Brushless motor for feather spinner?

[Runsler]

I just wonder, what motors do you guys use in your featherweight spinners?
I know spinners in this class are kinda rare, but there are some, and while looking for a motor myself, i have absolutely no idea what would be suitable.
So chances are good i'd end up with either a really big motor, and almost no weight left for the actual weapon, or a good weapon and a motor too small to power it. And since brushless isn't the cheapest stuff around, i'm asking you what you are using.

[maddox10]

Brushless can be pretty cheap tough.

The motor used in Valkiri 2 and 3, aswell in Surveyor and DX11 was the £40 540 gram Hobbyking NTM5060 combined with the £30 Hobbyking SS190-200 ESC.

I don't think anybody will call Valkiri3 underpowered in the weapon.

[Eventorizon]

Feather spinners are very common, you just don't get to see them at the HW live events, but I can assure you there are more than you think :-)

Sadly the NTM 5060 that Maddox uses is no longer for sale. However you can get the NTM 4258, and that would be more than enough to spin a 2kg weapon on a 4:1 ratio, maybe even 3:1. Use the same ESC and you are off. (Just be careful!)

I personally use a Scorpion HK 5020, cos I am crazy, and my Dad's machine has a Scorpion 4035! But you will find many motors that deliver around 2000-3000W in use.

[Runsler]

Using the scorpio, what drive motors do you use?
Since the Scorpio seem to be made for 12s, while most suitable motors for drive systems are 4s or maximum 5s...
And i'm absolutely not sure if it's a good idea to use two different batteries, would most likely need two links then, too.
And two links just sound like a bad idea.

[Andy]

I use a scorpion 4020 in my featherweight, its quite a bit less powerful than Alex's motors but it runs off 6S so I can use one battery to power the weapon and the drive, while Alex has multiple batteries to give the drive and weapon their rated voltage.

[Danny B]

However you can get the NTM 4258, and that would be more than enough to spin a 2kg weapon on a 4:1 ratio, maybe even 3:1. Use the same ESC and you are off. (Just be careful!)

I just looked on the Hobbyking website, it says the NTM series is an outrunner. Does that make secure mounting difficult?

[maddox10]

Not for me. The front plate has 4 M4 mounting holes.

I reïnforced those with Helicoils.

[Danny B]

One other thing I was interested in finding out. Assuming the weapon weighs around 2kg, what would be a good outer rim speed? I'm wondering what the lower limit would be, since gear ratio and weapon diameter would affect it significantly.

[overkill]

It really depends on the diameter of the weapon. For a drum that might be 100 to 150 mm, a typical speed would be 6,000 to 8,000 RPM (double that if you are Alex). A large diameter horizontal bar might only be 3,000 RPM and still do plenty of damage.

[Danny B]

Ok. As for the motor, do you think this would suffice? https://hobbyking.com/en_us/turnigy-...ner-motor.html

[maddox10]

Valkiri2 had a meassured top speed of 6000 rpm with a 405mm disk. Tip speed 450 km/h .

[maddox10]

That motor is a tad low on power . 18.5V*60A= 1.1kw

[overkill]

That SK3 motor should be fine for a smaller diameter weapon like a drum or a small disk, maybe not enough power for a larger diameter. As long as you gear the motor down, it will probably be fine to over-volt the motor on a 6S pack to get a more power out of it; power will be almost 1.6Kw on 22.2V. With a 2:1 belt reduction and running on 22.2V, the no-load speed at the weapon is a respectable 7,000 rpm.

[Danny B]

That motor is a tad low on power . 18.5V*60A= 1.1kw

Which one would you recommend for a 1.8kg bar, about 300mm across? And what gear ratio? I already know I'll be running a 5s lipo.

[overkill]

It is almost impossible to find a higher powered out-runner designed for 5S; manufacturers have discovered that with new FET technology it is cheaper & easier to make low Kv, high voltage motors. Just a few years ago, it was rare to find medium to large motors for 12S batteries, now they are everywhere and motors above 1.5Kw designed for 6S and lower are becoming scarce.

For a high powered motor on 5S, you will probably have to turn to in-runners like this: https://hobbyking.com/en_us/dt38-620...ner-motor.html. The smaller diameter means they have less torque than a similar power out-runner but that's the compromise you have to make to run at 5S.