The front wedge for my featherweight combat robot. 0.5" 4140 steel sitting at a 30 degree angle from the floor.
Nice wedge! Just wondering why make it all out of heavy old steel when you could save some precious weight by making the majority out of aluminum then put a top plate of something even harder than 4140 Steel and have it weigh less and be slightly stronger at the same time?
Solid materials typically fare better in a combat environment.
Plus, it’s pretty thin as it is.
OP - you better post a picture of the final robot! This looks pretty cool.
To play devil’s advocate: 4140 could he heat treated to at least 55 HRc. Though I imagine the toughness and ductility of a lower hardness are desirable in this application.
There is a Facebook group called Combat Robotics. It’s full of discussion just like this. I would definitely recommend checking it out if you haven’t already!
Because the shop had a bunch of 4140 in the scrap closet. I’m trying to keep a low budget with this one (despite the weight of the wedge and drum, I can still get away with 1" thick aluminum for most of the frame 
Will do! Do they have any good resources on drum-in-wedge designs?
S7 Tool Steel is really tough stuff. Rockwell up to C53 & 273 Ksi yield strength. This material is the used for jack hammer tips as well, so it can take a beating.
How does 4140 compare? Or is 4140 s7? I don’t know my steel alloys all that well yet.
Wouldn’t you be better off tapering the top edge further back (to make it a lower angle)? I would think the lower the angle the easier it would be to get under an opponent.
Is this being designed for a specific combat robot competition, and if so, which?
I’m not all that concerned about the taper seeing how it’s already capable of peeling paint/tape off the shop floor. Also considering current design trends (armored front, no side skirts, open wheels), there really arent a whole lot (if any) of robots this couldnt get under
I plan on competing at motorama and robogames.
This seems to be a guillotine blade. What does it weigh? How does that compare with the original?
There are really four classifications of steel.
**Plain Carbon **(such as 1018)
**Alloy Steel **(Such as 4140)
Stainless Steels or Chromium Steel (410, 440C)
Tool Steels which are Alloy steels with a high carbide content. These typically have Tungsten and Chromium as alloy elements with others. These are typically used for cutting tools for other metals.
At work, we target ~40 HRC on 440c components that have high loads and require some hardness. At 40 HRC components will deform quite a bit before cracking, it eliminates the insta-cracking. Not sure about 4140, but its probably in the same ballpark.
The original what?
Wedge weighs 3lbs, drum weights 8lbs for a total of 11lbs.
Once you check it out you’ll find tons of content specifically relevant to your design, plus hundreds of experienced people willing to offer advice. In a way it’s comparable to CD, but specifically for fighting robots.
The link was to a picture of an original guillotine blade, used during the French Revolution, now on display at a museum in Paris. That blade weighs about 20 pounds.
I never understood the rational for having exposed wheels, I feel like it’s just begging anything with a blade or a spinner to take a wheel or two off and immobilize you (IE basically every match with “Stinger” on BattleBots). Is this all just due to weight limitations or is there some other benefit to having open wheels I’m just not seeing?
Open wheels allow you to have a wider and longer wheelbase which can help with stability and reduces your chances of getting high centered. Another big issue with wheel guards is the chance of them getting bent in a way that they lock up your wheels. A great example of an open wheel bot is original sin from robogames or Yeti from battlebots.
Part of the reason Tombstone has open wheels is because the builder knows that most people will try to go for them. This leaves them open for tombstone to quickly rotate into them by using the yaw effect created by accelerating the blade. The wheels aren’t actually the weakest part of the robot. The biggest danger to tombstone is itself.
It’s just easier and lighter than having wheel guards. The trend nowadays is asymmetrical vertical bar spinners (similar to a personal favorite of mine, Bugalele).