Most Difficult Strategy

[Denman]

I would say that the hardest thing to design was the ball lifter. We spent a week or so with many different designs and not getting anywhere, until we just decided to pick one and get on with it.

[Grommit]

In our team's experience this year, we found the challenge (design, execution) of lifting a 2x ball to be the greatest, for the following reasons:

1) We found it difficult to grip the ball tightly, mainly because we had used a design with only two arms to grab the ball, and poorly designed ones at that. The teams that managed to get away with two grabbers used either:
a- cups that clamped down with a large surface area
b- arms that contacted the ball along a long surface
Ours had neither, and worse, they clapped together when they opened and closed. What a mess.

2) We also found it difficult to lift the ball, perhaps due to our own incompetence, but also because of the weight of the ball.
The ball is 5lbs, and holding that at about 2 yards moment arm is a good 30 foot pounds of torque needed to lift the ball. This converts to roughly 50 (correct me if I'm wrong) newton meters, and remember that the Van Door provides in the area of 30-34 Nm of torque, depending on the direction it is turning. The window motor is even weaker, providing less than 6 Nm. Clearly, some amount of gearing is needed, and we used 4:1 sprocket ratio to acheive this. Sadly, we made the mistake of mounting the heavy motor on the moving part of the arm, as well as a heavy cylinder that was the wrong size anyways, and some other stuff we shouldn't have needed. End result: our arm had insufficient torque to lift the 5 lb ball past the 90 degree point without great strain.

3) We would tip over when we had our ball held out in front of us. This was not unexpected, but it still makes the job difficult.

Would you like to hear this story's happy ending? We offered the 2x ball grabber a quick and painless death at the hands of a hacksaw. It took just a minute and we lost about 25 pounds. In its place we built a hanging device.

Moral of the story: Go hang yourself.