Hobbywing 3660 with 3150kv or 3700kv ? Monster slash 2wd.

[cocoune]

Hi, its a really specific question.
I'm thinking about this for weeks now.
I want to change my esc motor combo on my monster slash bl2s 2wd and i want either a spektrum firma (at my lhs) or the hobbywing quickrun and 3660 motor its all the same price. But the kv confuse me.

For spketrum i would get what my lhs gives me but with the hobbywing i have the choice between 3150kv and 3700kv.

I like heavy offroad. I jacked my suspension for that. I heard higher kv is "better" because i can gear down if needed and have less cogging that way than bigger pinion and lower kv.

 

[DavidB1126]

For spketrum i would get what my lhs gives me but with the hobbywing i have the choice between 3150kv and 3700kv.

I like heavy offroad. I jacked my suspension for that. I heard higher kv is "better" because i can gear down if needed and have less cogging that way than bigger pinion and lower kv.

True, I think. (If experts can clarify that)

And it also depends on what battery you are running.

2s, id go 3700kv
3s, id go 3150.
If you do both you can always get the lower kv motor and gear up too.

I run a ezrun 4000kv (discontinued) in mine with tall tires, and stock vxl spec gearing, on 2s, rarely does it overheat and it is a beast of a set up.

 

[cocoune]

True, I think. (If experts can clarify that)

And it also depends on what battery you are running.

2s, id go 3700kv
3s, id go 3150.
If you do both you can always get the lower kv motor and gear up too.

I run a ezrun 4000kv (discontinued) in mine with tall tires, and stock vxl spec gearing, on 2s, rarely does it overheat and it is a beast of a set up.

Well i forgot to mentioned i plan to go 3s. If i get a 3700kv i can gear down ? Idk why ppl say 3150 for 3s. They are both 3s rated on hobbywing site. Thats what i dont get with kv.

 

[DavidB1126]

Theoretically you could run 3s on 3700 and be fine. But imo it's too much power.

Kv is confusing lol

 

[332_RC]

3s up to like 4100kv for On road. Off road, it would overheat. 3200kv - 3s off road is good. Spektrum makes a 3660 3200kv 3s motor. $39 on jennys.com.

 

[cocoune]

3s up to like 4100kv for On road. Off road, it would overheat. 3200kv - 3s off road is good. Spektrum makes a 3660 3200kv 3s motor. $39 on jennys.com.

And what if i just gear down to stop the overheat ?

And yea i can't decide between hobbywing and spektrum. Where i live they are all the same price. Maybe a bit cheaper on jennyrc but idk with the fees.

 

[332_RC]

And what if i just gear down to stop the overheat ?

And yea i can't decide between hobbywing and spektrum. Where i live they are all the same price. Maybe a bit cheaper on jennyrc but idk with the fees.

Probably 2wd 3700kv on 3s would be fine. Probably gear down. What's the current pinion?

 

[cocoune]

Probably 2wd 3700kv on 3s would be fine. Probably gear down. What's the current pinion?

Right now I'm 18/83 with 2.8 tires. Stock is 21/83.

 

[332_RC]

Right now I'm 18/83 with 2.8 tires. Stock is 21/83.

I have a 3500kv in a 2wd RC, Gorgon, on 2s. A little lethargic, but lotsa power to the tires. I wish Ida gone 3900kv 2s, or I need to run 3s in it, as is. I kept the stock gears, & went up in tire size, so it's a little sluggish off the go, but gets decent speed.

 

[Beer_Goggles_RC]

Higher KV is going to produce more power at the expense of higher amp draw and heat. If you over KV a rig you will get more power (given your esc and battery can deliver that power) but your motor and esc run the risk of overheating.

3700 on 3s with the correct gearing is just fine. If you can add a cooling fan to the motor and esc then that’s always a plus.

I always use a gearing calculator when I’m not sure where to start with my gearing. The So Dialed gear ratio calculator always lands me on a great ratio. From there you can gear up or down depending on how much heat your motor and esc are producing. Once you hit 190 then it’s likely time to gear down.

If you do a lot of running on grass then just go lower KV. Grass is really demanding on electronics.

 

[Cheetah928]

Hi, its a really specific question.
I'm thinking about this for weeks now.
I want to change my esc motor combo on my monster slash bl2s 2wd and i want either a spektrum firma (at my lhs) or the hobbywing quickrun and 3660 motor its all the same price. But the kv confuse me.

For spketrum i would get what my lhs gives me but with the hobbywing i have the choice between 3150kv and 3700kv.

I like heavy offroad. I jacked my suspension for that. I heard higher kv is "better" because i can gear down if needed and have less cogging that way than bigger pinion and lower kv.

Yes, denfinently. I’ve run the 3300 kv bl-2s, and the 3500kv vxl, the vxl out performs it really depends on what you wanna do. KV basically translates to rpm, which you want to hear your slash down. I personally run a slash, but I’m more street style. I know just about everything to know on that car, so let me know with further questions. Honestly, the VXL system is great, but not for heavy heavy off road. I run it in a dirt trail that’s pretty easy and that’s about it. Maybe it’s because I’m in suburban area of Colorado?

 

[RustyUs]

There are RC gearing/speed calculators out there for use. I see @Beer_Goggles_RC has mentioned it already. Great for situations like this. Plug in numbers for Kv, battery voltage, tire size, gear ratio... voila! Can help make decision easier on what Kv to buy. Plug in numbers of current setup vs. what you think you might buy/install.

As far back as I can remember 1/8 scale buggy owners have said 1900kv motor and 16T pinion as the default answer. Me... I use a 1700kv motor simply, because I get better use out of the powerband on a shorter/tighter track.

Is a 3660 size motor needed for your 2wd RC? Is your drivetrain up for the task? I'm just trying to get you to think of all the angles when upgrading/replacing things.

Your driving style/environment may dictate something else more useful.

 

[cocoune]

3700 on 3s with the correct gearing is just fine. If you can add a cooling fan to the motor and esc then that’s always a plus.

Well both 3150kv and 3700kv seems goodbfor 3s thats why i find it hard to choose. Especially with gearing that i can change. I do heavy heavy offroad and grass (a little). I have 2.8 tires, bigger suspensions and longer a arms. Lower kv seems better from what i see. Not completely sure why tho. I'm afraid to make an "annoying mistake" lol I dont do street at all.

Is a 3660 size motor needed for your 2wd RC? Is your drivetrain up for the task? I'm just trying to get you to think of all the angles when upgrading/replacing things.

Your driving style/environment may dictate something else more useful.

I want to try 3s speed. The spketrum come with a 3660 can and the hobbywing is 3652 or 3660. I heard alot of good thing with the 3660 and many tried it without issues so i guess ill be fine !

 

[Beer_Goggles_RC]

Since it’s a bl2s slash I believe you won’t be able to run a motor fan. 3150 and 3700 really aren’t that far apart but I’d personally go with the 3150 for bashing, really a 3s 3700 is gonna be an excessive amount of power for a 2wd sct (or even 3s in general ) you’ll have a hard time keeping it straight when it’s not doing constant wheelies if you do plan on going back to 2s the 3150 will be slightly slower than the stock bl2s motor and the 3700 will be a hair faster

From what I’ve read the bl2s is 3300kv which is what Traxxas felt was a good balance between speed and reliability for 2s

 

[TeknoJ]

My vote is for a 3S system with the 3150/3200kv - ish.

Then gear accordingly

 

[cocoune]

My vote is for a 3S system with the 3150/3200kv - ish.

Then gear accordingly

Yea the 3150kv looks like the right answer even if i dont really know the wcience behind it. I dont understand the difference between higher kv/lower gearing and lower kv/higher gearing

Since it’s a bl2s slash I believe you won’t be able to run a motor fan. 3150 and 3700 really aren’t that far apart but I’d personally go with the 3150 for bashing, really a 3s 3700 is gonna be an excessive amount of power for a 2wd sct (or even 3s in general ) you’ll have a hard time keeping it straight when it’s not doing constant wheelies if you do plan on going back to 2s the 3150 will be slightly slower than the stock bl2s motor and the 3700 will be a hair faster

From what I’ve read the bl2s is 3300kv which is what Traxxas felt was a good balance between speed and reliability for 2s

Like i already said do you no why i can't just lower the gearing with higher kv ? Anyway i think ill go with 3150 anyway since almost everybody tell me it would be better for what i do. Btw with the modif i did the car is (i think) extremely stable. The handling is nowhere near of when it was stock.

Are you sure i can't put a fan on the motor ? I will check but i think its possible.

 

[CertifiedMike]

I don't own a Slash. My comments are based on repowering other brands.
The biggest issue I could see in a large motor/high kv is that the car may simply not be up to taking that power all the time.
I feel like the Arrma Granite 3s is an excellent example of this.
Its not the stability, its the shafts breaking and I ripped a wheel center out. The steering doesn't work great with the speed of 3s... I don't know if the Slash is actually good for 3s abuse long term.
A "too big"motor with a tiny pinion will work but its sopping up a lot of power to avoid a little cogging imo.
A smaller pinion will get you lower speeds as well.
I bought a 3800kv 3652 Spektrum from Jennys for under $30. You could always go that route (buy a cheap motor I mean) and then you'll have some basis for what system you actually need. (not sure if Slash stock is 3652 or 3660 but stay with that size imo)
I found myself sort of lost with brushless too. New terms that seemed to almost conflict with what I thought I knew about brushed systems.
In my case, I blew a motor (it was actually a broken wire) so I just said screw it and jumped in.
Its not really all that confusing really. You'll pick it right up I'm sure.
Even if you buy a 3100, 32, 33...kv motor and want something faster, the 3300 motor isn't a 'dud'. You can always put it in another r/c later or sell it to finance the next motor.

 

[TeknoJ]

Yea the 3150kv looks like the right answer even if i dont really know the wcience behind it. I dont understand the difference between higher kv/lower gearing and lower kv/higher gearing


Like i already said do you no why i can't just lower the gearing with higher kv ? Anyway i think ill go with 3150 anyway since almost everybody tell me it would be better for what i do. Btw with the modif i did the car is (i think) extremely stable. The handling is nowhere near of when it was stock.

Are you sure i can't put a fan on the motor ? I will check but i think its possible.

Did somebody say SCIENCE????!
You cannot simply gear down a high KV motor and expect it to be ok, here is what I DO know:
1) All motors have a rated RPM threshold that you cannot exceed because it will damage the internal components of the motor. Lets say a motor is rated for 50,000 RPMs. A fully charged battery cell is 4.2-4.25 volts. Multiply that by your battery's cell count (2s or 3s). For example: Lets take a 3s battery voltage (fully charged), which would be roughly 12.75 volts, and multiply that by the motor's KV which is 3150, and that should equal 40,162.5 RPMs. If that motor is rated to withstand 50-60,000 RPMs then we are good. Factoring in gearing ratios n all that well, I'm not certain how that can change the RPMs the motor will see but it should be safe to gear accordingly based on heat of the motor after you do a few hi-speed passes. This is why we say monitor your temps of the ESC and motor.
2) Lets over volt that same motor with 4s. A fully charged 4s battery can be around 17 volts. Multiply 17 by 3150 and we come up with about 53,550 which is just over our RPM threshold. The voltage alone will smoke that motor like a phat blunt my guy. Factor in some gearing and it could be worse. You can not just over volt or over rev a motor and expect it to be reigned in by gearing alone because it will most likely run very hot, too hot.
Does all that make sense?

 

[TeknoJ]

In addition: If we go up in volts we gear down, like from a 20 tooth pinion to an 18,17, or 16. If we volt down we could gear up from a 16 tooth pinion to a 17, 18, or 19, in increments of one or two teeth at a time while monitoring temps.

 

[cocoune]

I don't own a Slash. My comments are based on repowering other brands.
The biggest issue I could see in a large motor/high kv is that the car may simply not be up to taking that power all the time.
I feel like the Arrma Granite 3s is an excellent example of this.
Its not the stability, its the shafts breaking and I ripped a wheel center out. The steering doesn't work great with the speed of 3s... I don't know if the Slash is actually good for 3s abuse long term.
A "too big"motor with a tiny pinion will work but its sopping up a lot of power to avoid a little cogging imo.
A smaller pinion will get you lower speeds as well.
I bought a 3800kv 3652 Spektrum from Jennys for under $30. You could always go that route (buy a cheap motor I mean) and then you'll have some basis for what system you actually need. (not sure if Slash stock is 3652 or 3660 but stay with that size imo)
I found myself sort of lost with brushless too. New terms that seemed to almost conflict with what I thought I knew about brushed systems.
In my case, I blew a motor (it was actually a broken wire) so I just said screw it and jumped in.
Its not really all that confusing really. You'll pick it right up I'm sure.
Even if you buy a 3100, 32, 33...kv motor and want something faster, the 3300 motor isn't a 'dud'. You can always put it in another r/c later or sell it to finance the next motor.

I heard that it would be alot of fun to try 3s on a 2wd and i think its nice to feel the power even if i dont go full throttle and ill have more torque with the 3660. But I'm still not sure between spektrum and hobbywing.

In the summer i need to gear down so it will help a little in the summer.

Did somebody say SCIENCE????!
You cannot simply gear down a high KV motor and expect it to be ok, here is what I DO know:
1) All motors have a rated RPM threshold that you cannot exceed because it will damage the internal components of the motor. Lets say a motor is rated for 50,000 RPMs. A fully charged battery cell is 4.2-4.25 volts. Multiply that by your battery's cell count (2s or 3s). For example: Lets take a 3s battery voltage (fully charged), which would be roughly 12.75 volts, and multiply that by the motor's KV which is 3150, and that should equal 40,162.5 RPMs. If that motor is rated to withstand 50-60,000 RPMs then we are good. Factoring in gearing ratios n all that well, I'm not certain how that can change the RPMs the motor will see but it should be safe to gear accordingly based on heat of the motor after you do a few hi-speed passes. This is why we say monitor your temps of the ESC and motor.
2) Lets over volt that same motor with 4s. A fully charged 4s battery can be around 17 volts. Multiply 17 by 3150 and we come up with about 53,550 which is just over our RPM threshold. The voltage alone will smoke that motor like a phat blunt my guy. Factor in some gearing and it could be worse. You can not just over volt or over rev a motor and expect it to be reigned in by gearing alone because it will most likely run very hot, too hot.
Does all that make sense?

Thanks ! I got what you said but 3150kv and 3700kv are both rated for 3s thats why I'm lost.