STIFFY chassis assembly... final cut!

[rc4x4nut]

Originally Posted by zeropointbug

hey Gustav, im glad you like it!


I was originally going to make the parts from 7075-T6, but i've read around the web about horror stories that it can just blow about with a bang with not warning. That is of course with excessive fatigue, and, the 6061-T6 is better at copping with fatigue. 7075 would have a clean break, were as 6061 will bend more before it breaks. If i could afford it, i would use 2024-T3 aluminum, this stuff is is like steel, it's light, and has superior fatigue resistance.

Here is another pic of top view. If anyone wants to view a 3D file of the assembly, just let me know. I can email it to you.

zeropointbug

IMO the 7075-T6 would be the way to go if designed right. Look at the supermaxx parts. You rarely ever hear about their parts failing. Beautiful chassis though. I wouldnt skimp out of its design and material. Of course this drives the cost up.

[Gustav]

That mount i was talking about definately provides a lot of protection against big shocks too,the whole assembly is very springy,the bushes are squishy and not done up tight and you can flex the whole thing considerably with one finger.The posts are plastic and flexy and the whole thing can spring about in a tumble,it takes the edge off the blows.It seems to have proved reliable in the truck,in real life.A casio G-Shock floats in a rubber bush i believe,similar principle.

Anyways..the 6061 vs 7075 thing,i've always looked at it like this,(disclaimer,it's just a theory from my little brain);it's possible to make a 6061 part equally strong as the 7075 part at very similar weight,it simply takes more volume of material.7075 is a similar percentage stronger as it is heavier to 6061.So using 7075 is not strictly necessary to get a part that's of similar strength and weight unless you're restricted to paticular dimensions or specifically need the surface hardness,such as in a diff cup where 7075 is required.7075-T6 still seems to bend long before it snaps in RC car chassis,so i'm not sure i'd be worry too much about metal fatique,it doesn't look like it'll be flexing a whole lot.i'd just descide based on strength:weight,cost,availability,machinabilty.

[zeropointbug]

rc4x4nut, thanks!

that's true, i guess it doesn't matter if 6061 is not as brittle as 7075, if it bends, it bends, it still fails. I suppose a bent up part(6061) is just as useless as a broken part(7075)... :007:

I'll see how much difference it will cost on the entire chassis if i made just the bottom chassis plate out of 7075, and the rest 6061.

What do you think, should i go with 7075-T6 for the bottom chassis plate?

It would prob only be $15 more... really. The .25" (chassis braces) stock is too expensive though. If i had ENOUGH money, i would make it out of 6Al 6-6-2 Titanium, ~200,000 psi yield strength. :017: And more flex than a chinese acrobat!

zeropointbug

[zeropointbug]

Gustav, that's true about 6061 and 7075 typically being similar in strength for the "typical" part design. HOWEVER, IF you design it right (which takes skill, and experience, and 'feeling') the stresses (such as impact) should be transfered in such a way as to avoid modulus stress, and basically transfer it as a tensile force. And use the material to it's capability. That would allow 7075 to fully show it's stuff.

6061-T6 typical tensile yield: 40,000psi 2.7g/cm3

7075-T6 typical tensile yield: 83,000psi 2.74g/cm3

2024-T3 typical tensile yield: 70,000psi, 2.77g/cm3 superior fatigue

I have tested the bottom chassis plate mayn times with ALGOR designcheck, and managed to get VERY distributed stress, while at the same time keeping the motto "form follows function", and design dictating functionality.

triangulating, circular coring, and tapering are the main features you want to keep in mind, and the most important part, knowing how to apply, and integrate them.

So i think 7075 it is then...

zeropointbug