Clarifying The Most Common Myth In RC: Importance Of Motor KV Explained

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@mjetdevelopment 3 ай бұрын

Join the official M-Jet Facebook group! facebook.com/groups/623045356071128 Supersprint files available for purchase: www.cgtrader.com/3d-print-models/hobby-diy/other/m-jet-sprint-3d-printable-rc-jetsprint-boat-model Supersprint hardware kit by RCPrinter: rcprinter.com/products/m-jet-supersprint-v1-0-build-kits

@lutach 6 ай бұрын

Something that I was doing over 14yrs ago (I think rofl) when not many understood the value of HV. Glad to see that the HV topic is alive and well.

@kekse1669 6 ай бұрын

Today I was finally able to test my new Supersprint. Holy shit is it a huge difference compared to the Sprint. Thank you very much that it is a "free" upgrade if you have already bought the old boot. You are a huge asset to the modeling community keep up the good work.

@mjetdevelopment 6 ай бұрын

Amazing, glad to hear!

@sharpnesstherapy502 6 ай бұрын

Jettle

@thedarron420 6 ай бұрын

Dude is smart, finally made sense of this to me. Thanks Bro!

@BloodyMobile 6 ай бұрын

8:40 I was already wondering what all that 2S ... 6S stuff meant. I knew it was related to the battery but that chart made it instantly obvious. Really a great explaination on these things. Especially why it's better to use 6S vs 2S (and what as a result also to keep in mind) 👍

@robbierobison 7 ай бұрын

Great video! So essentially running a larger and larger motor allows for more power generation. Does that mean that the boat would be fastest on a 40xx motor? If so, what KV motor would you recommend for 6s?

@mjetdevelopment 7 ай бұрын

Thanks. I haven't measured a 40xx motor, but I assume that for example a 4074 1800kv motor would achieve more RPM than the 3660 1800kv, staying more efficient even though the same RPM is demanded from it, making 1600-1800kv a viable choice. However a 40xx motor is too big for the Supersprint.

@robbierobison 7 ай бұрын

@@mjetdevelopment Makes sense! Thank you!

@geekmidget 3 ай бұрын

@@mjetdevelopment In relation to the doubt by @robbierobison: suppose one uses a 4074 motor in a longer boat (lets say 600-700mm), but aiming for 4S to reduce costs on batteries. Do you think a 120A ESC could be enough (assuming the 30mm supersprint drive is capable of pulling a boat that long)? Also, if I may ask: 31080rpm unloaded should be close to 23000-25000rpm with load. Is there a particular reason why you aim for that number instead of something more conservative for components like 18000-20000rpm loaded?

@mjetdevelopment 3 ай бұрын

@@geekmidget To the first question - which KV on the 4074 are you aiming for? If I know that I can estimate the amp draw for you, when using the Supersprint pump. The loaded RPM ends up around 25000. The reason for this choice is simply that 25000 RPM provides more thrust, and the components still don't seem to have a problem with this RPM. So why not to use bigger RPM range and get more power. If I designed the pump for 20000 loaded RPM, it would have to be bigger to get the same thrust.

@geekmidget 3 ай бұрын

@@mjetdevelopment I purchased a Rocket 4074 with 1700kv and a water jacket, how many amps do you estimate that would draw with the supersprint drive, both for 4S and 6S? The idea was using the motor mostly with 4S while still allowing myself the possibility of using it with 6S occasionally.

@darkokatrasnik9810 6 күн бұрын

Can I use 3660/2600 KV motor and 90A ESC in Supersprint? What battery do you suggest?

@mjetdevelopment 5 күн бұрын

@@darkokatrasnik9810 The KV is a bit too high, 2400KV would make a good 3S setup. You can still run 3S, maybe 3S 2400-3000mAh but pay attention to how hot the ESC will get. Lower KV would be better and then you could run 4S for example. Please follow the Supersprint manual for the most detailed up to date information: drive.google.com/drive/folders/1f-epKNBlcqGcuJU5rGvYQleL7ayPnrRe?usp=sharing

@michalczerwinski9005 2 ай бұрын

Hi, thx for the video - really good stuff. Quick Q it is really hard to find 36xx motor with 1400KV (for 6S) 2100kv (for 4S). and in the set proposed by RC Printer there is "Surpass Hobby 2150KV Rocket RC 3660 Brushless 4 Pole RC Boat Motor" offered. With what battery it should work as it not fit to the table? :) I found 3660 2150KV instead - will it work with 4S? please mike

@mjetdevelopment 2 ай бұрын

Hello, the 3660 2150KV motor on 4S is still ok. It is just slightly above the recommended value but still efficient and safe to use. The electronics offered by RC Printer were discussed with me and I find them to be a good choice. You can also use this setup on 3S for more runtime.

@HonzikTac 4 ай бұрын

Ahoj, Did you tested how long can you ride with the boat (Supersprint)? With your recommended setup - 3660/1400 KV with battery 6S 1200 mAh? Thx

@mjetdevelopment 4 ай бұрын

@@HonzikTac :D really depends how you drive. I had one run where I pushed throttle hard non-stop and it did not last longer than 2 minutes. Also maybe because my battery is getting old. But with less agressive throttle I get 5-10 minutes.

@NikitaCha 5 ай бұрын

Hello. Can you tell what sort of waterjet pump you use in the thrust measuring setup?

@mjetdevelopment 5 ай бұрын

That's pump of the Supersprint: www.cgtrader.com/3d-print-models/hobby-diy/other/m-jet-sprint-3d-printable-rc-jetsprint-boat-model

@skysurferuk 6 ай бұрын

I'm noticing a trend. These deep dives into technical subjects are being done by guys, obviously not having English as their first language. Why is that? Are our kids stupid? Not interested in STEM? A great analysis, thanks. Most useful. 👍

@YAhoraTu 6 ай бұрын

less than 5% of world population has English as first language 🤷

@aviatoFPV 3 ай бұрын

Not easy to find a 1500kv 3660, I can find 1750kv though, is it possible it doesn't hit the 90A cutoff when under less load compared to holding the boat still and achieving maximum resistance in the test?

@mjetdevelopment 3 ай бұрын

@@aviatoFPV If you would like to build a 6s setup, I definitely don't recommend 1750kv. Please note that the newest and final 6s recommendation is 1400kv - I suggest looking at the newest version of the manual, link drive.google.com/drive/folders/1f-epKNBlcqGcuJU5rGvYQleL7ayPnrRe?usp=sharing You made a great point - and it is very likely true that when the boat starts going, amp draw decreases, but I am not expecting this difference to be significant enough. I would like to actually measure it in the future, so far I haven't used any telemetry option. Therefore without proper information about this effect, I find that following the results of the static test is the best we can do. Low KV motors are difficult to find. Where are you located? I only have some links for europe. If you can't find one, you can also consider building a 4s or 5s setup. Many people built the 4s setup, performs very well too.

@bman2827 3 ай бұрын

In the latest version of the Supersprint V1 Motor KV chart the calculated RPM for a 3660 motor at 2S and 3S is much lower e.g. at 3S 11.1 * 2400 = 26,640RPM whereas for 6S it's 31,080RPM. Is this intentional or is it an error in the chart? By my calculations max KV on 3S for 3660 motor should be 2800KV.

@mjetdevelopment 3 ай бұрын

Yes, you are completely right about this. The reason is, that on 3S and 2S the required ESC was over 90A - it was 120, respectively 180A, as seen in this video. Such a big ESC cannot realistically fit the Supersprint. Therefore with the latest version, I decreased the KV on 3S and 2S to optimize the power consumption for a 90A ESC. Now the recommended ESC is 90A for 2-4S and no longer 120-180A ESC is required. It will result in slower speed.

@bman2827 3 ай бұрын

@@mjetdevelopment Ah ok that makes sense! Thanks for the explanation.

@jasonrhodes9726 4 ай бұрын

At what point does cavitation inside your impellor start to wear out the propeller? I don't know what the "propeller" inside a jet boat drive is called.

@mjetdevelopment 4 ай бұрын

I call it impeller. I have never observed any wear caused by cavitation on the impeller. I know this happens on full size jet pumps with metal parts, but at this small scale either we don't run the boats long enough to show the effect, or plastic responds differently to collapsing cavitation bubbles, or there is not that much cavitation at all compared to full size jet pumps.

@hooptiej 6 ай бұрын

you just need a bigger esc(more current handling) or to move to 8s (more volts, so youll need less current).

@thatformanet 7 ай бұрын

How about a Super sprint version with the integrated water kettle?

@mjetdevelopment 6 ай бұрын

Some people prefer high KV no matter the cost, so those will literally build one😁

@jamesatkinson7517 6 ай бұрын

The problem is the prop must be changed to a larger prop to make use of the torque in the low kv motor then the Amps will go up. In a hydro boat the bigger prop will change the characteristics of the boat the size of the boat if small will be affected so badly with a big prop it will lift the left sponson and not run to it best hydronic efficiency. So in this situation the higher kv motor and a smaller prop will go faster.

@mjetdevelopment 6 ай бұрын

Good point