1/8th KV - Why change? - RCCanada - Canada Radio Controlled Hobby Forum
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Old 03-18-2011, 10:38 AM   #1
MikeZ
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1/8th KV - Why change?


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Hey all! I am new to 1/8th Electric and would like to know a little more about KV rating and what is a good choice.

I was told that at the Can Champs coming up most people use 1700-2050kv rating.

My question would be why would I get one over the other? I do understand what KV rating does however does it also effect torque?

With the 'turbo' functionality why wouldn't I just go with a lower KV(more torque?) and then boost for more top speed depending on track?

I will be making a purchase soon so I just want to buy the best that will fit my needs.
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Old 03-18-2011, 11:03 AM   #2
tekno
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lower kv more torque less speed, higher kv the more top end less torque. Also they are short and long can motors. The long can motors are for truggy and produce more torque than the shorter cans. The short can motors are more for buggy. The higher KV motors need good lipos as well at least 35C and up imo.

Added: I see allot of people with 1700kv or 1900kv when you have a higher kv (ex 2050) motor the power could become too much to handle especially when you race the 1700 or 1900 has a good balance of torque and speed and you can control the car better because, there not too much power but just enough and also i think there more efficient.

bottom line

higher kv= wants speed and to bash
lower kv= more control and wants to race

This is my opinion.
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Old 03-18-2011, 11:06 AM   #3
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Hi MikeZ,

My first post was today and I don't _really_ know what I'm talking about... but I've been doing a lot of Googling about the same thing (as I need electronics for my 1/8th buggy as well). So somebody please correct me if I have this wrong:

I believe brushless motors are more efficient running high volts at lower amps (where high amps through the same wires = heat = wasted battery power). So even if a 4000kv (kv = 1000 RPM per volt) motor on a 2s battery spins at the same speed as a 2000kv motor on a 4s battery... that 2000kv setup would get a longer runtime as it wastes less battery power on heat.

If you wonder why people don't just run a 4000kv motor on 4s (or higher) battery to get crazy speeds, I think it's because racers are also targetting specific motor RPMs that are efficient and controllable (i.e. uncontrolled wheelspin doesn't help them) - I've seen numbers quoted like 30000-32000 RPM. So, how do you run high "s" battery packs (4+) and still hit that RPM range? You run a lower kv motor. (i.e. 4s = 14.8volts x 2000kv motor = 29600 RPM ...or... 6s = 22.2volts x 1400kv motor = 31080 RPM).

I think one of the downsides of the high "s" batteries is that they tend to be larger and heavier... so you see people run 4s-6s more on 1/8th scale cars because weight and space to mount them are less of an issue. Also, high volt batteries may require more expensive ESC etc...

- Mike
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Old 03-18-2011, 11:12 AM   #4
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Thanks for the posts.


I am familiar with KV values and thank you for confirming that the lower KV is higher torque.

I think I will get a 1900kv Tekin for my 1/8th and see how it goes.
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Old 03-18-2011, 11:59 AM   #5
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1900 or 2050 are great choices but the track I raced on needs a 2050 for the straights,thats the only place I needed it though,nice to have it and just gear down a bit as well.tekin software and gearing will let you tune very well too.I had both so on shorter technical tracks I could swap em out,only a hundred bucks for a motor and nice to have a spare just in case lol.most people should be concerned with esc temps as well they are a good sign of tuning etc...ps my motor never hit over 175 in the hottest days and I was not getting pulled by anyone on the straights.I loved the power and it was geared up a bit stupid
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Old 03-18-2011, 12:02 PM   #6
bobf24
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Quote:
Originally Posted by Aronek View Post
Hi MikeZ,

My first post was today and I don't _really_ know what I'm talking about... but I've been doing a lot of Googling about the same thing (as I need electronics for my 1/8th buggy as well). So somebody please correct me if I have this wrong:

I believe brushless motors are more efficient running high volts at lower amps (where high amps through the same wires = heat = wasted battery power). So even if a 4000kv (kv = 1000 RPM per volt) motor on a 2s battery spins at the same speed as a 2000kv motor on a 4s battery... that 2000kv setup would get a longer runtime as it wastes less battery power on heat.

If you wonder why people don't just run a 4000kv motor on 4s (or higher) battery to get crazy speeds, I think it's because racers are also targetting specific motor RPMs that are efficient and controllable (i.e. uncontrolled wheelspin doesn't help them) - I've seen numbers quoted like 30000-32000 RPM. So, how do you run high "s" battery packs (4+) and still hit that RPM range? You run a lower kv motor. (i.e. 4s = 14.8volts x 2000kv motor = 29600 RPM ...or... 6s = 22.2volts x 1400kv motor = 31080 RPM).

I think one of the downsides of the high "s" batteries is that they tend to be larger and heavier... so you see people run 4s-6s more on 1/8th scale cars because weight and space to mount them are less of an issue. Also, high volt batteries may require more expensive ESC etc...

- Mike
this is pretty much a bang on description IMO, when I was buying my stuff I was looking at what batteries I wanted to run, and then picked a KV motor that put me in the RPM range I wanted, you will be happy with 1900kv though, if you run indoor 3s or 4s will be perfect and for a big outdoor track 4s or 5s if you want some extra spank,
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Old 03-18-2011, 12:21 PM   #7
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I run the Tekin 2050kv on 4s in my 1/8 ebuggy. I think it's a great motor. Good combination of speed and torque. I would not go any bigger personally. I have driven my friends buggy ( we have the same buggy) he has the Tekin 1900kv on 4s. Again, it's a great set up. You'd be happy with either.

What buggy are you looking at getting?
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Old 03-18-2011, 12:43 PM   #8
BigR
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Quote:
Originally Posted by MikeZ View Post
With the 'turbo' functionality why wouldn't I just go with a lower KV(more torque?) and then boost for more top speed depending on track?
Boost typically doesn't work very well with 1/8 systems, yielding only about 10% more power to the motor at a great efficiency cost.

It's not quite the fine balance between torque and power that you find in 1/10 motors. 1/8 4-pole setups produce a large enough amount of torque, across all the kV ratings (but remember, no short cans in truggies), it's more a balance between power, drivability, and efficiency.
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Old 03-18-2011, 05:01 PM   #9
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and you can only run boost when in fully sensored mode too on tekin
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Old 03-18-2011, 05:25 PM   #10
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Go Nitro,, so much more fun..
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