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  1. #1
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    Advice on motor/esc

    I bought the slash unassembled kit and I wanna fit it with a brushless motor. I'm just getting back into the sport but while I build the kit I'll be making all the steering upgrades and such. I've never understood kv, sensored vs sensorless etc. Can someone point me in the right direction? Thank you!

  2. #2
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    Quote Originally Posted by Michiganmisfit7 View Post
    I bought the slash unassembled kit and I wanna fit it with a brushless motor. I'm just getting back into the sport but while I build the kit I'll be making all the steering upgrades and such. I've never understood kv, sensored vs sensorless etc. Can someone point me in the right direction? Thank you!
    Welcome back! I too just got back to RC a while ago.
    Sensorless brushless is for go fast. Sensored is more for lower speed, high torque applications. Crawlers, rock racers, and such. Basically the esc knows the motor position with sensored so it's easier for the system to deliver max torque instantly. Not needed with higher speed rc's. That's the bare bones explanation lol
    Kv is a number related to the max rpm of the motor. Higher the number, the greater the rpm. But there's a torque curve.
    I recently purchased Castle SW4 brushless system for my LCG slash build. I love it.
    Still dialing in my setup, but it's stupid on 3s lipo.
    Castle Creations has a lot of info on their systems plus nice charts to guide you to the right setup based on your build.
    Of course there are a lot of other brands out there to look as well. I like CC personally.

  3. #3
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    Thank you so much for all the info! I really appreciate it brotha!

  4. #4
    RC Qualifier RCWilly's Avatar
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    For the motor Kv, it determines the rotational speed of the motor at a given voltage. For example, a 3800kv motor running on a 7.4V battery would spin at 28,120 RPM (assuming it has no load), and a 4300kv motor running on an 11.1V battery would spin at 47,730 rpm (also assuming it has no load).

    You may hear that higher kv means higher speed, less torque, and lower kv means lower speed, higher torque. Although it is true in most cases, it isn't always true. Higher kv just means higher RPMs, torque has nothing to do with it. If you want more torque, get a larger motor instead (larger motor = more torque). Also, the reason that most people think that the higher kv higher speed is a general trend is that usually, lower kv means longer motor can, which gives it more torque.

    If I sounded confusing above, just think about it this way: higher kv, higher speed; larger motor, more torque.

    For the sensored brushless motors, they have smoother low-speed startups, since the motor has a sensor-board built in the endcap that determines the rotor position of the motor. Sensorless brushless motors on the other hand cog a whole lot more at low speeds since the ESC does not know the relative position of the rotor. If you drive more at low speeds, a sensored motor is better. If you drive at high speeds or don't mind about smoothness, a sensorless motor is better. Sensorless motors can achieve higher speeds as Scott P said are more affordable and have fewer parts to maintain.

    I also have the Castle SW4 and 3800kv motor (sensorless). I run it on 2s with 16/90 gearing. It has a bunch of power, runs quieter than the brushed motor, and runs very cool. You can also look into the Hobbywing Max10 combo if you want a sensorless combo.

    If you want a sensored setup, look into the Hobbywing XR8 or the Mamba X (Mamba X may be overkill...).

    I know this is a bunch of new info, so feel free to ask any questions you may have. (I know sometimes I can sound confusing)
    Hopefully, this helped!
    Everyday's a gift, thus now is called the present.

  5. #5
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    Thanks guys! Lots of info to take in.

  6. #6
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    So will there be a huge difference between a 3800kv motor and say a 3400kv motor? The 3400kv will just have more torque and less top end speed? Thanks again!

  7. #7
    RC Qualifier RCWilly's Avatar
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    So will there be a huge difference between a 3800kv motor and say a 3400kv motor?
    The 3800kv will be faster by a noticeable amount, but not drastically.

    The 3400kv will just have more torque and less top end speed?
    Not necessarily. If they both have the same size (the motor cans have the same length), then get the 3800kv, since they both will have the same torque. If the 3400kv has a longer motor can, then the 3400kv has more torque.

    The torque of a brushless motor is based more on motor size than kv. Only speed is based on kv.
    Everyday's a gift, thus now is called the present.

  8. #8
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    I use the Hobbywing SC8 esc with a Goolrc 3800kv motor on my 2 wheel drive monster slash. Can run 3s but usually run 2s it's fast enough and more controllable.

  9. #9
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    Quote Originally Posted by RCWilly View Post
    For the sensored brushless motors, they have smoother low-speed startups, since the motor has a sensor-board built in the endcap that determines the rotor position of the motor. Sensorless brushless motors on the other hand cog a whole lot more at low speeds since the ESC does not know the relative position of the rotor. If you drive more at low speeds, a sensored motor is better. If you drive at high speeds or don't mind about smoothness, a sensorless motor is better. Sensorless motors can achieve higher speeds as Scott P said are more affordable and have fewer parts to maintain.
    Not exactly, as a general rule yes, but as technology progresses the RC hobby progresses.

    While sensored systems have a track record of being slower than sensorless systems that is not always true. For example, most new Castle Creations sensored systems actually change to sensorless once you get going fast enough, this way the ESC can power the motor without having to process any positions, obviously allowing for the motor to hit sensorless speeds. Castle also has a load of other cool features that I urge you to check out, I supplied the link below.

    https://home.castlecreations.com/castle-technology

    Sensored systems aren't the only ones that are getting better, sensorless systems have also gotten a fair share of improvements over the years. The VXL-6 ESC on my E-revo 2.0(which is ironically made by Castle) uses feedback from the motor wires to, in a way, sense what position the motor is at in order to smoothly accelerate.

    I think it's pretty neat how far we've come considering just 10 years ago brushless systems were the hot new thing and just becoming popular on RTR cars.
    The present is theirs; the future, is mine.

  10. #10
    RC Champion grizzly03's Avatar
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    Quote Originally Posted by ElectricPropils View Post
    ...The VXL-6 ESC on my E-revo 2.0(which is ironically made by Castle)...
    Since when? The previous ESC the MXL-6s was.

  11. #11
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    Quote Originally Posted by grizzly03 View Post
    Since when? The previous ESC the MXL-6s was.
    I read on a post from a while ago that the VXL-6 ESC was made by Castle and rebranded by Traxxas but I can't seem to find the original post.
    The present is theirs; the future, is mine.

  12. #12
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    I've decided the Castle SV4 3800kv is the way I'm gonna go, unless for some reason something is better. I'm going to use telemetry so that's big on my list. The thought of seeing my speed, rpm, temp voltage etc. Is really appealing to me lol what telemetry setup do you good use if you're into it as well?

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