How much does the rpms matter on an motor for HO scale, I am looking for a motor to put in some old engines, AMH steam hudsons, have found some but they have rpms of around 4500 to 6500. Any thoughts.
The RPM of the motor will participate in determining the top speed of the locomotive. Max RPM, ratio of gear box(s), and finally driver diameter all work together to determine the speed. More importantly might be how much torque it has at low speeds in order to get the locomotive/train moving.
I think the AHM/Rivarossi Hudsons have a gear ratio of around 10:1, which is very fast for steam engines, so the lower RPM motors you’re looking at should work fine. I believe the Rivarossi motors run somewhere between 9 and 10,000 RPM, giving the engines a top speed of around 150 scale MPH, so a 6,500 RPM motor should bring it down to a more realistic speed.
I recently discovered that Mabuchi CD spindle motors are near drop-in replacements for the smaller Rivarossi motors. Here is one installed in an old U25C with minimal modification to the mount. The screw holes even line up.
They tend to be almost as fast as the original, but they’re smooth and silent with good low end control. You could install a NWSL regearing kit in conjunction with the it, or if you’re using DCC you can adjust the max voltage delivered to the motor. They’re available here: http://www.allelectronics.com/cgi-bin/item/DCM-230/400/DC_MOTOR,_1-6VDC_.html
I like the CD drive motor idea. I’ll have to keep a lookout for dead CD drives.
As far as DC motor RPM goes, it is about the same, and it doesn’t matter all that much. DC motors are rated for RPM under no load at rated voltage. Put any sort of load on the motor and it slows down, often quite a bit. For HO or N scale locomotive use, we want a 12 volt motor, but anything from 6 v to 18 v can work. The rated RPM at no load doesn’t mean all that much 'cause a locomotive motor is always under load; the friction of the gears and U joints and axles is a serious load. The maker of the motor controls the no load RPM by varying the diameter and length of the armature winding. He selects something that keeps the motor RPM down to a reasonable value, so the unloaded motor won’t fly apart from centrifugal force, but we railroaders don’t really care, 'cause we never run unloaded. We railroaders want a motor with lots of torque down at low rpms, so the train can creep forward and not stall out when it hits a tiny obstruction. The locomotives have some gear reduction to increase torque. But the gear ratio is set by the locomotive manufactuerer and we modelers seldom change the gear ratio, that falls into the “too hard” basket for most of us.
So, we can use any motor that
- Fits into the locomotive
2 . Is rated somewhere close to 12 V
- Has the best (highest) torque we can find.
Torque is seldom stamped on the motor data plate, so short of finding the detailed spec sheet on the maker’s web site, we don’t really know what we are getting when we start to remotor. We do know that motor torque is proportional to the strength of the motor’s magnets, and the amount of current (actually ampere-turns) the motor has. Can motors are superior to the old open frame Pittman motors 'cause they use ceramic magnets
As to stall torque thats one thing i like about NWSL’s website,it list the stall torque for all their motors, along with all other pertinet information.
Here is the spec sheet for the RF-310T-11400: http://www.mabuchi-motor.co.jp/cgi-bin/catalog/e_catalog.cgi?CAT_ID=rf_310ta
They run a bit slower than the original motors (of course the old motors could vary widely), and have decent torque. I can’t stall the U25C. The 5.9V rating on the side threw me, but that’s a nominal rating, so they run cool at 12V. They have precious metal brushes instead of carbon, so they spin very freely. I tested one with a flywheel and it spun for a long time after the power was cut. I even put one in an old AHM C-Liner that has sentimental value to see what would happen, and it’s quiet now except for some gear noise.