Ultra Low KV Outrunners

To all the brushless guru's. Anybody play around with the new breed of low KV motors made for multi-copters?

Like this one: Rctimer 5010/14 360KV Multicopter Brushless Motor

ST

 

The 400kv's that Ming, Myself and maybe a few others have been using seem to work just dandy, these look like have potential, just not much protection to keep stray crap out of the important bits.

 

Do you have a link to the 400KV motors? Also, which ESC are you using? Are you direct driving the props? What size props? I'm looking for a tested solution for my QE.

 

I'll second that request.

 

Motor:
Turnigy 4258 Brushless Motor 400kv
It's a big motor, tons of torque.

ESC:
HobbyKing® ™Brushless Car ESC 100A w/ Reverse (Upgrade version)
or
HobbyKing ® ™ Brushless Car ESC 60A w/ Reverse

Gears, I've never been a fan of direct drive, it might be a little easier and a tad quieter but gears are overall better. Bismarck has a 2.4?" main prop. I think that or similar is what Ming used on his NC.

 

I put a 390 Kv motor in my 24" rescue boat. Turnigy Multistar 4225-390Kv 16Pole Multi-Rotor Outrunner I used 2 LiFe cells and a 55mm prop (~2 1/8"). Amp draw was pretty low and I had to keep the throttle at about 50% or less to avoid swamping the back of the tug. The motor was very smooth and had plenty of pushing power.

 

YMMV
I offer an example that may be closer to a QE setup:
My Nagato has relatively small props at around 1.325 inch diameter with a lower effective pitch, so I have to spin them a bit faster than SnipeHunter. I'm using 2:1 gears and the same ESCs but couldn't make speed with the low KV motors he uses and the props I have available. I settled on
Turnigy 3648 Brushless Motor 1450kv
for my ship, which runs the two props at up to three times the speed of SnipeHunter's single kort prop. I have flat-bladed props with symmetrical forward/reverse thrust, and have measured the speed both directions last year, it took 62% forward throttle and 100% reverse to make speed (Guess that's one reason why the boat designers don't usually put props in the bow). The motor KV you will need really depends on the effective pitch of the props you use. Pitch measured in inches of advance per revolution, not the 25 or 40 degree blade angle.

 

I ran 400 Kv motors on a NC running 14 volts direct drive with Huge Bronze props (2.6") interleaved and she would do a 12 sec 100' easy.
The get up and go was unreal, and when you slammed it in reverse it would lift the rear end and dip the bow and ZOOOM in reverse.

it would also pull about 30 amps per motor and that is just insane, went back to 970 motors on 12 volts and power was more reasonable.

That said I don't like direct drive and brushless motors, gear box and bronze props and 3/16" stainless shafts with no dog bones in the drive line is the way to go. Brushless has so much torque that it will snap nylon dog bones in half with ease.

 

Stock Drive Products, is a good vendor for drive line parts, expensive shipping is the only downside.

 

Thanks for the input everybody. I've decided to keep things simple initially and since I have a bunch of brushed equipment laying around, I'm going old school for the initial build on the Barham. I'll set it up so it can be easily upgraded in the future.

 

If I were to do it again I would use 5 mm shafts (Amazon) and 5mm gears from ebay or your local Hobby Store. Down side of that is that you have to deal with
Amazon (Small Parts, no service) and they aren't very good at small parts at all, sad they once were good.

 

I'll be using 1/8" SS shafting which can be upgraded to 4mm easily enough if/when going brushless. I've got a cool idea on the shaft seal and motor mountings which I think Mr. Ming will like. Pics sometime next week!

 

1/8" is way tooooooooooooooooo light to swing anything larger than a 1.4" prop, rocks don't yield.

 

In that case I suspect the cheap $3 nylon 1.5" tug props I'll be using will yield first!

 

I have a small issue with my brushless...

I am going to use 2 - 1400KVs .

I can go direct but would prefer to go geared.

Issue is the the largest gear I can put on the shaft is about 19 to 21 tooth, 32 pitch.

I have those on the shaft and would like to run the motors turned backwards, settin on top of the shafts. This gives me more room under my stern guns.

Problem is if I turn the motors where the drive shaft is pointed to the bow(backwards), the smallest gear I can use on the motor is about 42 to 52 tooth.

This gives the boat a 2:1 ratio... I think it will have too much cavitation. I can turn down the end point along with drag props to get down to speed, but I am worried about the 2:1 ratio..

Any thought?

Should I just turn the motors back around and go with 1:1 ration gears....

 

Am I reading that right? You will end up increasing RPM by 2? If so that is way too much speed even for a small prop. Direct drive would be much better, although even there I would not go above a 1.25" prop on 6 volts. Maybe you can find some small belts that would allow you to have a 1:1 drive or even a slight reduction.

 

The problem isn't clearance of the gearbox...it's clearance between the prop shaft and the bottom of the boat

One of the reasons he wanted to fold the geartrain was so the outrunner motor wasn't directly under his guns (spinny-bits rubbing against hoses & brass=bad). I think he's now decided that this boat will be direct-drive brushed motors, which negates all the issues at once.

Oh, but I so wanted to see a VU w/ a 2:1 geared drive. Cigarette racing Dreadnought, anyone?