Many missions often involve grabbing, pushing, moving or placing various objects. According to the specific mission, you can get creative and think of various combinations of L-shaped or angled beams, with partly moveable elements, held in position by rubber strings or by gravity.
In this article, we will discuss claw-based attachments.
One example was the 2020-2021 season mission where a fairly heavy wheel was laying on the ground and it had to be pulled a few inches (or centimeters). It was not easy to make sure we always arrived at exactly the same spot, to “grab” the wheel. Since the wheel had spokes, we came up with the idea of using several long pins, just “hanging in there”, on the front part of our left arm.
When the arm was lowered, one or more of these pins would always end up grabbing some part of the wheel, so the robot would just go back with the arm lowered, and, once in the right position, simply lift the arm, to free itself from the wheel, which would remain in its final position.
Such mechanisms in general aid with grabbing oddly shaped elements and bringing them to precise positions.
Another mission required flipping a large tire. So we attached a grabbing arm made of angle beams and bare pegs to one of the up-and-down rack-and-pinion mechanisms, and had the robot lift and drive forward at the same time.
The pegs in this case brought the tire to an upright position (precise) and then kept pushing to make it flip completely (also precise).
The red rubber bands help maintain the grabber horizontal, because its part made of angle beams can turn a bit, to allow for more flexibility: the diameter of the wheel is larger than what the whole rack-and-pinion can travel, so at the very top of the flipping movement, when the wheel is vertical, right before falling on the other side, the robot would otherwise get stuck. The freedom to turn of the grabbing part allows it to “go over the wheel” while keeping “hold of it”, to complete the flipping motion.
© The RoboMentors (Marc and Anne)