What could be wrong with my setup?

[Bmr4life]

Trying to figure out why my Jammin CRT .5 is not hitting the top speed it should be according to the online calculator.

Stock 46t spur and stock diffs. 25T pinion. Castle 2650kv motor on 2s and 3s. 4.5" buggy tires.

Calculator says it should go ~44mph on 2s and ~66mph on 3s.

My actual speeds are 28mph and 43mph.

The motors is less than 120F on both packs.

What am I doing wrong?

[Arct1k]

Tire diam?

[Bmr4life]

Yeah, I got that correct too. Whats really confusing is the speed are off at the same degree.

The calculator says I should be getting 22mph per 3.7 volts of lipo power.

GPS says I'm getting ~14mph per 3.7 volts.

[Bmr4life]

Also, on 3s it can pop wheelies from a stand still easily. I don't think its over geared given this and the low temps. Lastly, the batteries should be good for 125amps.

[_paralyzed_]

the motor isn't spinning 2650rpm/v then... do a kv check

[Bmr4life]

Originally Posted by _paralyzed_

the motor isn't spinning 2650rpm/v then... do a kv check

How do I do that?

Would this work?

Method 3 (Colin Dedman's formula)

1. Drive the motor with a drill press.

2. Measure RPM and voltage generated (by one phase).

3. Kv = RPM / (volts x 1.41 x 0.95)

[_paralyzed_]

your speeds match up to 1650kv. weird.

[Bmr4life]

So how do I get the kv of a brushless motor?


Update.

Just ordered a RPM-KV meter. Looks like a cool little device.

[Overdriven]

If you have a castle esc and castle link for pc you can do the kv check, it's part of the procedure for setting up Torque Control.

[Bmr4life]

Originally Posted by Overdriven

If you have a castle esc and castle link for pc you can do the kv check, it's part of the procedure for setting up Torque Control.

Really? Cool. I'll look into that tomorrow. Thanks

[zeropointbug]

What diff ratio does it have?

[Bmr4life]

3.25 according to the calculator and google.

[BrianG]

What are you using for battery voltage on the calc? 3.7v per cell should be the one to use.

[Bmr4life]

3.7v

Also, its not my first time using the calculator. I've been able to match up my Savage Flux pretty good, its within 3mph.

[BrianG]

Try exporting everything and pasting it here. Maybe there's just something being overlooked...