Our team was considering a modified octagon design. We have not had any luck searching for pre-made 135 degree brackets. We do not know all of the suppliers - mainly look at AndyMark and google search. If there is any senior teams that know a possible supplier we would be happy to receive advice.
80-20 has a 6 hole 45 degree that should work. But it may be faster/cheaper to cut & drill aluminum plate.
Or cut the kit chasis down in size for the ‘rectangles’, and 1x1 aluminum square tube (available at Lowes & Home Depot) will fit inside the kit ‘C’ channel for the angles.
Are you looking to use the Kit chassis rails?
I think the Corner Connect’s in the kits can turn at such an angle, look at the omni kit chassis, it looks like they are turning at 45 degrees there. You could probably get it to work. You could always make a plate of aluminum to turn the corner, and put it on the top and bottom, attached with two bolts to each piece. You might need to face some of the angled pieces with the C facing out instead of in, to get the Corner Connects to work.
The set your own angle brackets here might work out: http://www.mcmaster.com/#catalog/116/2991/=5j274g
Thanks for the suggestions, we will take a look into them.