Rule and letting weight move

[Jewel]

Just reading over the standard rules, and this may be the dumbest question ever, but can the driving weight of the car be allowed to move a bit? Could it jiggle around or move in a slot?

Thanks!?!

[Stan Pope]

Just reading over the standard rules, and this may be the dumbest question ever, but can the driving weight of the car be allowed to move a bit? Could it jiggle around or move in a slot?

Thanks!?!

Depends on local rules! The "Rules in the Box", IIRC, don't restrict moveable solids inside the car. Many local rules do prohibit them.

[Jewel]

Let's say the angle of the starting ramp is about 30 degrees. Has anyone every made a cylindrical driving weight that would rest on an internal ramp that is part of the car body that would slope in the opposite direction of the starting ramp and with an angle of less than 30 degrees?

What I am saying is that with a mobile weight can you get more potential energy created? During the transition point the driving weight could be made to fall a further distance and some of the potential energy could be converted into more kinetic energy. Anybody ever try this trick?

[Stan Pope]

There are multiple ways to apply moveable weights to advantage. All that I have seen need to be "cocked" by the person staging the car, presumedly the owner.

So, you need these two conditions before even thinking about using:
1. Rules allow (most do not.)
2. Owner stages car (many do not)

Include in your energy analysis, the ratational inertia of the cylinder as it rolls down the ramp. It must be of significant mass to have any meaningful effect on the car. It's rotational inertia will put that of those heavy BSA wheels to shame! So, you should expect this car to be "slow off the line."

There does not seem to be any way to recapture the energy expended in rolling the cylinder. Weighted BSA wheels at least give back the energy stored in them.

The advantage remains that the car's CM is moved back after the car leaves the start line without a major loss of potential energy. This is good because the track is "shortened" by the CM's movement.

[Go Bubba Go]

Let's say the angle of the starting ramp is about 30 degrees. Has anyone every made a cylindrical driving weight that would rest on an internal ramp that is part of the car body that would slope in the opposite direction of the starting ramp and with an angle of less than 30 degrees?

What I am saying is that with a mobile weight can you get more potential energy created? During the transition point the driving weight could be made to fall a further distance and some of the potential energy could be converted into more kinetic energy. Anybody ever try this trick?

We haven't actually played with it as it is against our local rules to have any moving parts such as this, but once in a while I do consider the concept.

Two downsides (first glance, not sure) to your suggested configuration:

1) Given that there is an overall weight limit, the COG with your mobile weight in the forward/up position would be further forward than it will be in it's final position. COG rearward in the final position is limited by stability issues, so in the forward/up position you would likely have your COG further forward of your typical "ideal" location. Any gain you have from moving the weight upward and then letting it fall might be offset (or a net loss) from the loss you have in moving the weight forward before it returns to the rear.

2) The weight sliding toward the back of the car might actually end up providing a "push" rearward as it descends the ramp and bumps against whatever stops it from rolling off the back. Not sure about this, again since we can't do it I haven't thought it through much.

However, if a weight moving down an onboard ramp were to provide an added "push" in the direction of the downslope of the onboard ramp, I could see setting up an onboard ramp in the forward direction, with the mobile weight being held back by a trigger pin that dropped out when the car went through the transition. If this could be accomplished, you could build a car that when flat actually had a COG directly above or even slightly behind the rear axle with the weight in the upper position. When placed on an angle on the ramp (depending how far behind the axle you went with your COG), you could have a COG in front of the rear axle (i.e. stable) on the ramp. As long as the weight dropped fast enough during the transition to keep the effective COG ahead of the rear axle, you could gain something from your ability to start with a COG further back on the ramp. If the weight does not move forward fast enough and the effective COG moves behind the rear axle, you pop a wheelie.

Or perhaps use a couple large ball bearings and a "double ramp". The upper ramp would be as you described, but quite short (long enough only to hold the ball bearings in the upward position). The lower ramp would deliver the balls forward from the rear all the way to the front after they dropped from their initial position during the transition. This design would have a bit more risk in the "wheelie" department, I think.

Only some thoughts, haven't really pondered it that long. But now you've got me thinking about where I could get some really heavy ball bearings for next year's Open Class.

[PWD]

With our pack rules which are pretty typical you can not have any moving parts. So I have always interpreted this to mean no moving weights

[SlartyBartFast]

There does not seem to be any way to recapture the energy expended in rolling the cylinder.

Best to go with a supported weight. At least, if the weight is moving on a ramp, the weight should be non-rotational. If necessary, small wheels or bearing on the inside ramp to help the motion.

Perhaps the weight could be on a four arm linkage type support that would swing the weight down and forward.

In any case, does the motion have to occur at the transition for best effect?

If the movement was triggered by the drop of the gate (a mechanism in the nose perhaps), the gain in speed would be instant and benefit the car the length of the track. The energy transfered from PE to KE should be the same. But as it occurs earlier, the difference at the finish line would be inches more...

[Doug-in-the-woods]

As far as movable weight, I have seen a very fast, well performing car that used a tube burried inside the car and the tube had mercury in it.
The weight moved very freely making the car very fast.

[PWD]

I always thought the mercury thing was folklore.

I do know a few years ago a dad used mercury in his son PWD car which then spilt and they had to evacuate the school. The story actually made national news.