RC-Monster Forums - View Single Post - Noobie to Brushless, need little help/advice!

BrianG · 03.01.2007, 09:02 PM

I see a couple of problems there.
- Your voltage is too low at 7.2v. You should enter 14.4 for 2x6cells packs, or 16.8 for 2x7cell packs. Because the voltage is so low, the motor kv has to be extremely high to compensate.
- You want a 15lb truck to go 50mph! Wow. While possible, you're gonna need some serious power.
- It looks like you chose 1st gear as the tranny ratio. You're gonna be hard-pressed to get 50mph in first gear. Imagine what 2nd gear would do!

Most people lock their trannys in second gear - BL has so much power that first gear is useless unless you want to go very slow a lot.

I entered some more reasonable values and came up with this:

Vehicle Weight (approx): 15
Desired top speed in MPH: 45
Differential Ratio: 2.8461538461538462
Transmission Ratio: 1.7222222222222223
Additional Ratio: 1
Spur Tooth Count: 64
Pinion Tooth Count: 22
Battery Voltage: 16.8
Tire Diameter (inches): 5.75
Total Ratio: 14.25952 : 1
Tire Circumference: 18.064 inches (458.83 mm)
Required Motor RPM: 37511.425 RPM
Required Motor KV: 2232.823 RPM/V
Good Motor Choices: BK Wanderer 7 XL (kv=2145)
Better Motor Choices: No motors of this class fit the parameters you entered.
Best Motor Choices: Neu 1515 1y (kv=2200) LMT 1940/7 (kv=2239) LMT 1950/6 (kv=2178)

	(#7)
BrianG RC-Monster Admin Offline Posts: 14,609 Join Date: Nov 2005 Location: Des Moines, IA	03.01.2007, 09:02 PM I see a couple of problems there. - Your voltage is too low at 7.2v. You should enter 14.4 for 2x6cells packs, or 16.8 for 2x7cell packs. Because the voltage is so low, the motor kv has to be extremely high to compensate. - You want a 15lb truck to go 50mph! Wow. While possible, you're gonna need some serious power. - It looks like you chose 1st gear as the tranny ratio. You're gonna be hard-pressed to get 50mph in first gear. Imagine what 2nd gear would do! Most people lock their trannys in second gear - BL has so much power that first gear is useless unless you want to go very slow a lot. I entered some more reasonable values and came up with this: Vehicle Weight (approx): 15 Desired top speed in MPH: 45 Differential Ratio: 2.8461538461538462 Transmission Ratio: 1.7222222222222223 Additional Ratio: 1 Spur Tooth Count: 64 Pinion Tooth Count: 22 Battery Voltage: 16.8 Tire Diameter (inches): 5.75 Total Ratio: 14.25952 : 1 Tire Circumference: 18.064 inches (458.83 mm) Required Motor RPM: 37511.425 RPM Required Motor KV: 2232.823 RPM/V Good Motor Choices: BK Wanderer 7 XL (kv=2145) Better Motor Choices: No motors of this class fit the parameters you entered. Best Motor Choices: Neu 1515 1y (kv=2200) LMT 1940/7 (kv=2239) LMT 1950/6 (kv=2178)