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...