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Old 10-18-2006, 05:06 PM   #1
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Default Roll-out

How exactly do you figure out what the best roll-out to use on a track is. I know each track might be different, but I don't know how to determine what is the best roll-out. Any help would be greatly appreciated.
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Old 10-18-2006, 05:10 PM   #2
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I have this doubt too....
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Old 10-18-2006, 06:11 PM   #3
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I believe rollout is basiclly used when you run foam tires. Someone will eventually post the whole formula. I use rubber tires so don't really determine rollout.
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Old 10-18-2006, 06:16 PM   #4
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the formula for rollout is as follows:

(tire diameter X pi) / [(spur/pinion) X the internal ratio of the tranny.]

do the whats in the parenthesis first.

and for the all elusive rollout, go for when the motor winds out approx. 2/3 down the straight.

-Zac
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Old 10-18-2006, 06:19 PM   #5
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Can the same formula be applied to rubber tires? If not what is the correct method?

Naut
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Old 10-18-2006, 06:22 PM   #6
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Quote:
Originally Posted by Nautilian
Can the same formula be applied to rubber tires? If not what is the correct method?

Naut
you could but you only need to do this when you are comparing rollout w/ a foam tire guy.

rubber tire guys compare the FDR of the car b/c the rubber tires are relatively the same size. to find the FDR of your car, use only the bottom of the formula.

-Zac
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Old 10-18-2006, 08:59 PM   #7
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OK here it is...

http://www.gearchart.com/index.cfm?f...n=chart.create

Rollout is the distance that the car moves forwards, per revolution of the motor.

due to different tyre sizes, internal ratios, spurs and pinions this is the best way to compare gearing.

for a silver can I use a rollout of 40mm for a tight track, upto 50mm for a large track.

for a stock motor, between 25 and 35

for mod, im guessing between 15 to 25

the best way is to just experiment and ask the fast guys what rollout they are running...

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Old 10-19-2006, 04:58 AM   #8
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Quote:
Originally Posted by Z.Hallett
you could but you only need to do this when you are comparing rollout w/ a foam tire guy.

rubber tire guys compare the FDR of the car b/c the rubber tires are relatively the same size. to find the FDR of your car, use only the bottom of the formula.
Understood however I am more interested in using the rollout for accuracy in setting up my gear ratios to the motor.

At the sametime, I know roughly where the ratio should sit when using the formula that uses the tire diameter, however where can I find an accurate discription regarding just the bottom formula, as I would like to find a guideline to my setup! 6.435 means nothing to me other than a ratio, I would like to put this into relation to something.

Thanks a mil
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Old 10-19-2006, 10:35 AM   #9
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On a direct drive car (like a 12th scale) use the following:

MMPR (MilliMeters Per Revolution, It's how far the car will travel in mm when the motor makes one revolution)

W= Wheel diameter in mm

S= Spur gear teeth (ex: 96T spur)

P= Pinion teeth (ex: 25T pinion)

MMPR= (P/S)*(3.1416*W)

Example: My 12th scale has a monster Pro and 39 MMPR is a good rollout for that motor. What Pinion do I use??
I measure, W=46mm, My spur is 96.

P=(MMPR*S)/(3.1416*W)
P=(39*96)/(3.1416*46)
P=25.9
Round it off to P=26T

So slap in a 26T pinion and it's go time!!

For cars with internal drive ratios (Like a TC3, it has an internal drive ration of 2.5:1) Check your user manual for the drive ratio and add it to the above equation like so:

DR=Drive ratio (Ex: DR=2.5 for a TC3)

MMPR= (1/DR)*(P/S)*(3.1416*W)

Example: I'm running a 19T spec motor in my TC3, what pinion do I use. Guys at the track say that 25 MMPR is a good start.
I measue, W=65mm (full size TC tire), My spur is 100T

P=(MMPR*DR*S)/(3.1416*W)
P=(25*2.5*100)/(3.1416*65)
P=30.6
Round it off to 30T or 31T

Select the 30T or the 31T and try it out.


This equation can be applied to any car, a AE B4 has a 2.6:1 drive ratio so just apply it as above.

Hope this helps.
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Old 10-19-2006, 11:25 AM   #10
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That makes a lot of sense!

Thanks for that!

I was told the following are the best recommended rollout ratios:

ROAR Stock 30.99 to 34.38
17T - 31.08 to 31.86
16T - 29.47 to 30.30
15T - 27.86 to 28.68
14T - 27.08
13T - 26.28
12T - 25.53
11T - 24.69
10T - 23.88
9T - 23.10

Any input about those values?

Naut
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Old 10-19-2006, 12:42 PM   #11
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Quote:
Originally Posted by Nautilian
That makes a lot of sense!

Thanks for that!

I was told the following are the best recommended rollout ratios:

ROAR Stock 30.99 to 34.38
17T - 31.08 to 31.86
16T - 29.47 to 30.30
15T - 27.86 to 28.68
14T - 27.08
13T - 26.28
12T - 25.53
11T - 24.69
10T - 23.88
9T - 23.10

Any input about those values?

Naut

Those are ball park figures, but they will vary significantly depending on the size of the track, type of car, type of surface.

Best bet would be to ask the fast guy at your track what his rollout is, start by running two teeth lower than his to get a feel for the track and your setup (and so you don't smash your car to bits). If your making consistent laps and your motor is not hot, up your rollout a bit, run some packs and get the feel. Good luck
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Old 10-19-2006, 12:57 PM   #12
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When you up your rollout, do you get further or closer to 0?

I have a Tamiya Super Stock TZ and was thinking at starting with a 33.5 rollout, people here in South Africa are not very clued up when it comes to RC . So is that a good starting off point?

Also what is the ideal running temp of a motor? What temp should you be hitting when you know you are around the sweet spot of the gear ratio?

Sorry about so many questions... I am a n00b.

Naut

Last edited by Nautilian; 10-19-2006 at 01:08 PM.
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Old 10-19-2006, 02:14 PM   #13
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What kind of car do you have? What type of surface are you running on? Rubber of Foam tires? What kind of batteries are you using?
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Old 10-19-2006, 02:20 PM   #14
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-EVO 5 & TRF 415MSX
-Surface is tar with medium -> high traction
-Tamiya rubber B3 tires with medium inserts
-GP 4300mA batteries.
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Old 10-19-2006, 02:31 PM   #15
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Quote:
Originally Posted by Nautilian
When you up your rollout, do you get further or closer to 0?
do you mean the bottom of the formula?

Quote:
Originally Posted by Nautilian
Also what is the ideal running temp of a motor? What temp should you be hitting when you know you are around the sweet spot of the gear ratio?
i dont worry about what my motor temp. is as long as its not burning brushes, the tag on the arm doesnt turn black/brown, the comm didnt turn orang-ish, or smoke didnt pour out.

-Zac
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