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Originally Posted by DampRobot
Very cool. It'SS an amaSSing SShaker RoboticSS robot as uSSual!
Can you talk a little bit more about your arm gearbox? What happened at WPI, and how do you mean it's repairable in place?
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Sh1ne touched on most of it, and I was mostly focused on DT / gripper, but I can expand on this. The blue gearbox side plate comes off with a few bolts at which point you have access to all of the gears and shafts without removing the gearbox from the robot. Ideally the robot is tilted on its side for this.
One of the challenges of a geared arm that relies on Vex gears is the compounding effect of slop on the system. Vex gears are broached bigger than .500, and thus they have a bit of play on the shaft. Vex shafts are undersized to fit bearings. Multiply this by a dozen gears, and factor in the .003 center add, and you have a lot of slop once you get to the arm.
Our dampening system (a gas spring pulling the arm toward the ground) takes up this slop and smooths out the arm motion at key points of travel. The spring also serves a secondary purpose - in the event of gear failure, the arm is pulled toward the ground. This lets us manipulate the game piece for the rest of the match.
I really wish that the hex broaches on Vex gears were tighter, but I understand the desire to fit them to any hex shaft. We'll have to investigate ways to make geared arms with less inherent slop in the future. The geared single joint arm is quickly becoming a "signature" of 2791 mechanical design, so further iterations of this concept will likely find their way to future robots. That, or we'll finally listen to Foss and use cylinders.
Does this mean it's too late to ask for a flux capacitor? - Peter Matteson [more] 
26-02-2014, 13:35
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