Hexabot: Build a heavy duty six-legged robot!

Step 5Weld the frame

Weld the frame
Unfortunately, I did not take pictures of the process I went through to weld the frame, so there are only photos of the finished product. Welding itself is a topic to deep for this Instructable, so I won't get into the gritty details here. I MIG welded everything and used a grinder to smooth out the welds.

The frame uses all of the steel pieces cut in Step 3 except for the Legs and Leg linkages. You may notice that there's a few extra pieces of metal in my frame, but these are not critical structural components. They were added when I already had most of the robot assembled and decided to add some additional components.

When welding the frame, weld every joint. Anywhere that two different pieces of metal are touching, there should be a weld bead, even where the edge of a piece of tubing meets the wall of another. The gait of this robot subjects the frame to a lot of torsional stresses, so the frame needs to be as rigid as possible. Welding every joint completely will accomplish this.

You may notice that the two cross members in the middle are slightly out of position. I measured from the wrong side of the tubing when initially laying out the bottom half of the frame for welding, so the positions of those two cross members are off by 1 inch. Fortunately, this has little effect on the rigidity of the frame, so I wasn't compelled to remake the entire thing.

The pdf files presented here are drawings with dimensions to show the position of components in the frame. These files are also present in the folder with the CAD files in Step 1.
sideview.PDF(792x612) 45 KB
topview.PDF(792x612) 45 KB
robotframe.PDF(792x612) 54 KB
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3 comments
Apr 21, 2009. 5:23 AMDon.Jambo says:
a new issue has come up: the wall thickness of the rectangular tube. I went this weekend to buy the "iron" needed, and I told the guy there that i want a the 1in by 1in tube for a frame, and that I will weld it together, and the guy told me that it's better to use the rectangular tube with 0.078" wall (2mm), not the 0.065" wall (1.65mm). after you welded the frame and used the robot for a while, did the rectangular tube have any cracks in the area where you welded? The the store the 19.6ft, 0.065" wall tubes seemed very flexible, not that robust as the 0.078" wall. last thing would be the weight of your frame. did you get to weigh it? If between the 0.078" wall frame and the 0.065" wall frame is a very big difference, I'll stick also with the 0.065" wall. Please post!
Apr 24, 2009. 4:21 AMDon.Jambo says:
Could you please weigh or approximate the weight of the frame?!
Apr 14, 2009. 3:15 AMDon.Jambo says:
If I use 1.18" (3cm) square steel tubing in stead of 1" (2.5cm), and 2.36" (6cm) x 1.18" in stead of 2" x 1" with same wall thickness that you used will it make the frame a lot more robust, but too heavy?? Is it worth it?

Or it's ok to go with 1" and 2" x 1"? I don't know how robust your frame is. If it's good enough I won't go with thicker square tubing (it's the same wall thickness).

please reply, and also specify if I might mess up the power-to-weight ratio!
Thanks


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Author:rpantaleo
Mechanical Engineer