Gravity Vehicle C

[Frogger4907]

Okay, another question, relating to the rules. It says that the release mechanism must be a pencil (line 3.h), but it does not state unlike last year's mousetrap rules that the pencil must be used in a vertical manner. So based on that line of the rules, I can use the pencil to pull out a release mechanism right? I just want to confirm it. And I know this isn't the place for official clarifications, these are solely opinions, etc.

Thats what we've been doing.

[questionguy]

What are some good materials to make a ramp out of? I was thinking of making a curved ramp over a flat ramp for obvious reasons but creating a ramp out of a bendable material is the tricky part. Would aluminum channels glued onto a wooden base be efficient?

Read the wiki, it should give you some other ideas to build a ramp. Aluminum channels might be difficult in maintaining the same curve for each channel

[Balsa Man]

I was thinking of making a curved ramp over a flat ramp for obvious reasons...

I'm curious, given the extensive discussion on this topic, what you think those obvious reasons are
?

[themadhatter]

I was thinking of making a curved ramp over a flat ramp for obvious reasons...

I'm curious, given the extensive discussion on this topic, what you think those obvious reasons are
?

I believe elmono means that the vehicle will travel faster down a brachistochrone curve than a flat ramp. The problem with that idea is finding an inexpensive material to use for it.

[Balsa Man]

I was thinking of making a curved ramp over a flat ramp for obvious reasons...

I'm curious, given the extensive discussion on this topic, what you think those obvious reasons are
?

I believe elmono means that the vehicle will travel faster down a brachistochrone curve than a flat ramp. The problem with that idea is finding an inexpensive material to use for it.

That's what I figured elmono meant, and why I asked. The current end-point of the discussion is that a b-curve ramp will not get you a measurable/meaningful improvement in horizontal velocity - which is what will drive your time score. Building a b-curve ramp will take significantly more time/effort, for essentially no payoff. Material expense is not an issue - thin aluminum sheet, plexi, plywood, even poster board, on a set of ribs will work fine to do it. But there is no reason to build one.

[chalker7]

That's what I figured elmono meant, and why I asked. The current end-point of the discussion is that a b-curve ramp will not get you a measurable/meaningful improvement in horizontal velocity - which is what will drive your time score. Building a b-curve ramp will take significantly more time/effort, for essentially no payoff. Material expense is not an issue - thin aluminum sheet, plexi, plywood, even poster board, on a set of ribs will work fine to do it. But there is no reason to build one.

I agree that this is probably what elmono meant, and that a brachistochrone curve will not give any meaningful improvement to final time, however I think that to many of the people on this board, brachistochrone has become shorthand for "curved." For anyone who has not read through the old posts, brachistochrone is just a specific type of curve, not all curves. Mathematically, it might be the best, but is probably not necessary. However a simple, gradual curve will give significant benefits (specifically in reducing the impact when the vehicle hits the floor) and is almost certainly worth the extra effort in construction. I'd use thin sheet metal or thin particle board screwed down to a rigid wooden frame to put it together.

[Balsa Man]

I think we're pretty much on the same page.
Yes, there absolutely needs to be a smooth (as in curved) transition to the floor; and the minimum radius of that curve needs to be significantly larger than the radius of the wheels. Whether that's done with a contunuous curve from the top, or a flat upper section and curved lower section; not a lot of difference in construction time/ease. To actually plot up a real brachistochrone curve that fits the constraining dimensions, and provides a sufficiently large radius of curvature at the bottom to avoid a "slamming" transition, and then to translate that curve accurately to bracing (whether ribs or another bracing structure) is a significantly bigger challenge - that there's no reason to take on.

[themadhatter]

I understand that some of the gravitational PE will be converted to rotational KE. What I'm not sure about is how to calculate rotational KE when you have multiple wheels of varying shapes and sizes.

[Frogger4907]

I think we're pretty much on the same page.
Yes, there absolutely needs to be a smooth (as in curved) transition to the floor; and the minimum radius of that curve needs to be significantly larger than the radius of the wheels. Whether that's done with a contunuous curve from the top, or a flat upper section and curved lower section; not a lot of difference in construction time/ease. To actually plot up a real brachistochrone curve that fits the constraining dimensions, and provides a sufficiently large radius of curvature at the bottom to avoid a "slamming" transition, and then to translate that curve accurately to bracing (whether ribs or another bracing structure) is a significantly bigger challenge - that there's no reason to take on.

Whats the reason to not do it? Why not?

That's what I figured elmono meant, and why I asked. The current end-point of the discussion is that a b-curve ramp will not get you a measurable/meaningful improvement in horizontal velocity - which is what will drive your time score. Building a b-curve ramp will take significantly more time/effort, for essentially no payoff. Material expense is not an issue - thin aluminum sheet, plexi, plywood, even poster board, on a set of ribs will work fine to do it. But there is no reason to build one.

Where is your evidence of essentially no payoff? Have you run tests? We can't just assume...

[illusionist]

Frogger, have you been following the lengthy discussions that occurred on the last few pages...?

The reason not to do it is simply for simplicity and ease of building. If you really want to go plot out a b-curve and make it work, then go ahead.

BalsaMan has run tests using scale ramps, so his conclusion is valid. Also, just using an equation will tell you that it does not make a significant payoff. The amount of horizontal v that the vehicle has is based on how far the center of mass of the vehicle has to fall. In our case, it will be the same for all ramps. The biggest design element of the ramp that you have to concentrate on is ensuring that you have a smooth transition. No one is assuming anything.