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Old 09-27-2011, 12:47 PM   #1
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Default How do i find the Rpm's of my motor

I'm trying to do the boost on my Rs and im trying to figure out the the full rmps of my motor

Its a 17.5 d3 the kv is 2300(please dont tell me me rpm is my kv otherwise ill feel stupid)

and i run a 2s 5000 is that matters.
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Old 09-27-2011, 01:41 PM   #2
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Originally Posted by For_the_win View Post
I'm trying to do the boost on my Rs and im trying to figure out the the full rmps of my motor

Its a 17.5 d3 the kv is 2300(please dont tell me me rpm is my kv otherwise ill feel stupid)

and i run a 2s 5000 is that matters.
There is no need to know the exact rpm your motor can spin till, with no load, you will see over 20,000, but for speedo programming purposes, use 11-13,000 as your end rpm, and start around 5k. This only changes when the speedo applies more timing, you can move the range around to find what feels best for your track.
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Old 09-27-2011, 01:46 PM   #3
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Actually, kV is the rating for how many RPM the motor will turn unloaded per volt applied, usually without timing advance.

So, the max unloaded RPM at 1s would be

2300 * 4.2 (full battery) = 9660 RPM
2300 * 3.7 (end race voltage) = 8510 RPM

On 2s:

2300 * 8.4 = 19,320 RPM
2300 * 7.4 = 17,020 RPM

When you add timing on the RS, the motor can turn more RPM than the kV rating would suggest.

On my 17.5 Boosted D3 TC, I usually run around a 6k - 16k RPM range, with a 6.0-6.3 FDR.
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Old 09-27-2011, 05:36 PM   #4
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If you want to know exactly what rpm your car is doing at certain times, you'll need a speed gun, once you know the spped, you can work it out vis the diameter of the tyres and the gear ratio.

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Old 09-28-2011, 11:49 AM   #5
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what is FDR?
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Old 09-28-2011, 11:54 AM   #6
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Final Drive Ratio

FDR = (Spur / Pinion) * Internal Ratio

Example: my T3'11 has 38t diff pulleys with 20t center pulleys, and I use a 114t [64p] Spur with a 36t pinion for running boosted 17.5.

FDR = (114 / 36) * (38 / 20)
FDR = 3.167 * 1.9
FDR = 6.02
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