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Unread 07-07-2008, 11:10
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Re: 6WD Chassis Stiffness vs. Maneuverability

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Originally Posted by kramarczyk View Post
I swear, that white paper is one of the best kept secrets out there. I did a spreadsheet to save some of the 4x4 users from the minutia of the math. http://www.chiefdelphi.com/media/papers/1917 I've got a beta version for 6x6, but got stuck on some of the issues we're discussing here.
This is a good spreadsheet, but it assumes the center of mass, center of area, and all forces of the wheels are perfectly coplanar and are at a height of zero. It also assumes the center of mass is right/left centered on the bot, which sometimes isn't the case. Also, for a 6WD rocking chassis to rock, the CoM must break the vertical plane of the middle axle, which inherently assumes a CoM above the axles.

Since the act of rocking helps a turn anyways, perhaps the first iteration of an improvement to the spreadsheet could simply be to account for a three-dimensional CoM? Even turning in place, a CoM that isn't centered will cause each wheel to contribute a different turning moment. Then we could split the 6WD rocking chassis into two separate 4x4 arrangements with different CoM heights based upon the "default" and "rocked" states.

Of course, early in the build season we would have to estimate CoM height based upon desired manipulators (elevators, arms, etc), but later in the season for tweaking it can really help determine the best placement for mount points and heavy-component placement.
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