wheel ? Second , is cost a concern? Third, is heat-treating a concern? I would stay away from tool steels ; "all " tool steels primarily hold an edge. So grades like S-1, S-2, H-11, H-12 etc, are the toughest among steels that are intended to hold an edge. And you will pay a premium for "tool steel". Most of these have about 0.5 % C; C generally lowers toughness. I don't think any contain nickel ; the first alloy you add for toughness. So, I think low alloy steels with medium carbon would give maximum toughness with some hardness. ( AISI/ SAE) 4330 > 8630 > 4130 ; These have 0.3% carbon and are listed in descending Ni content. When quenched and tempered a good one may stop a Charpy hammer ( 240 ft.lb) ( standard toughness test). Also things like 4320 with a carburized case could be used.

  • Second case hardening. Pick a ductile steel with high toughness and case harden it. Outer case is hard and wont get easily damaged, interior is ductile to prevent shattering etc. – starrise Aug 14 '17 at 3:21
  • Make one - follow the procedure for the samurai swords - soft inner and hard outer... – Solar Mike Aug 14 '17 at 5:57

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