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Old 10-04-2005, 11:27 PM   #1
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Default How important is free Spin?!

I have a Mi2 and even though I think the drivetrain is fairly free it doesn't free spin as well as my friends JRX-S, and no where near another friends shaft car. Question is how important is free spin in the cars performance?
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Old 10-04-2005, 11:37 PM   #2
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In stock and silver can racing free spin is (IMO)very important because we run high gearing (4.2 silvercan) and the slightest drag in the drivetrain is noticeable in slower acceleration and top end.

Not so important in mod tho it pays to make your drivetrain as free as possible in any grade.
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Old 10-04-2005, 11:37 PM   #3
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Very. The amount of time the drivetrain spins for can often be misleading. A drivetrain that spins longer can just mean that it has more MOI and doesn't necessarily mean it's more "efficient."
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Old 10-04-2005, 11:41 PM   #4
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Originally Posted by Goonish
Very. The amount of time the drivetrain spins for can often be misleading. A drivetrain that spins longer can just mean that it has more MOI and doesn't necessarily mean it's more "efficient."
Yeah which is why shafts spin the way they do.
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Old 10-05-2005, 04:59 AM   #5
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While we're talking about freespin, is it possible that shaft drives spin longer because they have no static tension, like the tightness of a belt? The gears float (mesh) between each other when the car is moving.

Also, has anybody weighed the drivetrain components of SD's and BD's? Not saying that Rkeasler is wrong about SD weighing more, but with aluminium inputs and a carbon fiber shaft, I wouldn't be suprised if they weigh about the same, maybe a little more for the SD. Maybe not enough to create such a high inertial force once freespinning.
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Old 10-05-2005, 11:53 AM   #6
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well I will tell you this. I had a MI2 for a few years and it would routinely out accelerate TC3's. I now have a BMITC4 with ceramics and it feels about the same on the track. When I spin the tc4 it spins forever but that does not translate to acceleration on the track. This is just from first hand experience. In general though, you can never be too free
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Old 10-05-2005, 12:03 PM   #7
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Case in point is the TA05.. the most free drivetrain i've ever known on a belt car, and takes off in a heartbeat from the lack of drag.

It takes no effort to move the belts by hand, but won't freely 'run' for 20 seconds on its own just because there's no mass in the belts and pulleys to keep the inertia going.
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Old 10-05-2005, 12:56 PM   #8
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A heavy drive train would spin longer because of the flywheel effect. Having a drive train be able to spin for 5 minutes means nothing. As long as there's nothing binding up the drive train and it's nice and smooth, you're fine.
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Old 10-05-2005, 01:46 PM   #9
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Quote:
Originally Posted by Jon Kerr
A heavy drive train would spin longer because of the flywheel effect. Having a drive train be able to spin for 5 minutes means nothing. As long as there's nothing binding up the drive train and it's nice and smooth, you're fine.
Hey Jon hows it going, my car is very free but you can tell the weight of the drivetrain parts are not the same as say a JRXS so what you said makes me feel better. I ran my fastest lap and most total laps with my friends Losi this past weekend but I'm not so sure it was the car, it seemed that his setup steered so much better than mine. So now I am going back to the drawing board to get my Mi2 to steer alot more. I have suffered from a off power push for a while but may have it figured out. Will I have a problem with running my stock shocks with Schuie Pro-springs, everyone seems to run TRF shocks and I don't want to do that unless that is the only way to get the car the way I want it. I am going to stick with this car until the EC is out unless i just can't get it right. Are you going to be a the Nats hadn't seen your name at practice yet and I couldn't get off to go

Rod
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Old 10-05-2005, 01:50 PM   #10
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No nats for me. Vegas took it's place I'll PM you with some info.
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Old 10-05-2005, 02:13 PM   #11
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In gereral, free spin or minimum drag is always good.....however, compare from shaft and belt, that is just difficult to prove FREE SPIN = faster or better...

I look at my Pro 4 as an example..........no belt car can spin like that or TC4 (about 8-10 second of free spinning with no pinion mounted...) however does not make the Pro 4 any faster or any advantage (from free spinning) then any belt car like FK05 or RDX.....

Again, in gereral, free spin is a good thing, just not compare shaft vs belt, 2 different things.
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Old 10-06-2005, 03:47 AM   #12
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Having free spin car I think is good thing, just like engine cars.

Sometime ago, I have wild idea to use one way bearing front and rear for xray t1fk, but my friend oppose the idea telling me to check with car setup instead of being hardcore . I should remind you the brake is gone when you use two one way bearing. In my case I don't use brake at all.
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Old 10-13-2005, 08:23 AM   #13
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Some of you are onto the right idea about the mass of the drive train. Somebody used the term MOI? Momement of inertia? The majority of the MOI in a 4WD sedan is in the tires (the rubber), not the shaft or the belt. Shaft drives inherently spin "freely" while belts seem to have a bit more drag force. The question is does it matter? Probably more so in stock. How much? Not much. What's more important is how does the chassis handle.

My 3800 lbs Transam has great coast down, does that mean it's a fast car? Not really.
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Old 10-13-2005, 12:45 PM   #14
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When you are freespinning your car, the drivetrain is inthe relaxed state....which is perfect..if you're trying to make a cub-scout rally car....

In the real world your drivetrain is loaded and it's about efficient power transfer...

Knowing how your car spins..and checking components individually is a nice way to free up any drag...but comparisons from car to car really don't carry much weight...
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Old 10-13-2005, 02:55 PM   #15
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Yes, free spin is very very important. It's the most important to do in the RC racing world. Do bother and take hours to set your car for the longest spin in your pit table than practicing with other guys on track (www.bad_ideas.com)
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