LOL, that's how you get a machined part - you cast it, then machine it to specs.
The only way to know if something is cast or forged after it's been machined, is to break it open and inspect the grain structure (yes, metal has grain structure)
The grain structure is also what detemines if a metal 'bends' or 'breaks'
Also, ALL forgings start out as cast. You cast the ingot, and work it while it's hot. That's what 'wrought' metal is - it's worked metal. Normally you'd take a large ingot, keep it hot, and basically work it into a billet block. You then machine that block to your specifications, and perform final treating / anodizing, whatever.
You gotta stress test whatever you build, though. Personally, I think that items like the bearing carriers are absolutely fine cast, as they don't see a lot of stress, but you do want them very rigid. A-Arms, on the other hand, you'll have to either make overbuilt to handle the stress of slamming into things @ 60+mph, or design them so that they bend if overstressed.
My 'ideal' RC, regardless of 'shape' would be something like the following:
Metal chassis for rigidity and LCG
Metal bearing carriers
Metal diffs and housings
Metal transmission housing
Metal slipper/center diff housing
Metal suspension links (camber/toe)
Plastic end links (ideally, I would design these so that if you slammed into something and forced the wheel to turn, the rod end would bend, without damaging the rod - rod ends are super cheap and easy to replace)
Plastic shock towers
Plastic body mounts
Look at Jang's durability montages - he very *vey* accurately replicates what these vehicles go through when driven normally.
Front wheel impact:
The shock should absorb whatever force it can, with the a-arms transmitting/absorbing the rest of the impact into the chassis. I'm sorry, but a pillowball pulling through the axle carrier is 100% unacceptable unless the axle carrier fails.
Nose down impact:
Front bumper should take this hit. I really like Traxxas' design on the front slash, with the plastic oval giving quite a bit of flex to absorb shock. I would further want to see RPM redesign that piece, as I would build it thicker to handle even more load.
Y axis rollover (aka the 'cartwheel'):
In this maneuver, you have a lot of things going on. You're going to have centrifigual force trying to throw things outward, with each individual impact with the ground smashing inward. The front and rear bumpers should be absorbing the front and rear impacts, the wheels (and hence, a-arms) should be absorbing the side impact (in the case of SCTs, you also have the nerf bars and body helping with that).
X axis rollover (do a barrel roll!):
The wheels should have no issue here, as the suspension should be absorbing all the bottom impact without difficulty. The body posts and the shock towers have to absorb the upper body damage, though, hence built in flex.
Z axis rollover (endo gone wrong OR shoulda landed that better):
This is one of my favorites, as it's usually a nose down crash gone wrong. So starting from the nose down crash, we have that force on the forward bumper begins to rotate. Here's where your bumper mounts will be stressed (this is the same force that snaps the rear Dominus bulkhead mounts, when you pick it up by the rear bumper without care). As the rollover continues, you move to stressing the shock towers, and the chassis - this is where having a properly designed chassis plate really comes through. If you have a single plate design, you seriously risk chassis damage here, as that plate has no extra rigidity in the Y axis (this is why I do like the Dominus bent plate design - nice and solid). This is also why the MT4 guys do the turnbuckle between the shock towers.
Looking at the current 'big' players in the industry, the only guys I see doing most things right, is RPM.
Traxxas IMHO comes close - they used to have some really nice design engineering, and the LCG Slash / XO-1 show me they still have talent, but I think Traxxas has gotten very complacent up there at the top of the mountain. It's high time someone took them down a peg or two, I think.
Have I bored everyone to death here?
This industry has horrid quality control. Pretty sure the guys that build these don't bother actually bashing them.
(Last edited by uberDoward : 1.15.13 at 2:48 am)