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Unread 24-03-2010, 17:25
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Re: Engineering Challenge- Spring Loaded Kicker Edition

Quote:
Originally Posted by ICanCountTo19 View Post
B. Less springs

More stroke -> more time for the mass to accelerate -> more momentum at impact -> farther shot
You're making an important assumption about the design of the kicker here, which may not be true. If the kicker is set up like a big pendulum, with significant mass and significant travel time before contacting the ball, then I think you're correct.

What if that's not the case? What if your kicker is designed to work without significant mass and without any travel time before contacting the ball? In other words, you have a relatively mass-less kicker already in contact with the ball when you start to accelerate it. That's essentially our design, and it works great (clears 1 bump easily, scores very well). Think of a slingshot, and you'll have a good idea of how the physics of it works.


Now, everyone should keep in mind that a robot cannot create energy. The form of the energy can change, but it can't be created.

In this situation, a motor is able to exert a certain amount of torque (which can be translated into a linear force very easily) before it stalls. In short, this means it can pull back the kicker a distance x such that the linear force the motor is outputting is equal to kx. The stall torque for any given motor is a constant.

So, what do we do with k? Well, if we increase k, we get a shorter draw but the same amount of force. If we decrease k, we get a longer draw, but the same amount of force. In the end, the force (remember F=ma?) remains the same (as does mass and acceleration). The only thing we change is the draw.

So, does increased draw help in this situation? Well, that all depends on the design of the kicker


We ran into this problem early in the season. With our design, increasing the draw really doesn't get you anything. Adding a second motor and more springs, however...