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Old 10-21-2014, 07:16 PM   #481
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Hey Martin,

First; I bought your app on the android and have used it a tremendous amount. As soon as I'm done posting this I'm going to grab that subscription to your site as well. Thank you so much for sharing all your information and more importantly your time.

Second; I'm trying to get my head around shock spacing. I made a post about it and got a little insight, but I thought I'd bug you for your thoughts. I'm talking about shimming the shock (both/either top and bottom) away from the shock towers and arms. I understand that some people feel the car is more stable through chicanes and sweepers with the shocks shimmed away from the car. But why does this happen? What's the physics behind it? Also what are the effects of shimming the top or bottom differently versus keeping it straight up and down?

Cheers!!

Luke
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Old 10-21-2014, 08:31 PM   #482
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Martin, I must say the app is very usefull. i use it alot. and i have gotten a couple guys at my track to download it. I find myself using it alot more than I thought i would. Thanks for the great app!
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Old 10-22-2014, 10:54 AM   #483
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Hey Martin,

First; I bought your app on the android and have used it a tremendous amount. As soon as I'm done posting this I'm going to grab that subscription to your site as well. Thank you so much for sharing all your information and more importantly your time.

Second; I'm trying to get my head around shock spacing. I made a post about it and got a little insight, but I thought I'd bug you for your thoughts. I'm talking about shimming the shock (both/either top and bottom) away from the shock towers and arms. I understand that some people feel the car is more stable through chicanes and sweepers with the shocks shimmed away from the car. But why does this happen? What's the physics behind it? Also what are the effects of shimming the top or bottom differently versus keeping it straight up and down?

Cheers!!

Luke
Hey Luke. Yeah, I have seen some drivers do this including Paul Lemieux, but when I tried it, I did not notice any perceptible change. In theory, if the shock is angled more it will provide a softer overall spring rate, but I think the difference is so small that it does not matter so as much.

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Martin, I must say the app is very usefull. i use it alot. and i have gotten a couple guys at my track to download it. I find myself using it alot more than I thought i would. Thanks for the great app!
Thanks for the support guys!!!

It's very rewarding to see people get value out of the learnsetup.com app!

I want to add some functionality to allow people to share their setups to get feedback on what to change to address handling issues. Still trying to figure out the best UI design for this, but will be working on that in my spare time.

Cheers.
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Old 10-22-2014, 02:24 PM   #484
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Hi Martin,
Do you think it's better to have max steering lock to the point you hit track markes due to to much steering and grip,then tune out grip on the front,or just turn down the end point,I ask as I'm struggling to get into the first part of the corners,I was running on high grip and had to turn my steering down to 80%,but I struggled with corned entry and getting out the corner,
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Old 10-22-2014, 11:14 PM   #485
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Hi Martin,
Do you think it's better to have max steering lock to the point you hit track markes due to to much steering and grip,then tune out grip on the front,or just turn down the end point,I ask as I'm struggling to get into the first part of the corners,I was running on high grip and had to turn my steering down to 80%,but I struggled with corned entry and getting out the corner,
My personal view is that it is better to have complete steering throw (lock to lock) and learn how to drive with the additional steering it provides you. If your radio supports this, one thing you can do is add some negative steering exponential into your settings on your radio to make it a little less twitchy when you are steering small.

As far as I am aware all the top pros will setup their steering with full steering throw lock to lock.

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Old 10-23-2014, 06:11 AM   #486
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Originally Posted by Martin Crisp View Post
My personal view is that it is better to have complete steering throw (lock to lock) and learn how to drive with the additional steering it provides you. If your radio supports this, one thing you can do is add some negative steering exponential into your settings on your radio to make it a little less twitchy when you are steering small.

As far as I am aware all the top pros will setup their steering with full steering throw lock to lock.

Cheers
Just something I've learned in the past. A current X-ray car the max throw is 25-27 deg inside wheel. A serpent is a little ove 30 deg and I'm not sure about other cars. There will be a significant difference in steering feel if you run 30 or 25. I like 25-27 depending on the track and grip for an indoor carpet track. So basically what I saying is full lock can be different on different cars and if you're trying to tune a car at 30-35 deg you might have a rough task at hand vs one that only turns at 25 deg.
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Old 10-23-2014, 01:27 PM   #487
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Just something I've learned in the past. A current X-ray car the max throw is 25-27 deg inside wheel. A serpent is a little ove 30 deg and I'm not sure about other cars. There will be a significant difference in steering feel if you run 30 or 25. I like 25-27 depending on the track and grip for an indoor carpet track. So basically what I saying is full lock can be different on different cars and if you're trying to tune a car at 30-35 deg you might have a rough task at hand vs one that only turns at 25 deg.

An excellent point that different cars will have different "full lock" angles.

When I ran for xray I measured the inside tire angle at full lock and got 36.7 degrees. I am sure there is a margin of error in my measurement. I ran that car with full lock and liked it. When I ran for Top I measured the inside angle at 44.7 degrees and also ran that at full lock. What is interesting is that the top car always had less steering than the xray especially on asphalt even with having a greater inside tire max throw angle. The rear was that the ackerman was always greater in the top than the xray when both cars were set to their minimum ackerman. What is even more interesting is that the when the cars were set at minimum ackerman both cars had a 27.5 degree angle on the out wheel. So the bottom line is that what I have found more impactful is the amount of ackerman you run on the car than. i.e. with the same outside tire angles, the xray had more steering even with having less angle on the inside tire...i..e less ackerman. Now of course there are a lot of factors that affect steering, but i had done my best in setup, shocks and springs to equate the two cars as much as possible at the time.

So yes the amount of inside angle is important, but what is equally important is the amount of ackerman your car has.
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Old 10-25-2014, 10:52 AM   #488
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Hey Guys,

I released yesterday version 2.0 of my learnsetup.com app that has a new feature allowing discussion on a setup.

If you want someone else to be able to add comments on your setup, then you should have the "share with everyone" checkbox selected and click on the "update" button at the top. This makes the setup public so that others can provide comments on it...such as answering questions or providing suggestions.



After clicking on the "discuss this setup" button...you will see the comments made for this setup and button to be able to add comments




When you click on the "add comment" button in the above screen you will then see a text field where you add your comment and then tap on the green "save new comment" button.



So if you want someone to provide you with suggestions to your setup, make it public and then contact someone on rctech, facebook or whatever and ask them to provide a comment on it. I will be adding a feature to allow you to notify someone directly via learnsetup.com in the future, to make it easier to get someone to add comments to your setup, but you can just give them your name and they can search for your public setups and provide comments on it for now.

By the way, to search for someones setups go to the setups list page and at the top of the page there is a search field where you can enter a persons user id on learnsetup to see their setups.

As a reminder, to login to your learnsetup.com account, go to http://www.learnsetup.com and click on the login link on the upper right of the page.



Cheers.
Martin.
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Old 10-26-2014, 08:27 PM   #489
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Thanks for all your effort. I am signing up for a subscription tonight. I just finished reading the XXX main book.

I do have one question that maybe you could help provide clarity on.

I have been working under the assumption that lowering the roll center will produce more traction on that end of the car, due to more roll. For instance, the Xray setup book states that "more chassis roll equals more grip." I also believe that this is what is stated in the XXX main book.

However, I've been reading through your comments, and it seems that you suggest higher roll centers for the end of the car that you want to create more grip through a turn. For instance, "A higher rear roll center will give the rear more grip."

Could you help me understand what's going on and whether raising or lowering a roll center produces more grip through a turn.

Thank you
This is what's been confusing me for a while as well. I have Martin's Workbench app and it seems to disagree with my understanding and with my HUDY book. I, too, thought that lower roll center and thus more chassis roll would increase grip at that end of the car. Is that not the case?

On second thought, I think maybe a better understanding of lateral weight transfer is the root subject here. We all think of weight transfer as occurring when the chassis rolls, but I believe there is almost as much lateral weight transfer if the chassis doesn't roll as much... right? And if the chassis rolls then camber gain comes into play. But how do these tie together?
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Last edited by metalnut; 10-26-2014 at 08:42 PM.
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Old 10-26-2014, 10:05 PM   #490
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Martin, I've been searching for prices for Futuba 3pm and i've came up with these 2 with big diffrence on their price. the other one is listed with FASST system and the other one doesn't. this is the first one

http://www.ebay.com/itm/NEW-Futaba-3...item43ce9c0372

and here is the second one

http://www.rcmart.com/futaba-channel...ml?cPath=36_47

they have an 80$ difference. i'm not sure if they are basically the same or i need to buy the more expensive one? tyvm
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Old 10-26-2014, 11:56 PM   #491
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Martin, I've been searching for prices for Futuba 3pm and i've came up with these 2 with big diffrence on their price. the other one is listed with FASST system and the other one doesn't. this is the first one

http://www.ebay.com/itm/NEW-Futaba-3...item43ce9c0372

and here is the second one

http://www.rcmart.com/futaba-channel...ml?cPath=36_47

they have an 80$ difference. i'm not sure if they are basically the same or i need to buy the more expensive one? tyvm
The 3PM is a FASST transmitter: http://www.futaba-rc.com/systems/futk2021.html

The two links you provided are for the same radio. You're comparing prices from US companies to that of RCMart, who is overseas. RCMart is often much cheaper, you'll just have to pay for overseas shipping and wait a few weeks to get it.
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Old 10-27-2014, 12:23 PM   #492
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This is what's been confusing me for a while as well. I have Martin's Workbench app and it seems to disagree with my understanding and with my HUDY book. I, too, thought that lower roll center and thus more chassis roll would increase grip at that end of the car. Is that not the case?

On second thought, I think maybe a better understanding of lateral weight transfer is the root subject here. We all think of weight transfer as occurring when the chassis rolls, but I believe there is almost as much lateral weight transfer if the chassis doesn't roll as much... right? And if the chassis rolls then camber gain comes into play. But how do these tie together?
This is a very good question and one that I struggled with when I was learning about setup. For sure understanding weight transfer is a fundamental piece of understanding car setup and car dynamics.

First some quick definitions:

Just to be clear I am talking about dynamic weight transfer here. In other words it is not about adding physically more weight to a position on the car with weights. It is about how the existing cars weight is dynamically transferred from one or multiple tires to one or multiple tires as the car pitches and leans

Longitudinal weight transfer is the weight transfer from front to back under acceleration or back to front under braking.

Lateral Weight transfer is when you corner and weight is transferred from the inside wheels to the outside wheels.

Longitudinal Weight Transfer:

Lets talk about the more easily understood Longitudinal weight transfer first. As you dynamically transfer more weight to the front tires for example under braking, the front tires will have more grip than the rear tires because the front tires have more vertical load pushing the tires into the driving surface compared to the rear tires. This gives the front more grip than the rear. This is why when you get off the throttle in a corner the car steers more...because it is transferring more weight to the front tires. You can try this in your street car as well. Just drive into a long corner and then lift off the gas without changing your steering angle...the car will turn more.

So far so good,...and most people already I think understand longitudinal weight transfer.

Lateral Weight Transfer:

When your car is cornering the centripetal force acting on the car causes weight to be transferred to the outside tires from the inside tires. Your chassis setup will help control how much is transferred to the outside and also how much is transferred to the front or rear tires on the outside.

For example if you have 400grams of downward force on each of the 4 tires of your car when at rest, and you turn a right hand corner then you might end up with 600grams of downward force on the outside tires and 200grams of downward force on the inside tires assuming the chassis setup evenly distributes the weight between the front left and rear left and the car is going at a steedy speed.

So to answer the question, does this weight transfer of 400grams of downward force from the inside tires to the outside tires actually great more lateral grip in the corner than if we had actually transferred less weight from the inside tires to the outside tires. The short answer is no.

here is some content on the subject from my learnsetup.com app.

The important thing to remember about lateral weight transfer is, the greater the difference in load between the inside tire and the outside tire (i.e. more lateral weight transfer), the less overall lateral grip the car will have.

The reason for this is that as we increase the load on the tire by "X" amount, we don't get the same "X" amount increase in lateral grip. The curved orange line on the "Tire Performance Curve" shows that as you increase the vertical load on a tire by 100 grams, the tire does not produce the same incremental 100 grams of lateral grip.




So basically, the additional lateral grip created by downforce is not linear, it is a curve. And because it is a curve, as you transfer more weight to the outside tires from the inside tires you loose lateral grip.

....so now you are probably thinking....but wait, adding a stiffer swaybar in the rear of the car makes my car more loose because it takes away rear grip....but the car is flatter...so if it is flatter would it not transfer less weight to the outside tire and thus give more grip?.....

Well...that question always bothered me until I eventually figured it out with some research....lets see who knows the answer to that questions...why do stiffer swaybars reduce lateral grip......happy to answer in another post...

Cheers everyone..
Martin.
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Old 10-27-2014, 12:43 PM   #493
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I'll take a shot at this one.

Putting a stiffer swaybar on one end of the car will reduce lateral grip because you end up with less longitudinal weight transfer.
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Old 10-27-2014, 01:04 PM   #494
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I'll take a shot at this one.

Putting a stiffer swaybar on one end of the car will reduce lateral grip because you end up with less longitudinal weight transfer.
I think it's because the way sway bars work, you're actually picking the inside tire off of the ground while the outside tire is moving upward, so in addition to less lateral weight transfer (due to less body roll) you're also actually reducing the amount of vertical load on the inside tires.
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Old 10-27-2014, 01:21 PM   #495
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So if less lateral weight transfer means more grip, why are guys working so hard to create flex in their chassis?

I've been experimenting so far this year by getting my chassis to be stiff as possible (XRay T4 '14 with all screws in top deck, motor mount post and servo brace with top deck connection) and am finding I am driving much quicker than when I was trying to create flex like recommended to me.
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