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Old 10-14-2008, 11:31 AM   #2701
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Questions?? 21.5 Lipo FDR question

Hey everyone,
I am running into a bit of confusion on what FDR's are allowed for the
21.5 Novak Brushless & Lipo setup. The TransAm website rules state that the
Lower limit is a 4.2FDR...
I have read on other sites (hence the confusion) 3.99 - 9.99 FDR...
Can anyone clarify the acceptable FDR's for this combo?
And would anyone be willing to offer a couple of suggested FDR's for the
Associated TC5R? My thoughts were running around a 5.5 FDR Maybe?
Thanks for any/all assistance!
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Old 10-14-2008, 11:36 AM   #2702
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The ONLY USVTA-approved legal limit for FDR limits at this point for the 21.5/LiPo combo is 4.2. That means a 4.19 is not legal.

I'd be curious as to where you saw 'other' FDRs listed.
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Old 10-14-2008, 11:47 AM   #2703
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Quote:
Originally Posted by ApexSpeed View Post
The ONLY USVTA-approved legal limit for FDR limits at this point for the 21.5/LiPo combo is 4.2. That means a 4.19 is not legal.
Seconded.
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Last edited by liljohn1064; 10-14-2008 at 01:54 PM.
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Old 10-14-2008, 11:51 AM   #2704
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Quote:
Originally Posted by ApexSpeed View Post
The ONLY USVTA-approved legal limit for FDR limits at this point for the 21.5/LiPo combo is 4.2. That means a 4.19 is not legal.

I'd be curious as to where you saw 'other' FDRs listed.
OK, I'm confused....
the rules say: Final drive ratio is to not exceed 4.2. Motor timing advance is allowed.

But the suggested FDR for 21.5 is 21.5 brushless/LiPo: 4.2 - 4.3 FDR

And now 4.19 is not legal?

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Old 10-14-2008, 11:57 AM   #2705
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Quote:
Originally Posted by Nova F1 Racer View Post
OK, I'm confused....
the rules say: Final drive ratio is to not exceed 4.2. Motor timing advance is allowed.

But the suggested FDR for 21.5 is 21.5 brushless/LiPo: 4.2 - 4.3 FDR

And now 4.19 is not legal?

Yes, it's a little confusing -- "not to exceed" means "not to be numerically lower than". A lower number means a faster car on the top end, so a lower number is higher than a higher number...
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Old 10-14-2008, 11:58 AM   #2706
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Quote:
I'd be curious as to where you saw 'other' FDRs listed.
Here are the 2 weblinks I found from Google...

http://www.rctrack.com/racing/2008/T....5%20motor.htm

http://www.rctrack.com/racing/2008/T...21%20April.htm

These look like local track rules, but they still add to the confusion.
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Old 10-14-2008, 12:03 PM   #2707
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Quote:
Originally Posted by Gyro View Post
Here are the 2 weblinks I found from Google...

http://www.rctrack.com/racing/2008/T....5%20motor.htm

http://www.rctrack.com/racing/2008/T...21%20April.htm

These look like local track rules, but they still add to the confusion.
Those look old, and they do state that the FDR limit may be changed "in the future", which already happened. They also allow the Crawler motor, which USVTA does not.
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Old 10-14-2008, 12:36 PM   #2708
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Quote:
Originally Posted by Gyro View Post
Hey everyone,
I am running into a bit of confusion on what FDR's are allowed for the
21.5 Novak Brushless & Lipo setup. The TransAm website rules state that the
Lower limit is a 4.2FDR...
I have read on other sites (hence the confusion) 3.99 - 9.99 FDR...
Can anyone clarify the acceptable FDR's for this combo?
And would anyone be willing to offer a couple of suggested FDR's for the
Associated TC5R? My thoughts were running around a 5.5 FDR Maybe?
Thanks for any/all assistance!
Quote:
Originally Posted by liljohn1064 View Post
Seconded.
Quote:
Originally Posted by Nova F1 Racer View Post
OK, I'm confused....
the rules say: Final drive ratio is to not exceed 4.2. Motor timing advance is allowed.

But the suggested FDR for 21.5 is 21.5 brushless/LiPo: 4.2 - 4.3 FDR

And now 4.19 is not legal?

Quote:
Originally Posted by reenmachine View Post
Yes, it's a little confusing -- "not to exceed" means "not to be numerically lower than". A lower number means a faster car on the top end, so a lower number is higher than a higher number...
OK... that really made sense.... NOT!!!

I thought this was a simple class to run....
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Old 10-14-2008, 12:44 PM   #2709
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Quote:
Originally Posted by Nova F1 Racer View Post
OK... that really made sense.... NOT!!!

I thought this was a simple class to run....
Yeah, gearing is always the weird thing to learn or teach. We run a spec silver can class, and with the silver can gearing is pretty much everything. It's sometimes a challenge to teach the new guys about FDR and spur/pinion combos, but once you get it, you're good to go.
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Old 10-14-2008, 12:55 PM   #2710
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Ok as I read all of the info, here are my deductions... Please correct me if I am wrong.

Novak SS Brushless 21.5 & Lipo combo acceptable FDRs are:

4.2 thru 9.99 Correct?

If that is true then based on this quote from 414Mph's post from the previous page...
Quote:
Get a Novak 21.5 motor and don't look back. As long as you can achieve mid 5.x gearing with your chassis, you will have the time of your life with the reduced motor maintanance and battery managment. This package is competitive.
Would a 5.5 FDR:
A. Be USVTA Legal?
B. Be a suitable FDR to "Try" in practice on my TC5R?

I am only asking as I want to stay 100% within the USVTA rules.
Better racing through Integrity

Thanks again for all the info!
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Old 10-14-2008, 01:13 PM   #2711
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Quote:
Originally Posted by Gyro View Post
Ok as I read all of the info, here are my deductions... Please correct me if I am wrong.

Novak SS Brushless 21.5 & Lipo combo acceptable FDRs are:

4.2 thru 9.99 Correct?

If that is true then based on this quote from 414Mph's post from the previous page...


Would a 5.5 FDR:
A. Be USVTA Legal?
B. Be a suitable FDR to "Try" in practice on my TC5R?

I am only asking as I want to stay 100% within the USVTA rules.
Better racing through Integrity

Thanks again for all the info!
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A. Yes, 5.5 would be legal as it's numerically higher than 4.20.

B. I'm not sure it's an appropriate FDR, but I don't run 21.5 so I can't say. If I did, I'd be more inclined to start with the recommended FDRs on the USVTA site. It depends on your track though -- if it's really tight and technical then 5.5 may be great. It's harmless to try as worst case you'll just be slow and your motor will be nice and cool.
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Old 10-14-2008, 01:15 PM   #2712
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FDR is fun.

In these rules, by increasing your pinion size, you actually increase top speed and decrease acceleration. What's being limited is your actual top end speed by not being able to go lower than a 4.2 FDR. Its like putting a governor on your motor to only allow so much usable power at max RPMs for the armature. A lower FDR on a 21.5 AND everyone else would get their butts handed to them on the straights.

The opposite is true for FDRs over 4.3. A higher FDR and everyone else would get their butts handed to them in the corners.
(this ratio is within the rules and is just an example)
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Last edited by liljohn1064; 10-14-2008 at 01:46 PM. Reason: explanation
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Old 10-14-2008, 01:16 PM   #2713
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Yes. Um A.
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Old 10-14-2008, 01:22 PM   #2714
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from the VTA Rules page:

Motor Specifications:
Option 1: 27-turn ROAR stock motor: No FDR limit, bearings are not allowed.

Option 2: 17.5 brushless: Motor timing advance is allowed. 12.5 mm rotor diameter maximum (no "tuning" rotors are allowed).

Option 3: 21.5 brushless with 2C LiPo: Novak SS21.5 Pro brushless motor (pn:3421) ONLY combined with any ROAR-approved hard-cased 2C 7.4v LiPo pack up to and including 5000 mAh capacity. Novak motor is the ONLY motor allowed at this time, because there are no ROAR mandates or restrictions for the 21.5 brushless motors. All house track rules regarding LiPo usage apply. Final drive ratio is to not exceed 4.2. Motor timing advance is allowed. 12.5 mm rotor diameter maximum (no "tuning" rotors are allowed).

Suggested gearing FDR recommendations:

* 27t brushed/4-cell: 5.4 - 5.7 FDR
* 17.5 brushless/4-cell: 3.5 - 3.7 FDR
* 21.5 brushless/LiPo: 4.2 - 4.3 FDR

Tracks should not dictate which motor combination a racer should choose. All three motor/battery combos have been tested to compete evenly against one another in competition with great success. If any one power choice shows a definitive advantage at a certain track, it is up to the race managment to even the racing out via suggested gearing changes.
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Old 10-14-2008, 01:30 PM   #2715
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Okie, I didn't think this was such a confusing issue, but apparently is it.

There is a difference between a "suggested" gear ratio and the limited ceiling in the rules. You can run ANY ratio you want with the 21.5, as long as it is not a lower numerical number than 4.2. So technically, a 4.199999 FDR would not be allowed, not that you could really get that number in gears.

The USVTA suggested gearing is the number that the 21.5 seems to perform best on most tracks with LiPos, but YMMV. I'm not sure where Marty got his 5.XXX suggestion, but you will need to be down around 4.2 through 4.4 to be in the ballpark.

Simple. Don't over-complicate things by thinking too hard.
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