Quote:
Originally Posted by TheModMaster8
if i remember correctly so don't take this last part as fact... i believe it requires the for needed to bend the flat plate plus the force required to bend the two walls hight wise.
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The force required to deflect a cantilevered beam a distance X will be given by the formula 3EIX/L^3, where:
- E is the material's modulus of elasticity, which describes the degree to which a material will deform under load.
- I is the beam's cross sectional moment of inertia, which is the inertial resistance to rotation generated by the beam's shape, and in this case, accounts for the bending resistance inherit to the profile of the beam
- L is the distance between the rigid support and the application of load.
Quote:
Originally Posted by TheModMaster8
I accept you challenge.
you may be correct in the pressure needed to distort the metal (I don't have SolidWorks on this computer so i can't check) though this is when the metal is still in it's flatted form, my Dad is a civil engineer and I've asked him on shapes that would bare loads of weight, if you ever see a 'I' beam holding up a floor or roof you can see that vary little metal is required to hold a lot of weight, this is due to the form it had ( |-| ) <-- shape of an I-Beam) The flat side of this beam give the middle layer it's required strange as it distributes the force being applied to it, the same goes for sheetmetal,
if i have my flat piece of metal and apply said amount of force what i would get would be a traditional bend, how ever if i took that flat piece of metal and Bent bother sides so that it was making an ( [ ) form, and now tried to bend it with the same amount of force, you would see that the metal would no longer bend due to the extra support given off by the two linear walls, this is why support beams are in shapes of U's, I's, T's and L's, also triangles (but thats a completely different level of supports)
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This same basic principle also applies to extrusions. Extruded frames also give the advantage of making an even more structurally sound shape, the rectangular box, available in a more weight-efficient manner than sheet metal does, in addition to being made from much stronger material as Austin mentioned. In a pure race to achieve a target strength with minimum weight and optimal design, extrusion will win on paper every time.
Now, whether or not this is race to the top is in fact advisable, practical, or even desirable for your robot and team is a whole other matter. Resource sets, integration with the rest of the robot, ability to work the fabrication process into a build season, factors of safety and how far you want to go with them on the most important robot subsystem, ease of sourcing appropriate materials, and so on are all valid considerations, much moreso than squeezing the last couple tenths of pounds out of the drivetrain. My team does sheet metal drives and plans to continue to do so for a number of reasons, but pursuit of absolutely optimal strength/weight ratio is not of of them. I'm sure 971 has similar reasons. If you want to learn more about the complex ways in which sheet metal parts can interact to add strength to a chassis, I suggest checking out some of
971's drive bases. Some very impressive work.