Articulating tubes on roller claws

[EricH]

Originally Posted by Chris is me

You're probably definitely going to need 2 motors to articulate a tube.

I think it could be done with one. It wouldn't be the most elegant solution, or the lightest, but I think it could be done.

What I'm thinking is something like a dog shifter, with a "forward" mode, a "reverse" mode with a second gear to reverse the belt, and a "neutral" mode (in between forward and reverse) for slower articulation. Alternatively, you could just have the "neutral" mode.

Now, if you want to count any servos used as motors, then yeah, that is 2 motors.

[s_forbes]

Originally Posted by PAR_WIG1350

...By locking the differential case in place, the rollers spin in opposite directions rotating the tube within the claw, by locking the two outputs together, the rollers spin in the same direction to intake or release the tube...

Originally Posted by EricH

Now, if you want to count any servos used as motors, then yeah, that is 2 motors.

It sounds like a much more fun challenge if you limit the mechanism to using only one degree of actuation! I can think of a few approaches, but they all inevitably end up using more hardware than simply hooking up two motors to drive the rollers.

This was a good lesson we took from last year; if you minimize the degrees of freedom of a manipulator you can make a system that is in theory simpler than one that uses more actuators, but the final result typically ends up being more complicated than simply using multiple motors. Still, that won't stop us from trying... manipulators that utilize minimal actuators have a nice appeal.

[Peter Matteson]

The lightest simplest design is to use 2 motors in this case. Adding a linkage or switching system adds complexity and failure points. This is a case of bad engineering practice. Remember just because you can make something doesn't mean you should. Complex mechanisms like that have been the downfall of more FRC robots than anything else over the years.

[Jared Russell]

If you want to arbitrarily orient the tube, then two motors is the simplest option.

But I would argue that there is not a lot of value in being able to arbitrarily rotate the tube, in and of itself. Typically, there is one orientation you want those tubes to be in when you go to score. So being able to rotate the tube is only useful in that you can bring any tube you pick up or are carrying to that orientation.

If getting the tube you picked up into your desired scoring orientation is your goal, there are several one-motor ways to make it happen. You can design your roller claw such that the geometry forces tubes to be sucked in to the correct orientation.

[thefro526]

340's roller claw this year oriented tubes pretty consistently from what I saw at Chesapeake. They used one motor (I think) and a series of rollers to suck tubes in while also turning them to vertical. Here's a picture for reference: http://www.chiefdelphi.com/media/photos/36576