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Hayate wrote: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" .

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.

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.

spongeb0b wrote: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.

bernard wrote:

spongeb0b wrote: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.

One way to think of it: in the scenario described above, what would happen if the trigger was activated manually, without releasing the falling mass? If there's any force on the car, it's no good. All the propulsion (100% - even 99 is no good) needs to come from the falling mass. Any tension on the spring before the mass is released is "extra" energy that's not allowed.

SPP SciO wrote:One way to think of it: in the scenario described above, what would happen if the trigger was activated manually, without releasing the falling mass? If there's any force on the car, it's no good. All the propulsion (100% - even 99 is no good) needs to come from the falling mass. Any tension on the spring before the mass is released is "extra" energy that's not allowed.

I'm having a hard time imagining how this device would work. These discussions are so much better in person or with illustrations Anyway if the trigger was activated without releasing the falling mass then the vehicle would in my mind be powered not by a falling mass but entirely by the person pulling on the spring and locking it in just like a sling shot. There would be no need for a falling mass in such a device. In my example 100% of the vehicle is powered by the falling mass. It is just that I am allowing the mass to fall 1% first then I prevent the mass from falling further, when released, the mass is then allowed to drop the rest of the 99% of the way. All the energy that is used to stretch the spring is coming from the falling mass.

spongeb0b wrote:

SPP SciO wrote:One way to think of it: in the scenario described above, what would happen if the trigger was activated manually, without releasing the falling mass? If there's any force on the car, it's no good. All the propulsion (100% - even 99 is no good) needs to come from the falling mass. Any tension on the spring before the mass is released is "extra" energy that's not allowed.

I'm having a hard time imagining how this device would work. These discussions are so much better in person or with illustrations Anyway if the trigger was activated without releasing the falling mass then the vehicle would in my mind be powered not by a falling mass but entirely by the person pulling on the spring and locking it in just like a sling shot. There would be no need for a falling mass in such a device. In my example 100% of the vehicle is powered by the falling mass. It is just that I am allowing the mass to fall 1% first then I prevent the mass from falling further, when released, the mass is then allowed to drop the rest of the 99% of the way. All the energy that is used to stretch the spring is coming from the falling mass.

The limiting factors are the total mass (2kg) and max height (90cm). I hear what you're saying - by lowering your mass a bit, you put the spring under minimal tension, just to keep the strings taut - I'm inferring this helps you get a straight launch. But, in the ready-to-launch position, the car can't be preloaded. I'd suggest raising your mass a little higher, leaving your string a little looser, and you would be in compliance without sacrificing too much. There are lots of effective techniques for a smooth release.

Better advice: don't take my word for it. I'm just a coach - you should ask yours!

Our first run had a violation for going out of the track area, but it still stopped close to the wall, just the wall for the other team (two teams at a time). Our second run was accidental launch, but they ended up taking both I think? Are they only supposed to take the higher scored one?

cemsc10 wrote:Our first run had a violation for going out of the track area, but it still stopped close to the wall, just the wall for the other team (two teams at a time). Our second run was accidental launch, but they ended up taking both I think? Are they only supposed to take the higher scored one?

They will take the higher scored launch. They may not have been able to score your second run, so you may end up with a comp violation.