Scrambler B

[Hayate]

Hey guys, I just have a quick question. I have a spring launcher, it works fine and all but I just want some clarification. The spring we are using is being pulled on even before we release the mass - car has tension on it before launching - is this illegal? If it is we can just change it, but it would be slower.

[bernard]

Hey guys, I just have a quick question. I have a spring launcher, it works fine and all but I just want some clarification. The spring we are using is being pulled on even before we release the mass - car has tension on it before launching - is this illegal? If it is we can just change it, but it would be slower.

Yes, your spring should start without any tension; see rule 2.c. Potential energy stored in the spring is propelling your vehicle, so it is currently faster.

[SPP SciO]

Hey guys, I just have a quick question. I have a spring launcher, it works fine and all but I just want some clarification. The spring we are using is being pulled on even before we release the mass - car has tension on it before launching - is this illegal? If it is we can just change it, but it would be slower.

That's probably not going to work. It was explained to me by Bro. Nigel, whom I believe is a national level supervisor, that there needs to be slack in the string/spring before the mass drops. If you lengthen the string just enough to where it's not taut before launch, you're good.

Also, since the spring will be pulled upward, it's mass will count toward overall potential energy and will need to be included in the sub-2kg total.

[bernard]

Also, since the spring will be pulled upward, it's mass will count toward overall potential energy and will need to be included in the sub-2kg total.

This doesn't seem correct; if your have your spring launcher setup like the one pictured in the Scrambler Wiki, part of the spring increases in potential energy. Perhaps I'm missing something here?

[Hayate]

Okay thanks. I never heard about the spring being part of the mass before. Yeah I guess the spring is rising but the rules say any part that decreases in gravitational potential energy is part of mass so wouldn't the spring technically be increasing in that?

[InfiniCuber]

Okay thanks. I never heard about the spring being part of the mass before. Yeah I guess the spring is rising but the rules say any part that decreases in gravitational potential energy is part of mass so wouldn't the spring technically be increasing in that?

Yeah this is rather interesting. I'm not sure if there is something particularly different from last year's rules, but at nationals last year, they didn't make me (or anyone else I saw) have their spring/elastic massed and added to the 2kg limit. It was usually deemed "negligible" .

[SPP SciO]

It's quite possible I was wrong about that initially - and the animation on the wiki does show how the spring is pulled upwards, but it doesn't fall back down before the car is released. In the spirit of "better safe than sorry" we are going to take that possibility into account though.

[spongeb0b]

The weight of the spring itself will be adding tension on the string. I feel that this is a very hard thing to judge since you do not really want the string to be too loose. Further, the energy potential of the scrambler is depended on the weight of the falling mass. The fact that you are "pre-loading" the device by pulling a little on the spring does not add any more energy to the setup.

[bernard]

The weight of the spring itself will be adding tension on the string. I feel that this is a very hard thing to judge since you do not really want the string to be too loose. Further, the energy potential of the scrambler is depended on the weight of the falling mass. The fact that you are "pre-loading" the device by pulling a little on the spring does not add any more energy to the setup.

The stretch due to weight of the spring will likely be negligible. And pre-loading the spring can add significant amounts of energy to the setup; think about how your mass stretches the spring as it falls.

[spongeb0b]

The weight of the spring itself will be adding tension on the string. I feel that this is a very hard thing to judge since you do not really want the string to be too loose. Further, the energy potential of the scrambler is depended on the weight of the falling mass. The fact that you are "pre-loading" the device by pulling a little on the spring does not add any more energy to the setup.

The stretch due to weight of the spring will likely be negligible. And pre-loading the spring can add significant amounts of energy to the setup; think about how your mass stretches the spring as it falls.

Assuming the launcher is the type where the falling mass triggers the release mechanism at the end of the fall, pre-loading the spring, i.e. letting the mass fall say an inch then locking it in, should not add any more energy when the vehicle is eventually released when the mass hits its travel end and releases the vehicle. Let's put it another way, say we do not pre-load the spring, when the mass is release it falls 50cm before releasing the vehicle, the spring is stretched exactly 50cm as well. Now if we pre-load the spring by letting the mass fall 1.0 cm pulling the spring slightly exactly 1.0 cm as well. We we release the mass it falls exactly 49 cm before releasing the vehicle. In this case the spring is also stretched exactly 50cm, thus equal amount of energy is expended. Maybe I am missing something in my logic.