Help me understand BL motors!

[JennyC6]

Long time nitro nut checking in, finally dipping my toes into the scale/trail scene(Planning on picking up a Kong RC CA-10 kit in the next couple weeks, also playing around with /16th tanks and I have an OG Hornet to modernize), and that means I'm finally getting involved with electric models. I'd have no problem sussing out what kind of glow engine would work in a model, but I've summarily ignored electric for >15 years...when I first came into the hobby glow was the speed king and 'run for 15 minutes charge over four hours' was the rule of the land in electric...so it just never popped into my fleet. Today that's wildly different, with lipos and brushless shifting things pretty much completely the other way 'round.


I do understand how electric motors work and I know a couple things about BL in particular. I know that their kV rating is how fast they'll rotate, no load, on one volt, I know the difference between sensored and sensorless, I know that they'll turn backwards if you get two of the three connections swapped wrong-ways-round. But that sums up what I know of 'em.

I could just poke around with 'Suggest me motors for X vehicle' and get that vehicle running. But I don't want that. I want to learn how to choose a motor for myself, rather than having to rely on everyone else.

So, I turn to you lot. Say I want to get a brushless motor that matches the performance of the 540 brushed can that's in my Hornet right now, but uses significantly less battery to do so, thus granting it much improved runtime and having a more reliable powertrain. What attributes would I look for? And, on the ESC, what attributes do I need to look for besides it being BL capable, having a built-in BEC, and making sure it can support a sensored motor if I choose a sensored motor?

 

[Teng]

https://m.youtube.com/watch?v=yjbc3PMKyGk

https://m.youtube.com/watch?v=BcuhdkCucGA

 

[JennyC6]

Pretty useful vids, and seems to confirm the guesstimate I made using a speed calculator. Looks like I'll be able to make good use of the system I've got in my eBay cart right now.

Thanks a bunch!

 

[Inspector86]

To be honest, for a truck like the Kong RC CA-10 which is not even close to a basher you would be better off with something slow and smooth with lots of torque like a 45T or even a 55T brushed motor and the HobbyWing 1080 ESC.

 

[JennyC6]

Based on what I'm looking to do, I'm thinking I'll get good results out of this setup. In both the CA-10 and my OG Hornet I want something that's energy efficient(We all minmax something and for me that's runtime, literally no such thing as too much runtime for me, and hell I'm planning on running two full size 5000mAh 2s packs in the CA-10 in parallel for 10k mAh total), long-lived(The less I have to wrench on it the better which means high voltage and brushed are both out of the question), and reasonably amusing(I want ~20MPH on flat ground out of both of them, throttle is proportional so I can just not floor it if I'm trying to run a trail). From the maths I've done, that means something close to a 5400kv 540BL for the CA-10. THe setup I linked is close enough. Dunno what kV will work in the Hornet yet, I don't remember its gearing, but if I was to spitball something it'd probably be a 3600-4100kv setup.

planning on 2s batteries in both applications.

 

[Inspector86]

Well, I'm out. Good luck!

 

[allanon1965]

3s would give you much longer run times than 2s and you wouldnt need two very large batteries... but in looking at the video, the brushless you are considering would not be the best choice. That rig will not hold up long doing 20mph ..even on flat ground...its not designed for that speed in my opinion... I would find out what the drive lines and differentials are made of before deciding on brushless and make sure more durable metal upgrades can be used...even 2s brushless will tear up weak parts, more so than a brushed setup

 

[JennyC6]

The only plastic in the driveline is the casing of the transmission. Everything else is metal, the gearing, shafting, full ball bearings right from the start, the works. Tamiya's trucks don't even have ball bearings or metal trans gears and they hold up reasonably well. Interestingly enough, people said the exact same things when I bought my NTC3 and floated the idea of turning it into a rally car. Everyone told me I'd trash it, that it'd break all the time, that it wasn't designed to run in dirt and such, blablabla. 8 years later it runs as well now as it did when it was factory new.


20 isn't even that fast. That's about where an out-of-the-box Tamiya semi truck will cap out if you throw it up in 3rd gear. CA-10's built pretty much from nothing but metal(Aside from the trans case, the only other plastic in it is the bodyshell) so if the Tamiya trucks can handle that speed this one should as well.

It's also worth noting that it won't be constantly running that fast. I just want to be able to do some 'highway' running once in a while. My NTC3 will do an honest 45MPH but I rarely run that faster than 20. This would be capable of 20, but in all likelihood, it'd probably run faster than 10 maybe once in a blue moon. Just because it can go that fast doesn't mean I'll always drive it that fast. Remember, our throttles are proportional. We can simply not floor it all the time.

I'm going 2s because, while I want some speed, I don't want this thing trying to go 30-40+. Volts are speed, current is accel, mAh is runtime, and I'm after runtime more than anything else. So i'm going with 2s. 3s would work, sure, but I have no need for an 11 volt system. 7.4 is more than enough. And I'd still run two packs anyway, because again, my main priority is runtime. I can reach the speeds I want on 2 cell batteries. I also don't want to spend a small fortune on batteries and as it is I'm looking at 60 bucks for the two 2s 5000mAh packs I'm planning on getting. 3s 5000mAh packs will inflate that price far more than I can manage. I will grant I've got high quality packs in my eBay cart, and I could cheap out, but I'd rather buy quality over quantity. Especially with lithum batteries.

 

[mewalsh100]

Volt up, Gear down. 3s will offer a lot more efficiency and you can gear down to achieve the target speed you want (20mph). Check out the threads by John Holmes of Holmes Hobbies. The guy has forgotten more about Brushless and Brushed motor systems, ESC's, etc than 99.99999% of people ever knew!

 

[JennyC6]

I'll think about it but there isn't much wiggle room regarding gearing with this thing. It's pretty much fixed. There's some minor fine tuning one can do, but from what I can tell you're pretty much only playing with a difference of 3 or 4 teeth on the pinion as your total adjustment range, and that's not enough to compensate for another 4 volts or so.

 

[allanon1965]

The only plastic in the driveline is the casing of the transmission. Everything else is metal, the gearing, shafting, full ball bearings right from the start, the works. Tamiya's trucks don't even have ball bearings or metal trans gears and they hold up reasonably well. Interestingly enough, people said the exact same things when I bought my NTC3 and floated the idea of turning it into a rally car. Everyone told me I'd trash it, that it'd break all the time, that it wasn't designed to run in dirt and such, blablabla. 8 years later it runs as well now as it did when it was factory new.


20 isn't even that fast. That's about where an out-of-the-box Tamiya semi truck will cap out if you throw it up in 3rd gear. CA-10's built pretty much from nothing but metal(Aside from the trans case, the only other plastic in it is the bodyshell) so if the Tamiya trucks can handle that speed this one should as well.

It's also worth noting that it won't be constantly running that fast. I just want to be able to do some 'highway' running once in a while. My NTC3 will do an honest 45MPH but I rarely run that faster than 20. This would be capable of 20, but in all likelihood, it'd probably run faster than 10 maybe once in a blue moon. Just because it can go that fast doesn't mean I'll always drive it that fast. Remember, our throttles are proportional. We can simply not floor it all the time.

I'm going 2s because, while I want some speed, I don't want this thing trying to go 30-40+. Volts are speed, current is accel, mAh is runtime, and I'm after runtime more than anything else. So i'm going with 2s. 3s would work, sure, but I have no need for an 11 volt system. 7.4 is more than enough. And I'd still run two packs anyway, because again, my main priority is runtime. I can reach the speeds I want on 2 cell batteries. I also don't want to spend a small fortune on batteries and as it is I'm looking at 60 bucks for the two 2s 5000mAh packs I'm planning on getting. 3s 5000mAh packs will inflate that price far more than I can manage. I will grant I've got high quality packs in my eBay cart, and I could cheap out, but I'd rather buy quality over quantity. Especially with lithum batteries.

fine, but you are way off on the price of 3s...I can get 2 3s 5000mah lipos for 56 bucks...and they will last far longer than 2 2s 5000mah batteries...mah is not the true gauge of run time.. efficiency is the gauge. As you stated, you can control the speed by your throttle input so the 3s should be no different than 2s if you control the speed. The potential will be there for more with 3s but you dont have to pull full throttle...I have been using the lipos from value hobby for many years and they have outlasted the turnigy and smc and venom batteries I have ran in the past, as well as being very affordable..."thumbsup"

 

[allanon1965]

I'll think about it but there isn't much wiggle room regarding gearing with this thing. It's pretty much fixed. There's some minor fine tuning one can do, but from what I can tell you're pretty much only playing with a difference of 3 or 4 teeth on the pinion as your total adjustment range, and that's not enough to compensate for another 4 volts or so.

this is also incorrect...4 teeth can make a big difference with a lipo and electric motors

 

[mewalsh100]

this is also incorrect...4 teeth can make a big difference with a lipo and electric motors

Absolutely! 4 teeth is a rather huge jump. Consider i'm running 56T spur, 10T pinion. (As I do). Then I jump up to a 14T pinion. - That would yield a huge increase in top speed, but put way too much load and stress on the motor and esc. 5.6:1 versus 4.0:1 - That is a LOT!

 

[Duuuuuuuude]

Your going to regret a 5700kv in the CA10, especially with limited gearing options.


You don't necessarily need to gear down/volt up, you can also kv down/volt up.

 

[Ninomaniac]

^ What he said! 3500-ish KV on 3s makes a lot more sense.