Swing mill electric motor build

[still at it]

Good afternoon Gents.
I'm looking at starting my swingmill build within the couple of months.
I will be purchasing a three phase 20hp 15kw motor. I'm looking at a straight fix arbour to the motor shank. I'm cutting mainly Douglas with a little oak and chestnut.
I need to cut around the 8" (200mm) . I'm thinking of buying a 12" blade to take the constant stress off it.
After reading articles on this forum about saw rpm and travel speed is there anyone else out there who has actually built and running one with a blade and motor of the simular size.
Does it cut efficiently. 
If there is anyone else who can point me in the right dirrection regarding blade size to rpm on an electric motor.

[Gearbox]

That motor is going to be HEAVY . Is there going to be help to turn it [hyd.] ? 20 HP 3 PH. 150 to 200 pounds . Is that a 3600 RPM ?

[Crusarius]

if you can balance it right that should not be to much of an issue. Can also use springs.

[still at it]

It will be balanced to make it easy and I am thinking around 2150rpm so it's not to fast on the blade.
At a later date I will make it power driven.

[still at it]

Springs sound interesting

[TKehl]

Are you planning an 8" max cut?  If so, your motor is much larger than needed.  Electric motors can generally be sized at about half the nameplate HP on a gas engine.  Lucas tops out at 30 HP gas on both their 8  10" cut machines.  So 15 HP electric could be a real good size.

I would also avoid direct mounting the blade to the shaft.
     A.  Belt drive absorbs a lot of shock from hitting a knot or foreign object in the wood.
     B.  Direct drive would mean you would have to adjust the motor mount to adjust the lead on the blade, not a bit deal, but I could see this being finicky.
     C.  A belt drive is cheaper than using a VFD to turn the motor speed down, plus you keep the full capabilities of the motor without concern for VFD derates.

[still at it]

Maximum cuts will be 12".    The majority of cutting will be 2 × 8.
Thought about running the large blade a little slower with a higher torque when running into knots