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Old 11-07-2008, 01:47 PM   #1
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Default Fk 05 17.5 gearing

I have an xray fk 05 that I am putting a 17.5 novak brushless system in. I am running 60 MM tires We run a 90 X 48 track with a straightaway the entire length. acording to the novak site i need a rollout of 3.5 but that looks like it is going to be pretty tough. I would need to run like a 78 spur with a 62 pinion. Can anyone confirm this for me?
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Old 11-07-2008, 03:22 PM   #2
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No, Novak lists a FDR of 3.5. You'd be looking at a rollout around 1.9 to 2.1 inches with a Novak 17.5. Not sure what the internal drive ratio is on the FK05, but if it is the same as a T2 007 (1.7 ratio 34/20 pulleys), if you are running a 96 tooth spur, with 60mm tires, you'd need around 38 - 43 tooth pinions.


Cribbed From the XRAY forums

Calculating Rollout

1. Determine the Drive Train Ratio (DTR) - The ratio of all the internal gears from the transmission, including differentials and pulleys is known as the drive train ratio. The drive train ratio is usually different for each model of car. Your owner’s manual should provide this information, but keep in mind that some manufacturers use the words "transmission reduction" or "internal reduction" to indicate the DTR. The DTR in most cases cannot be changed, unless you are able to change the number of teeth on the pulleys and/or gears. My original T1 has the Xray low ratio pulley set which provides a DTR of 1.77.

2. Determine the Primary Drive Ratio (PDR) - The ratio between the pinion and spur gear is known as the primary drive ratio. This number is commonly rounded up to the nearest thousandth after the decimal point.

Spur / Pinion = PDR

My cars PDR: 93 / 24 = 3.875

3. Determine the Final Drive Ratio (FDR) - The ratio between the DTR and the PDR is known as the final drive ratio. This number is commonly rounded up to the nearest thousandth after the decimal point.

PDR x DTR = FDR

My cars FDR: 3.875 x 1.77 = 6.859

4. Determine the Rollout - Rollout is not affected by the motor, batteries, or electric components you are using. Rollout simply defines how all of the gears, belts/shafts and tires work together to make the car accelerate and reach top speed. Rollout is affected by your tires diameter, but don’t ever let anyone tell you that rollout only matters if you run foam tires. Rollout is calculated using tire diameter and therefore the diameter of both foam and rubber tires make a difference since both wear down. However, the diameter is more important if you run foam tires since they can be used anywhere from 64mm to 55mm. And as they wear and get smaller, your rollout value will change a lot more. Rubber tires do not wear down near as fast or as much so the change will be much less. The circumference is commonly rounded up to the nearest hundredth after the decimal point. The rollout is commonly rounded up to the nearest thousandth after the decimal point for American standard and to the nearest tenth after the decimal point for metric. My car has Take Off CS32 rubber tires with a diameter of 2.4375 inches (62 millimeters, although it’s common to find that other drivers use 63mm for a rubber tire diameter).

Tire Diameter X 3.14 (value of PI) = Tire Circumference

Tire Circumference / FDR = Rollout

My cars tire circumference: 2.4375 x 3.14 = 7.65 inches (or 194.68 millimeters)

My cars standard rollout: 7.65 / 6.859 = 1.115
* The car travels 1.115 inches for each revolution of the motor shaft
Or metric rollout: 194.68 / 6.859 = 28.4
* The car travels 28.4 millimeters for each revolution of the motor shaft
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Old 11-07-2008, 04:18 PM   #3
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Default gearing

What am I missing? The internal drive ratio is 1.7 like you thought. 3.5 inches converted to mm is 88.9. Using Gearchart.com and the numbers that you gave me (96 spur and 40 pinion) it comes out to 46.2 mm. That converted to inches is 1.82. What am I doing wrong?
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Old 11-07-2008, 05:32 PM   #4
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Quote:
Originally Posted by sheetmetal2 View Post
What am I missing? The internal drive ratio is 1.7 like you thought. 3.5 inches converted to mm is 88.9. Using Gearchart.com and the numbers that you gave me (96 spur and 40 pinion) it comes out to 46.2 mm. That converted to inches is 1.82. What am I doing wrong?
Novak recommends FDR = 3.5

PDR x DTR = FDR

See the attached zip file, which contains an Excel spreadsheet for Xray Rollouts. If you need to change the spur, change the value in Cell O1 and press enter. The top chart is rollouts in mm, the bottom chart is rollouts in inches. The top row for each chart is wheel diameter, and the left column is the pinion tooth count. To find a desired rollout, start with the tire diameter, go down the column until you find the rollout you want, then find the pinion you need for that rollout.

So for the desired rollout of 1.82 inches, a 60mm tire gives you a 40 tooth pinion. Note that the columns are the same tire diameter across both charts (60mm = 2.36 inches)
Attached Files
File Type: zip T2Rollout96Spur.zip (20.3 KB, 23 views)
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Old 11-07-2008, 09:29 PM   #5
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Default gearing

I'm not able to open your file. But I am trying to understand what I am trying to do to make this gearing work. Where am I going wrong using the inches to MM conversion and gearchart.com?
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Old 11-07-2008, 10:18 PM   #6
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Originally Posted by sheetmetal2 View Post
I have an xray fk 05 that I am putting a 17.5 novak brushless system in. I am running 60 MM tires We run a 90 X 48 track with a straightaway the entire length. acording to the novak site i need a rollout of 3.5 but that looks like it is going to be pretty tough. I would need to run like a 78 spur with a 62 pinion. Can anyone confirm this for me?
Thanks,
Chris
Hi
I have the TF05 rubber tires and my spur is 102 and my pinion 49T= 3.5 FDR
Now for 60mm foam tire with the same 3.5 FDR you need 40T pinion
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Old 11-08-2008, 07:13 AM   #7
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Originally Posted by sheetmetal2 View Post
I'm not able to open your file. But I am trying to understand what I am trying to do to make this gearing work. Where am I going wrong using the inches to MM conversion and gearchart.com?
Your confusing the final drive ratio of the car (spur*internal ratio/pinion) for the rollout of the car. You dont need the tire size to calculate the FDR of the car. An FDR of 3.5(96/45 gearing), used in combination with your 60mm tires equates to a rollout of 53mm, or 2.08 inches.

Final drive chart:FK05 FDR chart

Rollout chart: FK05 rollout chart
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Old 11-08-2008, 07:58 AM   #8
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Thank you all for you help. I knew that I had to be getting something confused. That 78 tooth spur with a 58 tooth pinion wasn't going to work!!
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Old 11-08-2008, 12:02 PM   #9
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For a 17.5 I use a 88t spur.

For a 13.5 I use a 100t spur.

I follow the other guys at the track for rollout as Novak has the rollout to low for racing 5 minute heats.

I have the BMI Chassis which allows the motor mount to move front and back so I am not 100% sure these will work in your car. For my trans-am I am running 27t and standard chassis but have not run brushless in the Xray chassis.
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Old 11-08-2008, 04:21 PM   #10
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Default gearing

That is the same chassis that I use. What roll out works good for you? Pinion? Tire size?
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Old 11-08-2008, 07:18 PM   #11
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To run the 17.5 you will need to grind the motor mount a hair. A dremmel sand paper drum to off the extra aluminum.
Attached Files
File Type: pdf 13.5.pdf (345.7 KB, 122 views)
File Type: pdf Fk05 17.5.pdf (347.2 KB, 144 views)
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Old 11-08-2008, 07:35 PM   #12
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Default motor mount

What part of the motor mount do you need to grind? The motor mount holes? To run what pinion the 46?
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Old 11-08-2008, 08:56 PM   #13
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Quote:
Originally Posted by sheetmetal2 View Post
What part of the motor mount do you need to grind? The motor mount holes? To run what pinion the 46?
Right where to motor touches the mount. You can not get the motor close enough the spur gear do to using a 88t spur to get the correct rollout.

Also with the BMI you can use the readily available Kimbrough/Associated spur gears they do not rub on the mount as with the xray chassis.
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Old 11-09-2008, 08:30 AM   #14
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Are you talking about the motor mount or the Rear bulkhead? I noticed that I cann't get all the travel out of my motor slide screws both chassis and motor due to the motor touching the bulkhead.
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Old 11-09-2008, 04:39 PM   #15
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Quote:
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Are you talking about the motor mount or the Rear bulkhead? I noticed that I cann't get all the travel out of my motor slide screws both chassis and motor due to the motor touching the bulkhead.
My fault bulkhead not motor mount. Also if you have the motor protector use as small a screw and nut as you have so the motor does not get hung up on the screw of nut.
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