Quote:
Originally Posted by cxcad
This year I think 971 has built one of the most effective and innovative chassis, and consequently I want to emulate what they have done.
I noticed from the Flikr account that this year 971 departed from from what I presume the "original" three piece design. Could the octagonal shape not be achieved in three pieces? ( image here) |
We ran the "original" 3 piece design in 2012 and 2013, and it has served us very well.
We couldn't find a way to make an octagon with a 3 piece chassis, which means it probably isn't possible or easily to machine. We wanted an unbroken flange to help form a backbone to tie everything to and to tie everything together. The best way to do that that we found was to set the chassis up as you see this year. We started by figuring out where to put the wheels and pulleys, and then built the frame to hold everything in place. This resulted in the jog on the inner face, which resulted in an internal corner which couldn't be bent without breaking things up into more pieces. We also needed a parallel face to bolt the wheel tensioners to, which drove the inner frame rail shape that you see. You can see the set of 8 #6 holes that define the tensioner location in one of the pictures.
Quote:
Originally Posted by cxcad
That brings the questions: do the ribs provide significant rigidity?
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In theory, they should provide more torsional rigidity and prevent the tube from collapsing. We could probably leave them out, if we really wanted to, but I'm a fan of overkill when it doesn't hurt you... We also choose to bolt our superstructure down either to them, or right next to them, which spreads the load a lot better by spreading it through the rib.
Quote:
Originally Posted by cxcad
What's the advantage of one piece modules over the traditional railed approach? ( image [I know there are ribs inside it, but for the most part it is one piece?]) |
By railed, do you mean a classic WCD chassis? We have lots of sheet metal sponsors, and a large amount of experience working with sheet metal. We build robots that play to our strengths, and this chassis does. By building a big tube instead of 2 rails like the old AM chassis, we get a lot more structural rigidity. It is quite hard to flex one of our chassis. Our wheel tensioners are designed such that the act of tensioning the wheels locks the shaft into the frame, so it really isn't very hard to get the wheels out. The wider wheels and wider body tube lets us flip the CIMs over the wheels, which opens the belly pan up significantly.
Quote:
Originally Posted by cxcad
What is the advantage of PEM nuts, is there a closer image of them in use, how do they hold up to the beatings and vibration? ( image) |
PEM nuts give you the strength of steel threads in aluminum. When used properly, they are quite strong and have no problems. When used improperly, they fall out and are a pain to use. When using PEM nuts, make sure that you never let any load be put into them that would try to press them out of the material. On our drive base, we only used them to mount speed controllers to our belly pan. In our superstructure, we really only used them in a couple places to let us remove parts quickly.