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calculating FDR and rollout

calculating FDR and rollout

Old 08-06-2007, 11:19 AM
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Default calculating FDR and rollout

So I get FDR, and I use gearchart.com on a rgular basis, but I don't understand the difference between FDR and Rollout, could someone gimme a short explanation?
Also, what size are the Take-Off RP30's and CS27's, for calculating rollout?

TIA
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Old 08-06-2007, 11:22 AM
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Originally Posted by Blisster View Post
So I get FDR, and I use gearchart.com on a rgular basis, but I don't understand the difference between FDR and Rollout, could someone gimme a short explanation?
Also, what size are the Take-Off RP30's and CS27's, for calculating rollout?

TIA
i think they are 62-63mm
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Old 08-06-2007, 11:23 AM
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rp's and take0ffs are 63mm
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Old 08-06-2007, 11:25 AM
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rollout is how far your car travels in one tire rotation.
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Old 08-06-2007, 11:30 AM
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how far it rolls in one tire rotation? That would be the circumfrence of the tire.
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Old 08-06-2007, 11:44 AM
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One revolution of the motor/pinion=how far the car travels.


I think
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Old 08-06-2007, 11:47 AM
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ok, if im not mistake to calculate rollout, you mount the wheels on the chassis ans make a mark on the wheel. line up the wheel with the mark pointing down, then roll the car until the mark is back in that position. then measure the distance from where you sat the car to the distance it travelled to get the mark back to it's original position.
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Old 08-06-2007, 12:01 PM
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Roll out is how far the car travels for each rotation of the motor. Example - a Xray geared 31/116 with 56mm tires has a roll out of 27.64mm. Rollout will change as tires get smaller, and requires "gearing up" to maintain the same roll out.

FDR = spur / pinion X internal
Roll Out = tire diameter X 3.14 / FDR
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Old 08-06-2007, 12:36 PM
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Originally Posted by A. Rhodes View Post
Roll out is how far the car travels for each rotation of the motor. Example - a Xray geared 31/116 with 56mm tires has a roll out of 27.64mm. Rollout will change as tires get smaller, and requires "gearing up" to maintain the same roll out.

FDR = spur / pinion X internal
Roll Out = tire diameter X 3.14 / FDR

where do you get the 3.14 from is this a common number
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Old 08-06-2007, 12:52 PM
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Originally Posted by stuey View Post
where do you get the 3.14 from is this a common number
3.14 is pi ,pi is the constant ratio between the diameter of a circle and the circumference of that circle
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Old 08-06-2007, 01:04 PM
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rollouts helped me when I wasn't going as fast as the guys I was racing with who was running 19 turn. I found out that I wasn't geared the same because our rolouts were different. I use the gear wizard calc but you have to find out what your car final drive ratio is. You can usually get that from the manufacturerer. I was gearing my cyclone at 100 by 32 when the rollout showed I should be gearing at 100 by 38.

Once i found that out, I was just as fast as they were. make sure that you take the motor in consideration. when I gear my Komodo 19turn i use the 38 tooth pinion, but when I run checkpoints, I use a 42 tooth pinion because that motor likes to be geared higher than any other 19turn.

Rollout calculator is great but just make sure you keep an eye out on your motor as well as to not overgear it and burn the comm.
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Old 08-06-2007, 01:42 PM
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A. Rhodes - Thanks for the explanation, just what I was looking for!

Elboogie - Yeah, i ffigured that out when I switched to the Novak 13.5, I had to gear WAY up to get any speed out of my car (was geared at about 6.8 on my normal brushed motor, geared it up to a 4.5 with the brushless). I temp my motor after every run.
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Old 08-06-2007, 05:09 PM
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Elboogie - I have sent you PM's and you have not replied. Can you please get in touch.
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Old 08-07-2007, 05:52 PM
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I have an Excel sheet that work great if i could post it. Can someone tell me how?
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Old 08-08-2007, 12:03 AM
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Well I have a question


When looking at FDR's does a lower, say 4.50 ratio mean that the car would be faster with less torque to like 5.0, and vice versa?

So pretty much the smaller the numbers, the more speed?

Im getting all confused, I was recomended a ratio between 4.50 and 5.0 and im looking at a FDR sheet from gear chart, and im looking to see which spur will work best with the pinions I have, to get the ratios I want
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