Sanity check on traction motor power

[Stepper]

Dear All,

I am trying to run a sanity check on the motor size of the following World War 2 military "turntable" rail system:

- A level, circular narrow-gauge track, with an outside diameter of 20 meters (65 ft)

- The track is narrow gauge (80-90 cm; 30-35”).

- 4 electric locomotives are distributed evenly around the track.

- A weight of 100 metric tons (221000 lbs) rests on top of the 4 locos (i.e., the locos share the weight).

- Each loco has 1 electric motor.

- Each loco has 2 bogies.

- Each bogie has 2 axles.

- Each motor is down-geared and drives at least one axle of one bogie.

- The diameter of the wheels on the inside rail is about 5% smaller than the outside wheels. The inside rail is raised 5 cm (2")

- The axles may have been aligned so as to point at the center of the circular track.

- Nominal speed of the locos: 8 km/h (5 mph)

Question: would 4x 13.5 hp have sufficed to “get the train going” and accelerate it to the nominal speed? How long might that have taken?

Thanks in advanced!

-- Fred

[timz]

100 tonnes on 32 steel wheels... all we know is 100 tonnes on 8 wheels rolling at a constant 5 mph would take much less than 54 horsepower-- a tenth of that would likely suffice. So you can make a fair guess at the acceleration if you know the maximum tractive effort-- do you know that?

[Stepper]

Thanks timz!

What I listed is about the only info that I have. Given the low speed, the part of the resistance/friction that depends on speed or speed-squared, might be negligible. That would leave primarily the friction of the old fashioned bearings.

Here are pictures of the locos:

[timz]

Yeah, that's always a mystery with trains too-- what does it take to get a friction-bearing car moving before the oil has coated the bearing.

[Overmod]

For more on thie FuSAn, go here..

Some information about required speed is here; note that acceleration to operating rotational speed iappears to be relatively unimportant.  Continuous speed is for 12 deg/s, or a rotation in 30 sec (2rpm); that works out to a speed of about 8.3 km/h or 5.2 mph, so there's your HP basis...

[erikem]

Cool stuff there. Some time back, I was thinking of ways of making a large moonbounce array using circular 15" gauge track, though didn't have the land or financial resources to set up such a beast.

As far as power requirements...  A conservative guess for rolling resistance would be 0.3% of applied weight, so for 100 tons that would work out to 600 pounds. At 5mph, 1HP would provide 75 pounds of tractive effort (375/5), so 600 pounds would the require 8 HP. The 600 lb figure DOES NOT include wind forces, though I would think that the designers would take care to have the aerodynamic forces somewhat balanced around the axis of rotation, doubling the HP might take care of that.

- Erik

[Stepper]

Thanks Erik!

So, having 4 x 10 HP motors (somewhat less than 10 HP at the driven wheels due to gearing etc), would have been quite adequate to maintain speed.

Any guess if 4 x 10 HP motors would have sufficed to overcome resistance at stand-still?

Yes, the load is symmetrical about the axis of rotation of the turn-table, so that would balance the wind load.

- Fred

[erikem]

Series motors can produce a starting torque that is much higher than continuous running torque, so I wouldn't think there would be a problem with overcoming resistance at stand still.

- Erik