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New Dragster - 7/4/2007 5:52:51 PM   
cork44


 

Posts: 62
Joined: 7/30/2006
From: Schererville, IN, USA
Status: offline 		Hi, I just got a new to me dragster, it is super fast and I am trying to make improvevments in it. How do I calculate the potential top speed with my gearing? Its a single speed and the gears are 130t and 20t. I figure the engine is around 40,000rpm, and the tires are the standard 3.25" nitro dragster tires. What is the formula for top speed? Thanks
       Post #: 1

RE: New Dragster - 7/4/2007 6:25:32 PM   
Nick2618



Posts: 3656
Joined: 3/15/2007
From: Sarasota, FL, USA
Status: offline 		This page has some info on gear ratios and caculating top speed. Not sure if its only for electric though... Anyways check it out.

http://www.rcuniverse.com/forum/m_3255405/tm.htm

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RE: New Dragster - 7/4/2007 7:32:52 PM   
cork44


 

Posts: 62
Joined: 7/30/2006
From: Schererville, IN, USA
Status: offline 		HI so if i do the math right, I have a 130t spur gear and 20t pinion gear and my tire diameter is 10.25". I come out with a top speed of 161MPH at 40,000rpm. Sounds good in theory doesn't it? I'd settle for half of that!

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       Post #: 3

RE: New Dragster - 7/4/2007 8:18:51 PM   
ac hauswald


 

Posts: 146
Joined: 3/13/2004
From: Houston, TX, USA
Status: offline 		Hi cork44 and welcome to the wild world of RC drag racing. Yea, 161mph would be pretty good if you can get there.

When we did the math on your set up, we came up with 58mph. Here's the formula we've been using for the R2E:

MPH = 0.0029 x Tire Size (diameter in inches) / Gear Ratio x RPM

Our rail is running belt drive at 2.00:1 transmission ratio, with a PGR of 3.11. Our O/A GR is 6.22, so pretty close to your O/A of 6.25. We are running TM Racing Tires with 3.25" diam and and RAE NEO2 motor turning 40,000rpm. We ran a best of 60.8mph during timing runs and a best of 57.7mph during eliminations last weekend, so that sort of validates the above formula.

Could be you're plugging in your tire circumference at 10.25" instead of your tire diameter at 3.25". Anyway, keep working at it and let us know what you come up with.

Hey nick2618 - thanks for the link. We were using a FASTMATH RC Calculator on another website; but it went away. This in-house link is a great substitute.

//AC//


< Message edited by AHR43 -- 7/4/2007 8:23:41 PM >

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RE: New Dragster - 7/4/2007 9:03:00 PM   
cork44


 

Posts: 62
Joined: 7/30/2006
From: Schererville, IN, USA
Status: offline 		Well I knew it wouldn't go 161MPH, but I was hoping for more than 58MPH. I did put in the 10.25" for the circumference. I'll have to bring it to the track to get a time, but it sure looks faster than that. Thanks

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       Post #: 5

RE: New Dragster - 7/4/2007 9:21:32 PM   
cork44


 

Posts: 62
Joined: 7/30/2006
From: Schererville, IN, USA
Status: offline 		What is the final draive ratio? is it Transmission ratio, or pinion:spur ratio, or rollout ratio?

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       Post #: 6

RE: New Dragster - 7/4/2007 11:07:26 PM   
ac hauswald


 

Posts: 146
Joined: 3/13/2004
From: Houston, TX, USA
Status: offline
quote:

ORIGINAL: cork44

What is the final draive ratio? is it Transmission ratio, or pinion:spur ratio, or rollout ratio?


Hi cork44,

Final Drive Ration = 130/20 = 6.5

Spur / Pinion = FDR (Final Drive Ratio). Your PGR (Primary Gear Ratio) and O/A Gear Ratio are one in the same. You have no transmission ratio to factor in. We are "assuming" your car is "direct drive".

Rollout ratio takes both the FDR and the tire diameter into account in achieveing a final figure, e.g., "rollout".

Assuming your rail is "direct drive", e.g. spur attaches to RR wheel hub. Pinion engages the spur and is affixed to the motor shaft. That is the RC electric drag racing standard at present. Our rail is an anomoly with belt drive. So we have to factor in a transmission ratio. Works out the same mechanically. We just suffer having additional rotating mass. Rotating mass is the bane of RC drag racing. Lose any rotating mass you can.

Hope this helps.

//AC//



< Message edited by AHR43 -- 7/4/2007 11:08:29 PM >

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RC Electric Drag Racing

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RE: New Dragster - 7/5/2007 2:20:28 AM   
cork44


 

Posts: 62
Joined: 7/30/2006
From: Schererville, IN, USA
Status: offline 		Yes it is direct drive here it is:

[URL=http://imageshack.us] [/URL]


[URL=http://imageshack.us] [/URL]

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       Post #: 8

RE: New Dragster - 7/5/2007 2:46:06 AM   
ProRCRacer88


 

Posts: 1760
Joined: 5/1/2006
From: Richmond, VA, USA
Status: offline 		nice car man!

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RE: New Dragster - 7/5/2007 5:18:36 AM   
cork44


 

Posts: 62
Joined: 7/30/2006
From: Schererville, IN, USA
Status: offline 		Hold on! I made a mistake my gears are 120t spur and 30t pinion. According to the formula provided by nick, my rail should be able to hit 97MPH at 40,000rpm. Thats more like it! Thats what I'm shooting for!! Wish me luck, I'm gonna need it.

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       Post #: 10

RE: New Dragster - 7/5/2007 3:35:59 PM   
griz11


 

Posts: 140
Joined: 8/22/2005
From: Granite Shoals, TX, USA
Status: offline 		I saw one go 94 mph last Sat. Man that is quick. One guy from the club I go to hit 104 at the east coast nats. Watch out if the surface is bumpy. They had big problems in Cali with tires exploding on the electric rigs. Hit a bump get them in the air and whammo big chunks all over the place. I noticed some were running very thin slicks Sat. Less mass so they would tend to stay together if they got off the ground. I'll have some more videos next week from the 4th of July money race at Litespeed. Thats always a good race. Is that a custom built chassis? Doesn't look like anything I've seen before.

Griz

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       Post #: 11

RE: New Dragster - 7/6/2007 12:34:26 AM   
cork44


 

Posts: 62
Joined: 7/30/2006
From: Schererville, IN, USA
Status: offline 		Yes this is a prototype dragster, check it out!

[URL=http://imageshack.us]

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       Post #: 12

RE: New Dragster - 7/6/2007 3:41:42 AM   
ac hauswald


 

Posts: 146
Joined: 3/13/2004
From: Houston, TX, USA
Status: offline 		Trick looking rig. Curious, what's the wheelbase?
//AC//

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RC Electric Drag Racing

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       Post #: 13

RE: New Dragster - 7/6/2007 4:15:42 AM   
cork44


 

Posts: 62
Joined: 7/30/2006
From: Schererville, IN, USA
Status: offline 		Thanks, the Wheelbase is 29 1/4"

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       Post #: 14

RE: New Dragster - 7/9/2007 5:37:46 PM   
Nick2618



Posts: 3656
Joined: 3/15/2007
From: Sarasota, FL, USA
Status: offline 		That dragster looks awsome. Also i am glad that formula i found helped you.

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RE: New Dragster - 7/9/2007 6:20:24 PM   
2916jr


 

Posts: 880
Joined: 1/1/2006
From: Clevland, TN, USA
Status: offline 		that might be a little lighter than walbern cars probably


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       Post #: 16

RE: New Dragster - 7/10/2007 1:57:23 AM   
griz11


 

Posts: 140
Joined: 8/22/2005
From: Granite Shoals, TX, USA
Status: offline 		I've seen the arrow shaft chassis before. Actually I have one. Mine is a dual shaft instead of a single. Looks good but I'd make sure the shaft is pretty stiff especially since its a single piece. Should be a killer.

Griz

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       Post #: 17

RE: New Dragster - 7/10/2007 3:47:38 PM   
2916jr


 

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Joined: 1/1/2006