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Old 02-12-2015, 08:48 AM   #5461
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Originally Posted by Worst87 View Post
Excellently described wingracer! Maybe this is a bit over the top, but:
Would you agree with me that a modern TC setup with a spool up front tends to have better steady state and transition performance when it has a bit more rear than front statical weight?
Reason i think that: While steady state the spool creates a yaw decreasing torque and let the car understeer. With a rear-heavier car and same tyres you need to increase front roll stiffness to get the same handling. So the wheel load alteration on the front is higher which in turn will have the spool to create less of the unwanted understeer because the inner front wheel will have just less vertical load!

And to bring the argumentation to an end: I think, that when using the FMC, and therefore more statical weight at the front, you should start thinking about a gear diff up front. Because the negative side effects with the spool will become more apparent while ALSO the advantage in traction, so longitudinal performance, of the spool diminishes!

Would you agree?
To be honest, I rarely race TC and when I do it is usually with a front diff so I can't comment on the specifics but you seem to be on the right track. It's nice to see someone talk about yaw moments. That's a staggeringly un-understood aspect of handling yet is one of the primary reasons for some of the weird counter-intuitive things that go on in race cars like front toe effects. It's particularly critical with a locked 4wd system.
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Old 02-12-2015, 02:07 PM   #5462
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Something I wrote a few years ago:


1. Static weight distribution.

The effects of changing a car's fore/aft weight distribution is probably the most commonly misunderstood adjustment in all of motorsports. It sounds simple enough, want more steering, move weight forward right?

Nope. It's the exact opposite of what you think. Let me see if I can explain it. There are two reasons for the effect.

When you add vertical load to a tire, it gains traction. But if you put them both on a graph, you will see that the traction goes up less than the load is going up. For example, take a tire with a 1 pound vertical load on it, let's say it can also take 1 pound of lateral load before it slides. Now double the vertical load to 2 pounds. Does it now take 2 pounds of lateral load to make it slide? No, it will slide at a lesser lateral load, let's say 1.8 pounds.

Secondly, if you move static weight forward in the car, you are putting more vertical load on the front tires but you are also moving the center of gravity forward. Obviously I am talking about the fore/aft position of the cg, not the height. The cg is the point on the car where centrifugal force pushes on it to try and push the car towards the outside of the corner. Let's see an example of how this might affect things.

Imagine a 1 pound car. It has the exact same tires all the way around and its weight distribution is exactly even, 1/4 pound of weight on each tire. Its fore/aft cg position will be right in the middle of the car between the tires. Now let's say skid pad tests show this car can take a 1 pound lateral load before skidding, meaning it can corner at 1g and it's perfectly balanced handling wise so when it skids, it's a four wheel drift out of the circle, not a spin out or an understeer out of the circle. If you doubled the car's weight to 2 pounds, the tires will gain more traction but not as much as the weight will increase the lateral load so the car will now skid with a 1.8 pound lateral load which is LESS than 1g with a two pound car.

Now let's go back to the one pound car but let's move some component forward so that the front tires now have more weight on them. This would initially seem to increase front traction so now this car will spin out when it skids instead of a nice, balanced, 4 wheel drift right? No, that's wrong. Remember, traction goes up more slowly than the vertical load does. So what happens is that the now more lightly loaded rear tires have lost less traction than the fronts have gained. But this alone is only part of the story since we are still seeing a loss of rear traction and a gain in front, even if it isn't an even trade.

That's where fore/aft cg location comes in. Imagine the original, balanced car is stationary on the skid pad and you are in the middle of the skid pad with a pool cue to use to try and push the car from the side out of the circle. The end of the pool cue is placed right on the cg (middle of the car) and the tires and load are the same so when you push on the cue, the car just slides all four tires. Now move the weight forward. The cg moves forward so you have to move the spot on the car that you push with the cue forward. This means you are now pushing harder on the front tires than on the rear. This would be balanced out by the increase in front traction and the decrease in rear traction resulting in another perfect, four wheel slide except that as I said before, the rears have lost less traction than the fronts gained. So the front tires are going to slide first. The car will now understeer.

I hope that makes sense. I am not the best at clearly explaining complex concepts of vehicle dynamics but I have studied it extensively and this is the basic consensus of ALL well informed engineers on the subject. This is why nose heavy front engined cars fight understeer issues while tail heavy rear engined cars like 911s fight with oversteer.

Also, this subject can get even more confusing due to another effect. As I described above, moving the weight to the rear should make the car oversteer but there is a situation where this could be backward. Moving the weight back will make the car looser in a steady state corner but with a rear wheel drive car, the increase in rear weight could reduce wheel spin under power, improving rear traction. This is why offroad dirt cars have such a high rear weight distribution. So in this situation, moving the weight to the rear could result in more steering off power but less on power. Especially when powering off of a slow corner, but might have even MORE on power steering exiting a fast corner. And if that wasn't confusing enough, having that motor slung out in back also gives the car a high polar moment of inertia, making it less responsive. Moment of inertia is a whole different subject to be addressed later.
After reading this just ordered my new car with the conversion kit too, hope to have that up and running in the next few weeks
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Old 02-13-2015, 02:52 PM   #5463
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guys, what is it about the blue vs black bladders and the single vs double o-rings? What did you feel? i felt nada...


thanks
Paul
I am not sure about the bladders. I use the black bladders, yes, but because nearly every single setups uses them I honestly never even tried the stock bladders.

The double o-ring is used to help with setting rebound, so I am not sure how much of a change you would expect to feel on the track (very slight.) I think you would just expect the car to be a lot more consistent on all four corners since your rebound can be a lot more precisely matched than with the single o-ring.
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Old 02-14-2015, 02:57 AM   #5464
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For a while now I have been looking at getting a new car and weighing up options on what to buy. I have been racing a TOP Photon EX for the past 2 years but I've been noticing the car is starting to get harder to stay up the pointy end of the field. Being in Sydney, Australia we mostly have to order parts from overseas but some cars are available locally and I wanted to make sure that if I needed spares I can head up to the hobby store and pick up the part I needed rather than pay for shipping on what could be a $5 steering knuckle.

So about 2 weeks ago a friend of mine loaned me her car, a 2014 BD-7, and all I did was place my receiver in the car, trim the steering, and finished 3rd out of about 25 racers with very little effort. Let's just say that the choice was made and earlier this week I went and picked up a Chassis from Hoot RC and started building it yesterday.

At the moment I've completed the build (Still need to put oil in the diff and shocks, as well as put in the electronics that are on order) and I can honestly say that this simply was a beautiful car to build. Only thing I had to modify was the centre pulley as I fitted a Kawada Spur that's a little thicker than the stock one, but that was all sorted by changing the screws from button heads to countersunk, thus allowing the pulley to sit a fraction closer to the spur and prevent the bearings from binding up.

All in all, I'm one happy racer and I'm looking forward to racing the new car when I complete the full build.
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Old 02-14-2015, 08:32 AM   #5465
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Originally Posted by NuttsnBolts View Post
For a while now I have been looking at getting a new car and weighing up options on what to buy. I have been racing a TOP Photon EX for the past 2 years but I've been noticing the car is starting to get harder to stay up the pointy end of the field. Being in Sydney, Australia we mostly have to order parts from overseas but some cars are available locally and I wanted to make sure that if I needed spares I can head up to the hobby store and pick up the part I needed rather than pay for shipping on what could be a $5 steering knuckle.

So about 2 weeks ago a friend of mine loaned me her car, a 2014 BD-7, and all I did was place my receiver in the car, trim the steering, and finished 3rd out of about 25 racers with very little effort. Let's just say that the choice was made and earlier this week I went and picked up a Chassis from Hoot RC and started building it yesterday.

At the moment I've completed the build (Still need to put oil in the diff and shocks, as well as put in the electronics that are on order) and I can honestly say that this simply was a beautiful car to build. Only thing I had to modify was the centre pulley as I fitted a Kawada Spur that's a little thicker than the stock one, but that was all sorted by changing the screws from button heads to countersunk, thus allowing the pulley to sit a fraction closer to the spur and prevent the bearings from binding up.

All in all, I'm one happy racer and I'm looking forward to racing the new car when I complete the full build.
Good choice in getting a Yokomo
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Old 02-14-2015, 10:25 PM   #5466
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Hi, I recently just built a new BD-7 which i purchased from Amain Hobbies. I built it with the forward motor conversion. After building it i realized that as you look down at the car(front facing away from you) the right side of the spur gear is rubbing on the top deck. It looks to me as if the holes were not drilled properly. Has anyone else ran into this issue?
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Old 02-15-2015, 02:11 AM   #5467
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Hi, I recently just built a new BD-7 which i purchased from Amain Hobbies. I built it with the forward motor conversion. After building it i realized that as you look down at the car(front facing away from you) the right side of the spur gear is rubbing on the top deck. It looks to me as if the holes were not drilled properly. Has anyone else ran into this issue?
Hey Kobiwan,

If you have a look at my post above I made mention to an issue with the Center Gear Assembly where I had a similar issue and it was mentioned how a few things will cause that issue as well as other similar problems, but most can hopefully be easily fixed.

The Spurs that are designed for the car are Panaracer spur gears which are a thinner gear than what I used when I put my car together. I used a Kawada spur and I had the problem where the Center assembly was binding up. I resolved that issue by swapping the 4x 5mm button head screws for 4x 6mm flat head screws. Because of where the screws are measured (button heads being from below the cap, flat heads being above the cap) it allowed the two drive pulleys to sit closer together and thus they didn't bind up.

After sorting that out I still had a problem where both the spur was narrowly touching the top deck in the very corner and the side of the pulley was binding against the same side of the deck. It was then that Beth mentioned that my pulley was actually on backwards and it in turn moved the whole mechanism sideways.

The only other options I can think of is swapping the spur for a thinner one that will narrow the pulley even more, or a possible thinner bearing on the motor mount end with some shims on the other to help center up the pulley.

Hope that helps.
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Old 02-15-2015, 07:16 AM   #5468
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Originally Posted by NuttsnBolts View Post
Hey Kobiwan,

If you have a look at my post above I made mention to an issue with the Center Gear Assembly where I had a similar issue and it was mentioned how a few things will cause that issue as well as other similar problems, but most can hopefully be easily fixed.

The Spurs that are designed for the car are Panaracer spur gears which are a thinner gear than what I used when I put my car together. I used a Kawada spur and I had the problem where the Center assembly was binding up. I resolved that issue by swapping the 4x 5mm button head screws for 4x 6mm flat head screws. Because of where the screws are measured (button heads being from below the cap, flat heads being above the cap) it allowed the two drive pulleys to sit closer together and thus they didn't bind up.

After sorting that out I still had a problem where both the spur was narrowly touching the top deck in the very corner and the side of the pulley was binding against the same side of the deck. It was then that Beth mentioned that my pulley was actually on backwards and it in turn moved the whole mechanism sideways.

The only other options I can think of is swapping the spur for a thinner one that will narrow the pulley even more, or a possible thinner bearing on the motor mount end with some shims on the other to help center up the pulley.

Hope that helps.

Thank you the help. I currently use the Panaracer spurs. I tried the flat head screws and it didn't make a difference. I was just left with a gap between the pully and the head of the screws. So I ended up just turning the top deck over and it is now centered. Technically that's not the way it is suppose to go due to the countersunk hole for the belt guide. But i don't use the guide anyway.
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Old 02-15-2015, 09:02 AM   #5469
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Originally Posted by kobiwan View Post
Thank you the help. I currently use the Panaracer spurs. I tried the flat head screws and it didn't make a difference. I was just left with a gap between the pully and the head of the screws. So I ended up just turning the top deck over and it is now centered. Technically that's not the way it is suppose to go due to the countersunk hole for the belt guide. But i don't use the guide anyway.
Are you certain you have installed everything correctly ?
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Old 02-15-2015, 09:31 AM   #5470
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Are you certain you have installed everything correctly ?
Yeah, I made sure I double checked the manual. I have been known to put stuff together wrong LOL. I talked to a race buddy and he said his top deck is upside down as well. I think it might be a manufacturing flaw in the top deck that comes with the foward motor conversion.
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Old 02-16-2015, 07:26 PM   #5471
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I had to grind the top deck to clear a motor, besides that everything went on fine. Reading the posts in checked the FMCs that I have and they're all the same. Should clear spur perfectly fine.
On another note DHL dropped this off today, many thanks to Denis Z at EX lab.
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Old 02-17-2015, 12:08 AM   #5472
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Originally Posted by NuttsnBolts View Post
For a while now I have been looking at getting a new car and weighing up options on what to buy. I have been racing a TOP Photon EX for the past 2 years but I've been noticing the car is starting to get harder to stay up the pointy end of the field. Being in Sydney, Australia we mostly have to order parts from overseas but some cars are available locally and I wanted to make sure that if I needed spares I can head up to the hobby store and pick up the part I needed rather than pay for shipping on what could be a $5 steering knuckle.

So about 2 weeks ago a friend of mine loaned me her car, a 2014 BD-7, and all I did was place my receiver in the car, trim the steering, and finished 3rd out of about 25 racers with very little effort. Let's just say that the choice was made and earlier this week I went and picked up a Chassis from Hoot RC and started building it yesterday.

At the moment I've completed the build (Still need to put oil in the diff and shocks, as well as put in the electronics that are on order) and I can honestly say that this simply was a beautiful car to build. Only thing I had to modify was the centre pulley as I fitted a Kawada Spur that's a little thicker than the stock one, but that was all sorted by changing the screws from button heads to countersunk, thus allowing the pulley to sit a fraction closer to the spur and prevent the bearings from binding up.

All in all, I'm one happy racer and I'm looking forward to racing the new car when I complete the full build.
Cannot disagree. I am running my third one, only changing to the newer versions so as to be able to follow top guys with their setups.
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Old 02-17-2015, 12:13 AM   #5473
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Originally Posted by kobiwan View Post
Thank you the help. I currently use the Panaracer spurs. I tried the flat head screws and it didn't make a difference. I was just left with a gap between the pully and the head of the screws. So I ended up just turning the top deck over and it is now centered. Technically that's not the way it is suppose to go due to the countersunk hole for the belt guide. But i don't use the guide anyway.
Panaracer are the brand Yokomo use as stock so they should fit in perfectly. Are you using stock buttonhead screws cause the head thickness varies with the different brands. Anyway, does the gap make any difference in the final alaignment of the spur and side pulleys or does it make it loose or bind? If not i would not bother.
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Old 02-17-2015, 06:52 PM   #5474
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Chassis Corner Balance Using Digital Scales

https://www.youtube.com/watch?v=WEj7tZyR56Y


Checking and Setting your Anti-Roll Bar

https://www.youtube.com/watch?v=bA-3qY7bIwg


I hope these videos will help you out with setting up your car
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Old 02-18-2015, 05:04 AM   #5475
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Hello guys. Just picked up and built a BD7 '15. First shake-down day last Sunday and I'm having an issue with the steering linkage. Both of the retaining screws on the center link are working loose from the bell cranks during normal steering. I haven't found any unusual binding, I can visually see the screws working loose as I manually move the linkage. I figured I can always loctite the lower points, or use longer screws and put locknuts on, but it seems like those are a bandaid fix and there is something else going wrong. Thoughts?
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