Don't trust CAD; I weighed everything in Mr Mangle down to .1 grams and its still 50 grams from the real weight. Unless you modelled every cable tie and solder joint, CAD is just an educated guess. Excellent video BTW, C3 is looking very threatening! Does it drive inverted?
Front end is 8mm Gr5 Ti. Eat your heart out!Originally Posted by Eventorizon
you checked the data logging Alex? Be interesting to see the start-up current, and amp draw at full speed...
Its been a while but finally things have settled after the champs and I have been able to sit down and examine both robots.
Binky was in a fit state after the champs to also do fleet, basically because she never really fought. At the champs one of the bulkheads broke, a thin walled section that held in the weapon bearing finally broke. This has been replaced with a 8mm thick plate, which is partly recessed into the original hole, that we got welded on. Its a little too thick to get all the needle runners in so we will skim it off and she will be as good as new.
Binky was also fitted with 8 small magnets this year, positioned around the wheels. This seems to have help reduce the moments where she waggles one side in the air, and makes driving her much easier.
However, something has happened that I never thought possible. The massive disc has cracked, probably all the way through. This is at the thick rim section which is a massive 25mm by 20mm of solid D2 tool steel. When we actually looked up D2's properties it turns out its about as tough as cheese (exaggeration but you get the idea). The Americans favourite S7 is around 6 times tougher than D2. D2 is also only around 8% harder than S7, the case hardening did help but it seems that may have been its undoing allowing the crack to propagate all the way round and then into the material.
My thought of when this happened was the gladiator. When Binky's weapon belt snapped Galactus drove straight into the stationary disc, probably hitting it so hard that it deformed and snapped. We are going to attempt a repair by grinding down deep where the cut is and then filling the resulting groove with a massive weld, but this disc may have had it.
However, this does mean I can design her a new Disc! I have several special designs in mind for various materials and robots so watch this space!
Now, Conker 3 was mechanically OK after the champs. Everything functioned but from the massive hits it dealt out and received she isn't going to be running for a while.
Issue 1 is that the weapon itself is about as square as a banana. I hit massacre's bar so hard that not only did I bend his up at around 30 degrees but also twisted my own weapon. This resulted in the bearings on one side exploding every match after that; tapered rollers do not like being off angle! I will have to get a new, stronger weapon cut and I will be using deep grooved bearings from now on: much cheaper and more willing to be misaligned.
Issue 2 is the damaged caused in one hit by 720, snapping the rear bar and twisting the Hardox armour. It couldn't have been any worse really. The armour was never designed to take a hit in that direction and it was at the perfect height for 720 to hit it at full force. The robot actually flexed so much in the hit that my weapon hit the bulkhead, taking a thin chunk off one side. It even had enough force to turn the holes in the titanium into ovals but that's not a problem when I cinch all the CSK bolts up tight.
Once the Hardox is bent back into shape and I have machined a new rear bar (I am definitely going Grade 5 Ti) she will be ready to fight again.
Unbelievably the 3D printed drive system survived the entire event unscathed! Nothing broke! Given it saved me around 200g in aluminium pulleys and wheel mounts I am defiantly keeping that for next year. As for the 3D printed battery mount, I might have another stab at it. I may try wrapping it in fibreglass or dipping it in some kind of resin with fibres in to prevent it from cracking along the build lines. The alternative is welding a Titanium one directly to the base plate, much stronger but far more permanent if I have to modify it.
Overall, it could have gone much better but at least this time I am not doing a total rebuild on Conker like the previous 2 years. Conker 3 is a far better machine than the other two, and once I get all the kinks ironed out I am sure I can get her seeded. The same goes for Binky, but after everything that happened this year nothing is out of the question once a fight starts!
Sorry to hear about the disk fracture - D2 is a wear resistant steel with really poor impact resistance, although I never heard about the 6x comparison to S7 before. Case hardening would only have helped to promote fracturing by raising the surface hardness and welding it up will likely just delay the inevitable. The best options are to get a softer disk in some type of Hardox or to go all out on an S7 disk that will last longer than wear steel but will cost a fortune. The S7 beater in Mr Mangle cost around $700 USD back in 2007 and its WAY smaller than Binky's disk
We are looking at one disc made in Stainless steel for machines with plastic or aluminium armour, and another disc made of a steel called H13 for Hardox and Titanium machines. We have various treatments we could do on the part once it is machined
The exact details of the 6x refers to impact toughness in a Chappy C-Notch test, (ft-lbs) where D2 comes out with around 20ft-lbs and S7 around 120 ft-lbs. H13 is up at 145 ft-lbs.
When looking at Rockwell hardness:
D2 = 63
S7 = 58
H13 = 52
There is a distinct trade off between Impact Toughness, Hardness and wear resistance. H13 has the highest toughness, but the lowest harness. D2 is the opposite and S7 sits in the middle. The disc needs to be hard so it doesn't deform but if it cant take the shock loadings of a hit then its just going to snap. This is just one very expensive balancing act.
Simple solution , Hardox 650.
If hardox 650/extreme blades can cut rebar concrete like a candybar or hardox 450 like a piece of cheese grade ali, it will do the job for most applications, and if it's not something something, that's brittle.
The only problem with using pre-hardened steel like Hardox is machining it like the broken disk; you can waterjet the profile but cutting the tapered tooth and the thin spokes would be difficult. Waterjetting a thinner disk is easy enough, but you will have lower KE for the same weight.
Comparing H13 and S7 steel, the S7 has the impact resistance needed in a KE weapon and the trick to getting the most out of it is to NOT harden it to the max. The US guys harden to RC 50 to 54 and that gives it even more toughness. Another critical thing is to use a heat treater who is familiar with the steel - I made a part in S7 and had a local shop do the heat treating. It came back super brittle and I am pretty sure they didn't anneal it properly, if at all.
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