V8-muscle

Hi I am new to the rc world and have some questions that haven't been answered.
- why is the KV # to turns number differ from 1/18 scale to 1/10 scale?
Ie. I recently bought a 17.5T 1/10th scale motor matched to a 60 amp fan cooled esc. This thing is so slow!
After further investigation I see it's a 1900KV motor. If this was a 1/18 scale I would expect 4000KV.

SyCo_VeNoM

better yet it varies brand to brand even for the same size motors

I ignore the turns completely and go strictly by Kv ratings

iexion

most if not all 1/18 sized motors or "380" sized motor ive seen usually have a higher KV rating then a 540 sized (1/10) motors. Thats not to say you cant find a high kv 1/10 motor.
Ball park range:
1/18 motor = 7000kv
1/10 motor = 4000kv
1/8 motor = 1950kv

This IS NOT exact but its to give you a good idea where the size of motor is based on scale of the vehicle.

1/18 scale motor can "rev" higher then a 1/10 per say. As you get into "bigger sized" motors you dont have the high kv but start to see more bottom end raw torque. keep in mind when you start talking 1/8 motors you start looking to require more power (like a 1/8 scale Brushless Monster truck running on two 3s batteries)

Pay attention to the turn of the motor if you intend to race. My 1/10 touring car is spec (26mm tires, 17.5t motor etc)

Brand of motor does vary the kv rating. If you want more speed find a higher kv motor and.... a good battery. I dont want to get on to the subject of batteries because this is on a subject of motors

Welcome to RCU btw

Foxy

Moved from off topic to general discussion...

Welcome to RCU

The KV aren't different per se, just different numbers are optimal for different scales. Kv is just a unit that says how many rpm a motor will spin for each volt supplied, it applies equally whatever the scale or size of the motor. We generally want faster as hobbyists, because fast is fun in most cases, so theoretically we should go for higher kv whenever possible. The trouble is that as you increase kv you increase startup load, so the heavier the vehicle, the lower the kv needs to be to keep current levels manageable. That's why you'll generally see the approximate numbers that Iexion described. For what it's worth, 1/5th motors will generally be in the 500 to 1000kv range.

V8-muscle

Thanks everyone, helpful words. Hey I have another thread out there for helping me set up or buy new. Search me out, appreciate the help

V8-muscle

Iexion, your 1/10th ride with a 17.5t, what's your top speed on it? I feel I'm only getting maybe 15mph

Foxy

17.5s are slow motors, but because of the low kv, can be geared a bit higher before heat becomes a problem. Usually, a 17.5 motor is reserved for what is called the 'stock' racing class, but also in many cases a 17.5 motor will accept quite aggressive timing adjustments (if you aren't sure what timing is, don't play with it, it can make the motor very fast, but also very hot, and requires an expensive ESC to be done properly). Are you racing in the stock classes? If not, then I suggest picking up a motor in the 9 to 10.5 turn range (3800-4500kv) to give you a good balance of speed and heat with appropriate gearing. 10t (4000kv) seems to be the sweet spot for 1/10th RWD, it can accept a wide range of gearing without too many issues.

iexion

I hit 26mph via GPS but its a little over geared @ 35/69. I should back it down to something like 30/72.
As far as the ESC timing as Foxy mention, if your Local Hobby Store (lhs) is racing based off R.O.A.R. specs you'll need to get all the specs before you decide to get a different motor and or esc. my Novak Havoc has adjustable timing but I Never mess with it being 1. My local races require "Locked timing" 2. Its a great way to fry something unless you really know what your messing with.

V8-muscle

Thanks guys

V8-muscle

So I tried a 28/75T set up, I was pretty happy.  Lot of torque still and a better top end.

iexion

Thats about what im going to try. 30/72 if i can find my gears
[:@]

ryan_t888

Here's a general chart for [link=http://www.radiocontrolinfo.com/ElectricCar/motor.php]Voltage and motor KV[/link].