Gravity Vehicle C

[wlsguy]

What does it say? (don't have my rules, sorry)

"Teams design, build, and test one vehicle and ramp...."

Based on the description, ramps must be built by the students (to avoid violating the "Spirit of Competition").

[Primate]

For a point mass, velocity depends only upon the vertical drop, but that's not reason to eliminate the brachistochrone curve entirely. Scoring is still based on shortest time.

Taking rolling kinetic energy into account:






for a disk



Looks like minimizing the wheel mass to vehicle mass ratio is crucial, as well as decreasing the rolling resistance of the tires. (Of course, increasing the weight of the vehicle increases the rolling resistance...) I'm leaning towards a brachistochrone curve that flattens out at the end to maximize horizontal velocity. Balsa Man, I feel like the minimal gain in com vertical height by starting out flat will be canceled out by the extra time to get down the ramp, so long as you move the com back. Plus, 3b requires that all vehicles start non-horizontally, so you'd have to be somewhat non flat anyway.

Someone please yell if my calculations/conclusions are wrong.

I didn't see anything in the rules disallowing electric braking systems; anyone remember what people were using for EV?

Edit: lol, rule 3h made no sense the first time I read it: "Competitors must release the vehicle by using an unsharpened #2 pencil...to actuate the release mechanism. Competitors must not touch the release mechanism to start the run."

[illusionist]

As for the vehicle not being a point mass. Yup, that's a valid concern, but it really depends on the design of your vehicle. Of course, if your vehicle's short, the center of mass of the vehicle will follow the curve of the ramp pretty well. But now, imagine your vehicle to be as along as the ramp (connecting the top of the ramp to the bottom of the ramp), and you put all your mass at the back (higher) end of the vehicle. Assuming that the back wheels are pretty close to the back of the vehicle and that they aren't ginormous, the center of mass of your vehicle will still follow the curve of the ramp pretty closely. On the other hand, if you have a really long vehicle that once again connects the top of the ramp to the bottom of the ramp, depending on the ramp's curvature, the center of mass of your vehicle will most likely not follow too closely to the ramp's curvature.

Does that mean that there is no maximum length of the vehicle/wheel base? I know that there is maximum axle width of 35 cm.

[bearasauras]

I didn't see anything in the rules disallowing electric braking systems; anyone remember what people were using for EV?

I think rule 3k says something about not using electrical components on the vehicle, the ramp or any alignment devices.

*Standard disclaimer about this is not an official clarification, etc. If you want 'official' statements on this issue please submit a question to the soinc.org clarifications page.

[fishman100]

Does that mean that there is no maximum length of the vehicle/wheel base? I know that there is maximum axle width of 35 cm.

Rule 3d states that:

The vehicle's track (distance between outside surfaces of the left and right tires of the vehicle's widest axle) must be 35.0 cm or less. Other parts of the vehicle (eg., axles) may exceed this 35.0 cm width.

So you can have you axles as long as you want, but keep in mind that the ramp + the car in the launch position has to fit in a 100cm h x 75cm l x 75cm w box, which makes your maximum axle length is 75 cm. (That's a long axle!)

[questionguy]

Any ideas so far on a good release mechanism?

[engineeringmaniac]

Any ideas so far on a good release mechanism?

What I was thinking of was to have a small eyelet, such as in a basic hook and eye latch that can be bought at any hardware store, attached to the back of the vehicle. A piece of string would be attached to the top of the ramp and have a loop at the other end. The two loops (string and eyelet) would the overlaid, and a small pin put in-between them to hold the car in place. A different sting could be attached to the bottom of a pin that would then go down through a hole on the ramp surface to the bottom of a ramp where it would attach to a lever (class 3 probably). Simply push the lever with the pencil eraser and pull the pin out.

This is what I'm most likely going to do, although I'm currently building and testing ramps so I haven't tries it yet. It seems simple to build and fairly consistent, well in concept anyways. The string length could also be adjusted on the 2nd run to adjust for time.

[fishman100]

I was thinking of something like a "claw" that's attached to the top of the ramp with a set of hinges. There would be a small piece of wood/metal directly above the ramp that's also connected to the hinges. The claw would latch onto the rear axles and would release the car once you pushed small wooden/metal piece backwards (thus lifting the claw from the axle). Lik engineeringmaniac I have not experimented with this idea yet.

[illusionist]

I was thinking of something like a "claw" that's attached to the top of the ramp with a set of hinges. There would be a small piece of wood/metal directly above the ramp that's also connected to the hinges. The claw would latch onto the rear axles and would release the car once you pushed small wooden/metal piece backwards (thus lifting the claw from the axle). Lik engineeringmaniac I have not experimented with this idea yet.

That is similar to what I was designing. A lever that simply holds onto the vehicle at one end, and pivots (fulcrum) at the very top of the ramp.

[questionguy]

I was thinking of something like a "claw" that's attached to the top of the ramp with a set of hinges. There would be a small piece of wood/metal directly above the ramp that's also connected to the hinges. The claw would latch onto the rear axles and would release the car once you pushed small wooden/metal piece backwards (thus lifting the claw from the axle). Lik engineeringmaniac I have not experimented with this idea yet.

That is similar to what I was designing. A lever that simply holds onto the vehicle at one end, and pivots (fulcrum) at the very top of the ramp.

So is that similar to a toll booth, that's what I was thinking would be one of the ways for a release mechanism, but it would have to be strong to hold the vehicle back.