weight vs. psuedo-weight

[burad]

I have a technical question on achieving weight with lead vs. achieving a pseudo-weight ('downforce') with magnet(s).
If I have a magnet car that has a pseudo-weight of 275 grams when it's on the magnet marshal, it seems to me there's a difference in the physics of cornering compared to having it weigh 275 grams due to lead and no magnet. Even if the weight is in the place the magnet goes.
A car with 275 grams total downforce will suddenly weigh significantly less the instant the magnet(s) get a certain distance away from the rails. Whereas as car that is weighted to 275 grams will always weigh 275 grams, which seems like it would make the car remain relatively 'grippier' once it's not in an optimum position over the rails, as long as it's still in the slot. Is this true?

bradg

[Ember]

No doubt Doc Fabio can explain it all properly.

The magnetic attraction is extra to the cars weight. Isn't magnetic force a strong force where gravity is only a weak one? Crumbs my physics classes were too long ago.

[Ember]

Thanks Johnny. That's kind of where I was trying to go, but the thoughts fizzled out in the heat.

[2FER SLOTS]

No momentum in attraction.....might even be a momentum dampner :sci-fi-marvinmartian:

[RichD]

It is not likely that anyone would want to build a 1/32nd car that weighed 275 grams! Cars with magnets effectivly have a much lower center of gravity than cars that use weights, even if you put the added weight on the bottom of the car. With magnets you can have the grip without needing all that extra mass, however you still get the drag that a car with the same amount of weight would have so the motor has to work as hard. The problem that I have with cars that use magnets is the all-or-nothing nature of the added grip. Before we stopped using magnets alltogether we moved the magnets forward so the cars would slide a little before they left the slot. Most people that run without magnets reduce the track voltage. We have found that the cars's top speed and acceleration are about the same because of the reduced drag.

[chappyman66]

If it's green it's biology; if it smells it's chemistry; if it doesn't make sense it's physics....:lol:

No, cornering with a 275g car will not be the same as cornering with a car that has a magnet of 275g downforce. As already pointed out, the location of the magnet affects downforce due to the lateral acceleration (the force of the rear of the car swinging out in the corner). The early Nincos and many Carrera Evo 1/32 cars had "weak" magnets behind the front axle that didn't affect the handling nearly as much as the rear mounted neo magnets in the Fly cars. Because the front axle location creates a longer moment of rotation (probably not the right term, someone will correct me) the car can slide a bit because the front end doesn't move as much as the rear does and therefore you still have some magnetic downforce because the front end is still partly over the rails when the rear end is hung out in the corner. This is not the case with the rear magnet because once you apply more force than the magnet applies you break the attraction and all of that downforce is immediately lost causing the massive crashes.

Also note that magnets follow the inverse square law, meaning that doubling the distance from the rails causes a 4X reduction in the amount of downforce (halving the distance is a 4X increase) so ride height and tire diameter matters a great deal.

Note that with lead/brass you can't precisely locate the cg the way that a magnet does. Johnny got it right with chassis stiffness/flexibility which is why you see "flopper" pan chassis instead of straight "jail door" designs since the hinges allow the weight to "move" which creates better handling. Which is of course why you have pod chassis and you loosen body screws to let the bodies "float" ;)