Feather weight spinner questions

[webby]

I am designing a disc atm, 100mm ally with 2 20mm steel teeth protruding 10mm out.

First thoughts is to use a speed 900 for the drive motor?

If so i've been looking at calculations for the 1kg disc and 3000rpm motor (which is what the seller says)

But what size pulleys would people recommend for that combination?

And is there already a thread about this?

Thanks
Ashley

[Eventorizon]

Unfortunately things have moved on for several reasons over the past few years... (I am assuming you mean a featherweight here)

-Speed 900's are no longer made and are an out dated technology when it comes to spinners.
-With LiPos now becoming the norm this means the weight used for power is massively reduced from NiMHs. All this weight goes into the weapon in a spinner, usually.
- Brushless motors are now getting very cheap, see Hobbyking NTM motors, an spinner with its weight will have a 42mm NTM motor on 6S lipo at least.
-Most spinning weapons are now made from single pieces of steel, either milled or waterjet cut to shape. A toothed aluminium weapon would be ripped a part my a modern style one piece disc.

Most featherweight spinners have a weapon mass of around 3Kg + or - 1Kg, most of the time. They use a brushless motor on 5S up to 12S to get weapon RPM's in excess of 6000rpm (as much as 13'000 in the case of 720) and range from 98mm dia drums up to massive 400mm discs. The tip speed, or the speed it would travel if the disc was a wheel, is usually 250mph+

Just a note: this is all relative. The robots shape, weight, size, drive needs, armour and the weapon mass, diameter, bite, speed make each system unique.

As an example: 720 has a 3.5Kg, 98mm drum doing 13000 rpm but uses an inrunner on 5S.
Conker 3 was a 160mm whisk doing 11'000 on 12S with a mass of 2.2 kg.
Drumroll is around a 100mm dia weapon, Weighing 3Kg and doing around 8000rpm...

[webby]

Right ok. Thanks for your help.
So speed 900's are out of the question.
What inrunner motor would you recomend? or what KV?
based on the same disc diemensions and weight?
thanks

[maddox10]

Several remarks.

1 kg disk in a feather is a light disk. Vith 100mm diameter, totaly no optimalisation and heavy teeth, it will be 40mm thick.
I would use a complete steel disk, laser or watercut from the better stuff like Hardox.

Speed 900's are getting very rare and expensive. Also, their nominal RPM is 6600@12V. Overkill on this light disk tough.
We drive a 1 kg 275mm "Trident" with a Turnegy 3650 1100KV Vspeck inrunner in Nebelwerfer. But that's a 6 kg Raptor class machine.

Pulleys. Depends on type of belt used. I prefer timing belt.
The smallest timing belt pulley on the motor will be a T05 with 12 teeth.

There is probably a threat with the information you want.

[webby]

Right ok.
I'll upgrade it to 40mm but I wanted to build it like that as I have acess to the machines for it and I've seen them designed like that before.
Thanks

[webby]

Would a 3300 kv motor work?

[Eventorizon]

The Kv rating of a motor has no relation to its power. You need to look at its wattage, but I will explain Kv first.

The Kv rating of a motor is the number of revolutions per minute that motor well do per volt applied to it. A single LiPo cell is 3.7V. You simply multiply the Kv by the voltage to get the motor speed, so that motor on a 4S liPo is: 3300 * 3.7*4 = 48840 RPM.

What you need to use to determine what you need is the Wattage. For a 3Kg weapon most people use a 2500W to 4000W motor. Conker 3 has the most at over 5000W but that is mainly because the motor was a better shape for the design.

If you just want to spin 1Kg at say 8000rpm you could get away with a 1000W motor. But that is a guess.

http://www.hobbyking.co.uk/hobbyking...00KV_815W.html

^ That would quite happy spin a 1Kg 100mm disc on 4S with a reduction of maybe 4:1 or 5:1.

http://www.hobbyking.co.uk/hobbyking...0KV_2665W.html

^ That would spin it a 1:1 no problem but its more than twice the wattage, its heavier and larger but that motor is becoming the minimum for a modern FW spinner.

But its not that simple. You are balancing a lot of things in a system like this and its unique to each robot design.

[webby]

Ok thanks.
Happy to know what kv actually means aha

Those motors look good but for my design it needs to be an in runner motor?
Any ideas on an in runner motor I could use?

Thanks

[webby]

What about this motor?
http://www.hobbyking.co.uk/hobbyking..._Inrunner.html
Like it as it has enough power and is turnigy, but this one has more power but unsure about it due to no brand and no reviews.
http://www.hobbyking.co.uk/hobbyking...er_1100kv.html

[maddox10]

If you want to use an inrunner, no problem.
If you want to use an outrunner, not a problem either.
It's all in what you can and want to work with.

For disks I prefer outrunners, but I use them rather unorthodox.

The reason we have an inrunner in Nebelwerfer is because the German Raptor rules say "no outrunners".

And yes, RC motors can be very usefull, but if you read a lot of build reports, you'll notice a lot of experienced roboteers adapt those to be more rugged.
Just like we do with Bosch 750's in Heavies.

[webby]

Right ok, good to know.

so which one from the 2 i posted would you recommend?

Im leaning towards the turnigy one as i feel it would be more reliable.

Thanks for your help

[typhoon_driver]

To be honest, you will struggle to get useful recommendations as there are so many to choose from and relatively few have been used by roboteers.

I've solely used the scorpion motors with great success but advice that I would pass on would be, support both sides of the motor pulley shaft. The shafts and casings are not meant for the forces they will see in a combat robot and i have snapped shafts and bent casings on motors.

For such a light disc you will get away easily with either an outrunner or inrunner. Outrunner generally has greater torque, inrunner greater speed. Depends what is needed in your design. I'd recommend increasing your disc size and weight but that's up to you.

Which ever motor you go for, run it at it's highest possible voltage. The difference in current draw of my big scopion when running on 10s vs 6s is dramatic (9A vs over 100A) based on black box recordings I have from the esc I used. This makes a huge difference to the stress put on your esc, wiring and batteries and will allow the machine to run for longer comfortably.

[maddox10]

If you can't "ruggedize" the motors, the best bet is to use one you can replace most easy.

Otherwise, it's budget and creativity.

As written by others, each to his own.
I prefer the NTM range of motors. Affordable and easy to adapt/rebuild.

[webby]

Right thanks for all your help guys.
I am purchasing a Turnigy XK3665-2400KV motor.
2400KV
80A
1185W
But unfortunately haven't ordered it as Hobby king has broke!

Any ideas on the ratio for the pulleys for the 1kg 100mm disc?

Thanks!

[maddox10]

It seems the motor is ment for 4S, and that gives a motor RPM of 35520.

I would go for a 4 to 1 ratio.