Weight placement question

[Thinkin'Bout Racin]

I am not sure that what you are saying is making sense. How are you measuring your COG?

Also remember that when you move weight, that the amount of weight is important, but also very important is how FAR you move that weight. Think of a teetter-totter ...when the big weight is closer to the fulcrum, the less leverage it has.

So how far you move the weight from the COG has a big effect on how much it changes the COG. Clear as mud. Remember that you are not moving the entire 2.5 oz canopy behind the COG and even if it is, some of it is just barley behind the COG.

If you can weigh your f FDW (front dominate wheel) it will answer a lot of questions! Since you have a scale, you can weigh it by finding some books, wood or something that you can place under the rear wheels to make the car sit level with only your FDW on the scale. This won't be exact, but it will tell us a lot.

While you have this set up, try moving your weight around. I will be very surprised if you can get the weight of your DFW under 18-19 grams. If so, DON'T worry about COG. You will have PLENTY of weight on the front!

 

[John-newbie11]

I am not sure that what you are saying is making sense. How are you measuring your COG?

Also remember that when you move weight, that the amount of weight is important, but also very important is how FAR you move that weight. Think of a teetter-totter ...when the big weight is closer to the fulcrum, the less leverage it has.

So how far you move the weight from the COG has a big effect on how much it changes the COG. Clear as mud. Remember that you are not moving the entire 2.5 oz canopy behind the COG and even if it is, some of it is just barley behind the COG.

If you can weigh your f FDW (front dominate wheel) it will answer a lot of questions! Since you have a scale, you can weigh it by finding some books, wood or something that you can place under the rear wheels to make the car sit level with only your FDW on the scale. This won't be exact, but it will tell us a lot.

While you have this set up, try moving your weight around. I will be very surprised if you can get the weight of your DFW under 18-19 grams. If so, DON'T worry about COG. You will have PLENTY of weight on the front!

I'm measuring cog by placing car on a sideways ruler to the point where it balances. That's about 3/4" in front of rear axle.

Right now, the center of the dome is between the cog and the rear axle, slightly closer to the cog. If I move the dome back a little more, closer to the axle, it makes the cog smaller (and I don't believe I want it much smaller than 3/4, but I could be wrong).

As for measuring the DFW, I'm not sure I'm following. I understand what you're saying about getting the car level with the scale, and only placing the fdw on the scale, and you said it won't be exact, but will it really be accurate at all? Even if I think the books are level, It won't be exact.

In any case, I'll give it a try and see what happens.

 

[John-newbie11]

Just another example, if I were to move the dome directly over the rear axle, and keep the 1 ounce in the very rear, cog would be at 1/2" or less. too small I assume? if the dome is between where it is now and rear axle, cog is then between 1/2 and 3/4. So there's definitely some play as I move the dome back a bit, but again, i'm not sure if i'm then putting to much on/behind the axle.

 

[DuckOfAllTrades]

This thread makes my head hurt!

 

[B_Regal Racing]

Without reading 70-ish posts, I'm going to assume that this car is a 3 wheeled rail rider. If so, you only have one front wheel that touches the track and steers the car into the rail. This is the Front Dominant Wheel, or FDW. Instead of concentrating on the COG, focus on the weight on the FDW. Measure the weight that the FDW carries. With the car fully assembled, place the FDW on the scale. Raise the back wheels so they are level with the FDW (use a book or something). If the weight on the FDW is 16 to 18 grams, you'll have no problem. The weight each wheel is carrying is far better indication how a car will perform than is trying to balance it on a ruler (and its more precise). I do not know of a pro who measures COG, but I can assure you that the top racers know exactly how much weight is on each wheel, especially the FDW.

 

[John-newbie11]

Thanks so much. I'll definitely try to weight the FDW.

I do apologize for all the back and forth and various iterations of the same question...

 

[John-newbie11]

Without reading 70-ish posts, I'm going to assume that this car is a 3 wheeled rail rider. If so, you only have one front wheel that touches the track and steers the car into the rail. This is the Front Dominant Wheel, or FDW. Instead of concentrating on the COG, focus on the weight on the FDW. Measure the weight that the FDW carries. With the car fully assembled, place the FDW on the scale. Raise the back wheels so they are level with the FDW (use a book or something). If the weight on the FDW is 16 to 18 grams, you'll have no problem. The weight each wheel is carrying is far better indication how a car will perform than is trying to balance it on a ruler (and its more precise). I do not know of a pro who measures COG, but I can assure you that the top racers know exactly how much weight is on each wheel, especially the FDW.

Not sure I did it right, but I got .9 ounces, or 25.5 grams. The entire car (with nothing at all attached) is 1 ounce when placed on the scale.

 

[Thinkin'Bout Racin]

With the car assembled and the weight where you think you want it, like I said you probably would have 20-22 grams on the FDW. It appears that you have 25+ grams on the FDW. If so, it would not be possible to move too much weight to the back with the weight options you have considered.

Try moving as much weight rearward as you can while you have the FDW on the scale I would be shocked if you can get it down to 19 grams. Having said that if you could get it down to 16-18 grams that would be considered decent for a Scout car. Really fast Scout cars have a FDW weight of around 14 grams + or -.

In my humble opinion, you will not have a COG that is too aggressive on this car. If the car is unstable and wiggles it will NOT be because of your COG. It will be one of the other things I mentioned before.

Thanks to B Regal for trying to help out! He is a great source of information for newer people!

Just so you know, I checked quick and calculated your COG based on a 25 gram FDW weight. The actual number depends on what your wheel base is, but your true COG is around .870" + or -. It is not currently at .750", maybe that will give you some comfort about where to place the weight.