Scrambler B

[Dark Sabre]

Courtesy of the judging staff from that year, we have quite a number of hires images from the 2006 national scrambler comp in the Image Gallery!

[cryjea]

What kind of launcher are you using cryjea? Different launchers have different speeds.

I'm using pulley launcher. I'm using 2by4s on the launcher. but my partner is redoing the car with balsa.

[croman74]

What kind of launcher are you using cryjea? Different launchers have different speeds.

I'm using pulley launcher. I'm using 2by4s on the launcher. but my partner is redoing the car with balsa.

Making the vehicle lighter is a good way to get the car to go faster. I don't know how balsa will do, but go ahead and try it. If that doesn't work, use basswood. It's a little heavier than balsa but is sturdier. Let me know how it does.

[Flavorflav]

Reducing friction is usually much more important than reducing weight, unless your car is really heavy. If you can't get bearings, use bushings and grease everything up with lubricant - not WD-40, something that lasts like silicone lubricant or bike chain oil.

[starpug]

Reducing friction is usually much more important than reducing weight, unless your car is really heavy. If you can't get bearings, use bushings and grease everything up with lubricant - not WD-40, something that lasts like silicone lubricant or bike chain oil.

I've had experiance with silicone lubricant in Trajectory, we used it to lubricate our pvc pipe that we shot the ball through. We had to lubricate the barrel every 10 shots or so, I don't know if this was the lubricant we used or if it was the way we used it but we couldn't get consistant results unless we did this. We got first so this wasn't a promblem really just annoying. Just a warning I think that the silicone lubricant might not have worn off but instead wiped off, I think you should keep in mind to check to make sure any lubricant is well applied after 10 or so tests so you don't lose consistency because the lubricant has worn off and you have more friction.

[jweil_buddha]

I've been doing scrambler for 2 years and this year am using the pendulum system again.
I made my car from balsa wood and it takes no stress from impact.
This is because I have a elastic band on the back of my car making a smoother contact and further push without any stress on the car at all.
This works well if trying to achieve lightness.


North Park Elementary

[captbilly]

It doesn't have to be incredibly sturdy for a pulley launcher. For a pulley launcher you want the scrambler to be more light weight than it is sturdy, that way you can get faster speeds.

We calculated the theretical top speed of a scrambler using a perfect frictionless pully launcher and the results may be a bit surprising to some of you. Though the mass of the vehicle enters into the equation it turns out to be almost insignificant once the mass of the vehicle drops significantly below the mass of the "falling mass". If your vehicle is at 150 grams then its absolute maximum speed would only go up by a couple of a percent if the vehicle mass was reduced by 90%, to 15 grams. Very few scramblers weigh as much as 150 grams, and 15 grams is impossibly low (the egg weighs several times that) so the range of speeds on a perfectly designed pully type launcher is very small. On the other hand this is the type of launcher that most of the top teams used. I suppose the pully launcher combines relatively easy construction with relatively fast times, but if you want a speed that is much higher than the crowd you will have to do something else.

The problem with the pully type launcher ends up being essentially the same problem that pully type trebuchets have, which is they aren't able to use much of the potential energy available in the falling mass. I won't say what the solution is, but think about the reasons why a FAT (free arm trebuchet) worked much better than a simple pully type and you should be able to come up with an answer. We were able to get travel times of about 2 seconds (10 meters), which is not possible with a simple pully type launcher. On the other hand at those speeds it became nearly impossible to stop the scrambler at a predictable distance. We ended up purposely using a heavier scambler and doing some other mods to slow the scrambler down, but our times were still just over 3 seconds. I just wanted to add that increasing the falling mass significantly beyond the mass of the scambler also has relatively little effect on top speed. What is happening is that most of the potential energy of the "falling mass" is simply converted into kinetic energy in the "falling mass", rather than being transfered to the scrambler.

[Flavorflav]

It doesn't have to be incredibly sturdy for a pulley launcher. For a pulley launcher you want the scrambler to be more light weight than it is sturdy, that way you can get faster speeds.

We calculated the theretical top speed of a scrambler using a perfect frictionless pully launcher and the results may be a bit surprising to some of you. Though the mass of the vehicle enters into the equation it turns out to be almost insignificant once the mass of the vehicle drops significantly below the mass of the "falling mass". If your vehicle is at 150 grams then its absolute maximum speed would only go up by a couple of a percent if the vehicle mass was reduced by 90%, to 15 grams. Very few scramblers weigh as much as 150 grams, and 15 grams is impossibly low (the egg weighs several times that) so the range of speeds on a perfectly designed pully type launcher is very small. On the other hand this is the type of launcher that most of the top teams used. I suppose the pully launcher combines relatively easy construction with relatively fast times, but if you want a speed that is much higher than the crowd you will have to do something else.

The problem with the pully type launcher ends up being essentially the same problem that pully type trebuchets have, which is they aren't able to use much of the potential energy available in the falling mass. I won't say what the solution is, but think about the reasons why a FAT (free arm trebuchet) worked much better than a simple pully type and you should be able to come up with an answer. We were able to get travel times of about 2 seconds (10 meters), which is not possible with a simple pully type launcher. On the other hand at those speeds it became nearly impossible to stop the scrambler at a predictable distance. We ended up purposely using a heavier scambler and doing some other mods to slow the scrambler down, but our times were still just over 3 seconds. I just wanted to add that increasing the falling mass significantly beyond the mass of the scambler also has relatively little effect on top speed. What is happening is that most of the potential energy of the "falling mass" is simply converted into kinetic energy in the "falling mass", rather than being transfered to the scrambler.

The last time scrambler was in C Division the mass of the car for a standard frictionless pulley launcher was irrelevant as long as it was under 500g, if I recall correctly. The limiting factor is velocity, not energy. The car cannot go faster than the mass, whose speed is fixed by the height of the drop unless you do something fancy.

[captbilly]

That is exactly correct. There is no magic number below which the mass of the vehicle becomes totally irrelevent but as the mass of the scrambler becomes a smaller and smaller part of the total mass of the vehicle / falling mass system, decreasing the mass of the vehicle become less and less important. To get speeds significantly higher than those of a simple falling mass you need to think of another way to harvest the energy of the falling mass. But as I said befor, you may find that beyond a certain speed stopping close to the barrier becomes a nearly impossible task. You have to weigh the speed vs distance to the barrier portions of the score and try and figure out where you can get more points. If going 5 meters per second gets you a really low time score (4) but causes your distance score to go up to 10cm (10), when you could reliably get 2cm at 2 meters per second then you didn't really get anywhere.

[croman74]

That is exactly correct. There is no magic number below which the mass of the vehicle becomes totally irrelevent but as the mass of the scrambler becomes a smaller and smaller part of the total mass of the vehicle / falling mass system, decreasing the mass of the vehicle become less and less important. To get speeds significantly higher than those of a simple falling mass you need to think of another way to harvest the energy of the falling mass. But as I said befor, you may find that beyond a certain speed stopping close to the barrier becomes a nearly impossible task. You have to weigh the speed vs distance to the barrier portions of the score and try and figure out where you can get more points. If going 5 meters per second gets you a really low time score (4) but causes your distance score to go up to 10cm (10), when you could reliably get 2cm at 2 meters per second then you didn't really get anywhere.

I never really looked at it that way. I guess that's a good point. If you can go fast and stop quite a ways from the barrier, it's basically the same as going medium speed and stopping right next to the barrier.