COM, Wheel base, Steer- How I see it

[Quicktimederby]

So how I see it is everything effects everything. I have also learned that there is not a one set COM, WB, or amount of steer that works best. Now with that being said I do believe that there is a perfect amount of force that needs to be applied to the rail to make the smoothest and fastest run. I believe that the perfect amount of force is the same no matter COM, or WB. The way that the force is adjusted is by the steer. I gotta get back to work more to come. Start thinking about the center of COM and the way the WB adjust the amount of leverage. See what you come up with. Hopefully this makes some sense.

 

[derby freak]

I have to say qt and I beleive that the com and wb effect the stability of car therefore reducing the amout of force needed against the rail to have a smooth run. Less force = less friction = faster car. Friction is the key here IMO, the more friction you can reduce the faster your car will run down the track and there is many areas for friction between the track and the car. EXAMPLES: axle to wheel bore, DFW to center rail, rear wheel toe in or out, DFW inner hub to car body and rear wheel outer hub to axle head. basically what I'm saying is, there are many areas where you can reduce friction and the more you reduce, well the faster the car.

 

[GravityX]

I'll chime in with my 2¢ worth. First of all, I have to agree with the statement regarding everything effects how the car runs down the track, WB, COM and steer. As with anything there is a point of near perfect operation and in this case it's a combination of the 3 attributes noted. I also agree with what DF said here "the COM and WB effect stability". I believe the more aggressive the COM the more steer may be needed to stabilize the car and at the same time a longer WB will help stabilize allowing for less steer. Ultimately we are looking for the least amount of friction as the car heads down the track for the fastest times without sacrificing stability. It's a fine line.

When we measure COM, typically we measure one plane only, and this is the balance point just forward of the rear wheels (call this fCOM). There is also the COM of left to right, in other words, it is the point at which the car will balance side to side (call it sCOM). You'll likely find that sCOM will lie on the fCOM plane and is typically not equidistant from the either side of the body. Then there is, what I'm going to call total COM (tCOM) and this is the point at which fCOM and sCOM intersect. In other words, this is the point at which your car will balance on the point of a pencil. This is because of weight placement and typically the DFW side of the car is heavier than the non DFW side. There is a thread that talks about this and states that tCOM should lie within a triangulated area. I think there are some racers here that use three scales to measure weight on each wheel. I personally haven't used this method, but I will place more weight on the DFW side of the car when weighting to keep tCOM within the this triangulated area.

Now regarding how WB and COM effect steer. The body without wheels has a fixed COM, add wheels and you move the COM around. This is how I see it, a longer WB will move COM forward and shorter WB moves COM rearward (but not rearward of original COM, but only in comparison to Longer WB COM) and with an SP build COM is moved sideways also, when wheels are added to the body. Now, I think a longer WB car requires less steer and a shorter WB needs more steer because of what I'm going to refer to as leverage from the WB.

Now, I'm not sure if this is what was being sought, but it was what was on my mind after reading the post. Now, do I put this much thinking into each build, NO! I wouldn't have one car built if this were the case. I believe it is just some of the theory behind what we are trying to achieve here. Oops, I said more than my 2¢ worth.

So how I see it is everything effects everything. I have also learned that there is not a one set COM, WB, or amount of steer that works best. Now with that being said I do believe that there is a perfect amount of force that needs to be applied to the rail to make the smoothest and fastest run. I believe that the perfect amount of force is the same no matter COM, or WB. The way that the force is adjusted is by the steer. I gotta get back to work more to come. Start thinking about the center of COM and the way the WB adjust the amount of leverage. See what you come up with. Hopefully this makes some sense.

 

[g.o.racing]

Well G.X.
That's alot of info for 2 cents how much can I get for a dime?
I'm not at that level yet but I do think that all that stuff will be important to get the last few thousands we will need to keep up with the big dogs!!!!

 

[bracketracer]

It's funny that some builders say "Don't worry about the COM, just cluster the weight around the rear axle and it'll be fine." Then there's other builders that analyze it down to a single point in space. And both camps can build fast cars!

I don't have much experience building since I'm new, but I really thought there is one ideal setup that will be the optimum. I would be glad to hear that's not the case, because that would mean there are many more correct solutions that I might accidentally stumble across one!

 

[Chief]

That's funny G.O. I was thinking the Xact same thing haha...Be careful what you ask for though haha.
I can totally relate to Bracketracer too, I have talked with lots of guys and it is as you say from one end of the spectrum to the other, some builders Analyze and re-analyze over and over and seem to have a pretty fast car and then there are the guys that just slap some stuff together and send it down the track with great results. That is what makes this racing so much fun...there are a million ways of doing the same thing and the results are with in milliseconds quite amazing actually, but one of the most important things that I have learned is that EVERY car is different even if you build them the Xact same way at the Xact same time???

Well G.X.
That's alot of info for 2 cents how much can I get for a dime?
I'm not at that level yet but I do think that all that stuff will be important to get the last few thousands we will need to keep up with the big dogs!!!!

 

[Quicktimederby]

Alright let's see if I can finish my thoughts. First off I do very much agree that the less friction the faster, and I very much like GX's views and I'm going to build on them. Lets look at what he calls tCOM the tCOM is the pivot point on the car, or the center location of the weight. So if my thinking that there is a set force for that perfect set up, the longer the WB the greater amount of leverage and there for less steer is needed to achieve the perfect force. This does not mean it will be faster or produce less friction at the perfect force, it should be the exactly the same as a smaller WB car with the perfect force. Now if you do not hit that perfect force than the WB, COM, and steer can drastically effect the performance

 

[GravityX]

Weekend rates.

Well G.X.
That's alot of info for 2 cents how much can I get for a dime?
I'm not at that level yet but I do think that all that stuff will be important to get the last few thousands we will need to keep up with the big dogs!!!!

 

[Guest]

MERKIN THE WORLD!!!!

 

[Skidogg Racing]

 

[Skidogg Racing]

GX lol

 

[GravityX]

Let's add one more thing to the mix QT that no one else has mastered as well as one and call it side force. This obviously plays a factor if harnessed correctly, done incorrectly and it's just a copycat design that doesn't work like an original. There is more to it than just what it appears to be. This design takes advantage of all the elements and does it well. Now, does this design allow for less steer because of it, I think so, but only countless hours of testing and trials can prove it and has been proven by one. Will the code be cracked by others, someday I'm sure. Until then, keep testing and try again.

 

[Skippy Kicky]

I'm enjoying this post. Thanks all for sharing and inspiring me to do some testing. I made some changes on my SS and had to give it a lot more steer. I am thinking I will try moving the COG forward attempting to lessen my "side force".
Thanks guys!

 

[W&K Creations]

One of my SS cars at the Nationals had its COM at 3/4" in front of the rear axel with as much weight moved toward the back as possible otherwise but due to my own error, only had 2" of steer over 4 feet on my makeshift tuning table (I wont go into why I couldnt tune it to steer more LOL...)

I had it marked to be staged so the FDW was on the rail to start rather than just off the rail (standard if no instructions as per 5 kids post of staging)....and despite the relatively small steer, the recently posted videos show no evidence of wiggling or instability as far as the runs down the track...

and yet, despite the same prep, weight, set up etc with one of the other cars at nationals, it ran .02 seconds slower than the one with more steer (4" over 4 feet)....was that due to earlier rubbing on the rail to start? The other car steered more so you could say the car with more steer may have had less total time (small amount really right) on the rail due to the staging but the majority of the time on the track it was steered harder into the rail...but yet was faster in the end....

I agree with everything said thus far and this is a fun discussion to read and think about, and as stated by Chief in this post and certainly otherse in other posts, there is a lot of individual, car specific, variation that can occur due to all the variables that go into making it, thus the importance of paying close attention to that final tuning right before the race in my opinion.

Im sure there is an optimal COM point that takes into account all factors as stated by QT and GX, the trick would be to in making the building process so precise and standardized as to reduce all other possible points of error or deviation, which as we all have experienced, is pretty darn hard to do...well at least for me at this point /images/boards/smilies/smile.gif

W

 

[Quicktimederby]

I guess in my thinking there is a set # of the amount of force that the FDW needs to press on the rail. Some cars do to WB and COM may need 5 inches of steer to achive that perfect # and a different WB, COM car may only 2 inches to archive the same force. I believe there is a set # of force that needs to be applied to the rail. What would be cool is if someone with much more knowledge than me, say like Mario came up with some pressure sensors that could be mounted to a track section that could test the force and see if the fastest possible time for any specific car is the same force as others.

 

[5KidsRacing]

I guess in my thinking there is a set # of the amount of force that the FDW needs to press on the rail. Some cars do to WB and COM may need 5 inches of steer to achive that perfect # and a different WB, COM car may only 2 inches to archive the same force. I believe there is a set # of force that needs to be applied to the rail. What would be cool is if someone with much more knowledge than me, say like Mario came up with some pressure sensors that could be mounted to a track section that could test the force and see if the fastest possible time for any specific car is the same force as others.

I totally agree and I think a poorly set up track screws with this number..... That's what is nice about the NPWDRL track, well set up and you can repeat your numbers. Adding to QT's theory I think this number changes with different types of wheels as well.

 

[GravityX]

QT, that would be an interesting piece of test equipment and would love to see those numbers. Like 5Kids eluded to, there are many variables that will effect this number. I agree with this.

You know, it's topics like this that will keep the wheels turning and interest up for members to try the next "speed secret", you never know who is going to bring the next speed increase to the NPWDRL. As long as there is more speed to be found, I and I'm sure many others, will continue to race the NPWDRL.

Now back to the topic at hand...

 

[W&K Creations]

that would be a nice experiment!

I guess if one had the track and resources and time, you could do your own small trial, take a pretty standard street stock car (as far as WB (5 inches), COM (3/4") and then just tune it to steer more or less at fixed intervals and see the effect on end speed after multiple runs to reduce random error....

once you find the fastest "steer" then for each of the other non-optimal "steer" points (which would be the surrogate for force...I know not perfect at all) see if you can can change one of the other features (move the com by moving weights or changing WB which would much harder as you would have to redrill the axel holes or have multiple holes already predrilled) and reclaim the loss in speed, while still maintaining stability and a nice smooth run.

LOL - of course this would still be racer and car specific and even more so, thats if anyone even has the time to do that.....in between prepping for the actual races themselves....

wait....isnt this just the definition of tuning? LOL damn circular thinking thing...ignore

 

[bracketracer]

I had it marked to be staged so the FDW was on the rail to start rather than just off the rail (standard if no instructions as per 5 kids post of staging)....and despite the relatively small steer, the recently posted videos show no evidence of wiggling or instability as far as the runs down the track...

and yet, despite the same prep, weight, set up etc with one of the other cars at nationals, it ran .02 seconds slower than the one with more steer (4" over 4 feet)....was that due to earlier rubbing on the rail to start? The other car steered more so you could say the car with more steer may have had less total time (small amount really right) on the rail due to the staging but the majority of the time on the track it was steered harder into the rail...but yet was faster in the end....
W

It could just be car to car variation, but I can imagine the wheel rubbing the rail from the start could cause such a time difference. The first, maybe, two feet are the slowest part of the course as the car accelerates down the hill. Anything that restricts the initial acceleration would kill the run. I tried a test where I blew on the back of the car as I pushed the start button and dropped the time by about .020 sec. I couldn't have affected the car for more than a few inches at best. Probably a little more distance than it would roll until it came to the rail if staged with a gap. If there was a way to get a car off the line quicker without a speed penalty later in the run we could see a good reduction in time I would say.

 

[Falcon777]

While there is a lot of emphasis on friction in this discussion, one must remember that to a small degree but important one is aerodynamics and resonance and its effect on stability and speed and of course COM. These are highly technical issues that cannot be measured but could be why similar cars run different times. I still believe the further back the COM is, the more push the cars get down the track and this can overcome a small incremental increase in DFW friction. A shorter wheel base also contributes to a grater push which could also override the very small increase in DFW friction. I think ultimately, like high performance aircraft, you are teetering on the fine line of instability. He who gets the closest without going over that razor thin edge has the fastest car.