Motor/gearbox for turntable application

[Briefoutcries]

I am working to build a wire dereeler(turntable) and would like to learn how to size components instead of assuming existing machines where built appropriately. I will state my perceptions, based on my limited experience, that will lay a platform for the reader to see what I am missing.
The load is coiled wire weighing 2000#s on a reel that will sit 20" from the center of the table which will have a diameter of 42" consisting of 1/2" mild steel(200#s)
My desired rpm is around 29
I will be using an AC motor with an inverter and a potiometer to allow control speeds from 0-29 rpms
The load can coast to stop as opposed to braking which decrease some inertial problems.
The machine will run about 10-16 hours/day
Chain drive size 50, an assumption on size
Worm drive gearbox 40:1(assumed efficiency 70%)

Desired speed: 30 rpm
Components: motor(1750 rpm), gearbox(40:1), sprockets(4" 19tooth, gearbox output)(6" 29 tooth,turntable center) 1750/40=43.75 43.75*0.667=29 rpm (overall reduction 60:1)
Torque transmitted: load/radius 1100/1.667'=659.87 ft-lbs
Torque inertia: 659.87(29) divided by 308(1)= 62.1 ft-lbs
Torque actual: 722 ft-lbs/0.7 for gearbox efficiency = 1031.4 ft-lbs
Motor input torque of 17.2 ft-lbs(1031.4/60)
Seems like I'm missing a lot here because the turntables I work around use 3hp motor and my numbers point toward something much larger.
Thank you for any insight.

 

[MintJulep]

Torque transmitted: load/radius 1100/1.667'=659.87 ft-lbs

That's wrong.

Your torque is not turning the load. It's turning the friction caused by the load.

 

[dvd]

Torque is probably force X radius (units lb-ft).

Torque might also be related to yielding of material as it is straightened during decoiling, in addition to frictional load.

It is not a constant diameter coil: as material is decoiled the diameter gets smaller, however, the payout speed decreases at the same time. Power might stay constant, but torque probably increases for smaller diameters.

What is torque inertia related to? I assume that this is at constant RPM.

 

[Briefoutcries]

Wow, that's embarrassing, I was going by memory. Yes force * radius, which changes my numbers significantly. Dvd, you are correct the load is not constant and the payoff speed varies by coil size and equipment demand. The 20" is an I.D. measurement of a 30-40" wide coil. I will construct the decoiler with the pot on a pivoting arm that will increase payoff speed as the arm is pulled forward and slow down as the arm relaxes. The torque inertia I got from a paper from a gearbox manu. and yes is assuming a constant rpm.
"Torque & rotating masses. For applications that include heavy rotating masses, additional torque is required to bring the machine up to speed. This would include applications involving flywheels, large conveyor rolls, rotating tables, and rotating drums. For applications like these, the load inertia (referred to as WK2) must also be considered. These inertia loads invariably use more power to start and accelerate to running speed, than they do to keep running at full speed.
The torque to accelerate load inertia (WK2) may be calculated from:
Torqueinertia =
WK2 x RPM/ 308 x time
where:
Torqueinertia is in pound–feet (lb–ft);
WK2 is in lb–ft2 ;
308 is a conversion factor;"