04-02-2014 11:24

notmattlythgoe

Re: pic: 1648 Painted Frame / teaser 2

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.

04-02-2014 11:47

Anupam Goli

Re: pic: 1648 Painted Frame / teaser 2

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.

04-02-2014 11:53

notmattlythgoe

Re: pic: 1648 Painted Frame / teaser 2

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.

04-02-2014 12:33

apalrd

Re: pic: 1648 Painted Frame / teaser 2

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.

04-02-2014 12:42

notmattlythgoe

Re: pic: 1648 Painted Frame / teaser 2

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

04-02-2014 12:49

apalrd

Re: pic: 1648 Painted Frame / teaser 2

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.

04-02-2014 12:58

Anupam Goli

Re: pic: 1648 Painted Frame / teaser 2

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

04-02-2014 13:01

notmattlythgoe

Re: pic: 1648 Painted Frame / teaser 2

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

04-02-2014 14:34

apalrd

Re: pic: 1648 Painted Frame / teaser 2

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.

04-02-2014 14:47

notmattlythgoe

Re: pic: 1648 Painted Frame / teaser 2

Cool, thanks for the info.