pic: 1648 Painted Frame / teaser 2



Painted competition frame. We decided to use the same colors, but a different scheme from last years. Instead of doing Red structural/Black functional, we decided to go all Black with Red highlights.

Very nice, is there any reason that you don’t just drill through the 80-20 for the cross braces to get rid of those angle brackets? Could cut down on some weight.

The angle brackets allow us to easily modify the position of the crosspieces if needed, and the gussets allow for a more rigid structure and evenly distributed load.

Sounds good. We usually use the Anchor Fasteners for the 3 piece corners when we’ve built our chassis out of 80-20. What are those corner pieces that you have used? There is a major misconception that 80-20 is heavy, but if built right it can be very light. Well done.

80-20 is heavier per length than comparable strength box tubing. It’s not a misconception. Due to the profile it’s also less stiff in some dimensions (especially torsion of the bar).

If you can get the weight out elsewhere (through use of lighter joints or other fabrication methods as a result of the 80-20 profile), then it might be lighter. But, thinwall box tubing with bolted/rivited gussets (vexpro style) is definitely lighter than the same thing made of 80-20.

I’m curious what the weight of OP’s chassis as painted is.

1x1 tubing with 1/8 walls is actually the same weight per foot as 80-20.

1/8" wall would be stiffer in the directions we are concerned with in a chassis design like this.

Decreasing the wall thickness to match the equivant 80-20 stiffness, it would be lighter.

We haven’t weighed the frame yet, but according to inventor, we’re looking at about 15 pounds without paint.

Would you mind pointing me to the data that backs this up?

I was curious too, so I ran some simulation (using Inventor’s FEA tools) and found that 8020 is in fact significantly weaker in torsion and slightly weaker in bending. I can’t attach images to a CD-media, so I’ll summarize the results:

For bending, I constrained both ends of a 1’ beam and applied a load to the top face. For torsion, I constrained one end of the same beam and applied a torque to the other.

100lbf load on top face of section, ends constrained:
0.001536" max deflection 8020 (load split between two top flanges on either side of groove)
0.001614" max deflection 0.063"
0.001006" max deflection 0.125"

200 in-lbf torque at end of section, other end constrained:
0.1311" max deflection 8020
0.01055" max deflection 0.063"
0.006772" max deflection 0.125"

The weight of 8020 vs 0.125" 1x1 box is virtually the same, 0.063" would be roughly half.

Cool, thanks for the info.