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Old 05-10-2011, 09:05 AM   #1
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Default Track size, FDR, spur , pinion Boost and turbo...MOD TC questions

Ok here the deal I have decided to run Mod TC (Xray T3 (1.9 internal drive) at my local track with a Duo3 6 turn and tekin RS pro speed controller. I really should be running 17.5 but Mod is the only class this year. The track is relatively large (200' straight) and 1/8 scales generally negotiate it in about 14 seconds. There is a large sweeper a killer crosstown and a few turns to work out your setup...I actually love the track.
My question are:

How do you determine your FDR?

Is FDR track dependent?

Is a lower FDR translate into torque and hi FDR translate to top end?

Whats the difference achieving a 6.5 FDR with a 118 spur pinion combination vs a 110 spur pinion combination?

Which combination is more efficient?

When to boost?

When to turbo?

boost vs turbo?

I do understand that everything is dependent I just wanted to hear what everyone else thinks.

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Old 05-10-2011, 10:49 AM   #2
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Join Date: Apr 2011
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I posted the almost exact question in the rookie section earlier ;-)...

spur and pinion size question

With regards to the FDR question the equation would look like this:


F.EX. my T2'008 has an internal ratio of 1.7 so the equation with a 84tooth spur and a 34 tooth pinion would be:

84 / 34 * 1.7 = 4.199

You could of course work backwards to figure out your ratio between spur and pinion.

Say your max FDR is 3.500, like is it for me, you would get an equation like this:

SPUR / PINION * 1.7 = 3.500

some math....

SPUR / PINION = 3.500 / 1.7

more math...

The ratio between spur and pinion would be:

SPUR / PINION = 2.058

Meaning that your spur should be 2.058 times bigger than your pinion...


As for the rest of your question I'm my self at a loss ;-)
Xray T2'008 - Robitronic 13.5 Turn Brushless - Excelorin ESC
Losi XXX-S - Traxxas (550 can) 12 Turn Brushed - GM V3r ECS
Traxxas Rustler - Arrowind 13 Turn Brushless - Arrowind ESC
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Old 05-10-2011, 11:03 PM   #3
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Sorry only have answer for few of your questions. FDR very depend on the track and motor. But generally for our track with around 50M straigth for 4.5T (turbo) we run anything from 8.5-9 depend on the layout. In the old brushed days a large spur with same gear ratio usually give a little better top speed than smaller spur. But with the lipo and brushless now day I really don't notice any different..... But I still like to run larger spur as it last longer. lol smaller FDR means more top speed but less punch off the line. For turbo as every driver have different driving style most people set it up differently.... I guess the main thing is on the striaght the motor reach max rpm around 1/3 or so down the straight so you don't over-rev the motor, and set it up so you won't over shot the corners at in field..... My 2 cents.
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