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Originally Posted by KenWittlief
Since you only care about the end positions, all you need is a piston and a lever. The piston does not need to go to its stops, put mechanical stops on the lever that can be adjusted to set the alignment for each wheel.
if fact, it could be spring loaded in one direction, so the robot will default to one direction if your pnuematics fail (or simplify your pnuematics so they are only driven in one direction.
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The more I think about it and get frustrated, the more I think this will be my only option. What I'm worried about is in the retracted position, your piston should end up directly in line with both the lever arm and the pivot, and when you try to extend, the piston will jam. However, with some tension springs you could alleviate this by pulling perpendicularly to the piston, so that when it extended, it would be drawn over. I just wanted a nice, smooth linkage that would afford me a one mechanism, no-worry solution, but I'm beginning to think it can't be done easily.
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Originally Posted by cromat44
I think you're trying to make what is known as a crab (aka swerve) drive. There are many post / half completed designs you could find.
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Well, it's more of a variation on the crab/swerve. The problem with crab/swerve drives is that because of their go-anywhere design, they require that their modules be turned by motors. This results in, generally speaking, a slow direction change, and long lengths of chain/ belt, or an elaborate gearbox- linkage mechanism.
The advantage of simply choosing two module angles is twofold. First of all, you can more easily achieve near instantaneous direction change. (i.e push against a robot, and in 1 second be ten feet away sideways). Secondly, pnuematics in this circumstance offer a nice reliability factor. They are light, easily mounted, offer simple changeout, and if you jam a module somehow, they won't burn up trying to move that single module.
Another benefit to this design is that you may stray away from traditional crab construction, which subject the bottom of the module to high levered loads. They are normally supported only by a teflon ring at the bottom of the module. If you only try to move the module 90 degrees however, you can move the pivot from the top of the module to the side, sort of like a heavy duty door hinge.
In this way, you may make the hinge as beefy as you like to support the robot's weight loads, while the hinge's structure can more easily withstand horizontal impulses, the type most likely to see during a match.