Moment of inertia and turning performance

[IKE]

Originally Posted by Michael Corsetto

How is the kitbot frame's torsional stiffness? I don't have much experience with it.

Awesome thread, all this talk about frame flex has got me thinking!

-Mike

Kit bot=Noodle frame. It does have a fair amount of rock, so it works out well.
1114's Kitbot on Steroids improves this using the robust base-plate.

Super structure design can make a frame stiff.
Welding can make a frame stiffer.
Gussets can make a frame stiffer.
Additional rivets at attachment locations.
Gluing.
In general, Triangulation beats Boxification (I made the last one up).

There are lots of ways that can make a frame stiffer, but many do not without some attention to detail.

If you are doing a sheet metal chassis, making a "model" out of posterboard can be very helpful. The posterboard is much less stiff than metal, but the general weak spots should be the same locations.

If you like doing FEA, you can apply moments in opposite directionon the center of the outer rails. Moments on the order of 180 to 240 in*lbs is a good place to start. Look at the displacements relative towhere the wheels would be. Displacements on the order of 1/16th of an inch or more are important. If you think about the "pile" of the carpet. A light touch to fully supported (60-75 lbs) is on the order of 1/8".

If someone was interested in doing some testing, you could anchor 3 corners of a frame onto something rigid (say very stiff table or multiple pieces of plywood). You could then apply weight to the 3rd corner and measure displacement . Trying different gussets, bracket, welding... and repeating the experiement would make for a very nice paper and possibly a cool sciencefair project.