REPOWERING  GUIDE

RPM TABLES

For Popular 12 Volt Motors

During the mid 1970s various importers started selling models with compact efficient motors.  These motors had been developed for tape drives, camera drives, electric shavers and other portable electric devices.  They were readily adapted for use in model locomotives.  Not all of these motors were successful as used.  Some really bad motors needed replacement.  Fortunately suppliers like NWSL, ProtoPowerWest jumped into supply the hobby with replacement motors.  Some importers like Kato, West Side Models and others stocked replacement motors for their models.  In the 35+ years since,   Internet sellers on sites like eBay have added quality motors, sometimes unmarked to the available supply.  Some unmarked, unlabeled motors are included in the table below;  help in identifying these mystery motors would be appreciated.  The motors have been organized by width.  Note: A photo of each motor is linked to the Photo Number in Column 1.

	Brand	Model Number	Shaft Size	Width        mm	Height   mm	Length       mm		MOTOR   RPMs						12 Volt
Photo							Start	2 volt	4 volt	6 volt	8 volt	10 volt	12 volt	Load mA
M-26	WestSideModels    (quiet)	1230	1.3	12.7	12.7	30.1	40	1375	2985	4570	6075	7735	1000	2.4
M-5	Johnson Controls	unmarked	2	15.4	20.2	32	360	1170	2400	3660	4980	6230	7870	8
M-6	Mabuchi	FF-180PP	2	15.4	20.2	32	335	1095	2400	3600	4800	6060	7660	10
M-1	Ebay ??  Double End	unmarked	2	15.4	20.2	32	650	1360	3100	4500	6230	7900	9675	56
M-24	Taneda	1627	2	16	16	27.2	500	3000	9200	13100	18700	23600	24500	41
M-7	Sagami                (quiet)	1630	2	16	16	30	40	1530	3630	5550	7400	9700	12900	80
M-25	Taneda	1630	2	16	16	30.4	150	2000	4325	6650	8950	11600	15000	27
M-13	KATO	HM-5	2	17	20.5	33.2	140	900	3100	4950	6850	8625	10975	52
M-2	Canon                   (quiet)	EN22-R11       CN22 -03	2	18	21.9	32.8	125	1340	2850	4195	5685	7210	8865	36
M-4	Canon	DN-22               CN-22	2	18	21.9	32.9	110	1200	3000	4440	6050	7560	8920	50
M-20	Canon         Double-Ended w/Universal	EN22-712N      CN22	2	18.1	21.7	32	25	1245	2915	4430	5970	7575	9090	40
M-14	Nissei	unmarked	2	18.1	20.8	33	1300	810	1800	2675	3665	4525	6000	12
M-16	Mabuchi	FA	2	18.2	24	30.4	53	1800	3830	6000	8100	10150	1285	76
M-8	Mashima	(2335)	2	18.3	23.5	33	425	1175	3150	4725	6375	8120	10150	56
M-18	Ebay ???	unmarked	2.4	19.4	21.8	39.7	350	1450	3225	4900	6900	8600	11000	135
M-3	Pittman	PG6212A008    10.8 volt	2.6	19.6	22	31.9	275	1010	2525	3940	5350	6720	7750	92
M-9	Sagami	2032	2.4	20	20	32	200	1280	3210	4800	6830	8500	9900	82
M-21	NWSL	20324          Single End	2	20	20	32	465	1205	2765	4475	5950	7650	9225	76
M-22	Mellor	2032           w/Flywheel	2.4	20          25.3	20          25.3	32	100	1355	3450	5445	7520	9360	11400	83
M-23	Canon	CM 22	2	21.7	21.7	32.8	45	1900	4800	7800	10600	13300	15000	120
M-10	Sagami	2236	2.4	22.2	22.2	36.8	60	1215	2990	4850	6510	8300	10100	80
M-17	NWSL	22403	2.4	22.2	22.2	40.2	720	600	1710	2720	3810	4860	6900	70
M-11	KTM	2336	2.4	23	23	36.3	36	810	2185	3600	5020	6400	8460	125
M-19	WI	M7T0726A	3	25.3	SQ	26.4	12	285	1110	1900	2720	3500	4580	62
M-12	Sagami	2835	2.4	28.4	28.4	35.3	600	900	2160	3100	4200	5280	6760	60
M-15	Holland	990412012602	3	29	29	40.5	44	670	1535	2280	3160	3960	4850	13

The motors tested were held securely in a small mill vise; 1/8" heavy foam wrap cushioned the motor in the vise. Power was from a 15 volt rectified AC power supply.  Since most of us operate using rectified AC power; using such a power supply matches our needs more than a straight DC supply like a car battery.  Voltage was recorded using a 4" averaging meter.  A Simpson multi-tester was used for current readings.  Key to the test was a Model TC 802  digital photo tachometer distributed by Meter Depot.  This tachometer utilizes a red laser beam and reflective strips mounted on the motor shaft. Without the strips results varied widely and were unreliable.  At least five tach readings were taken at each voltage and then averaged and then rounded to the nearest multiple of 5.  Start RPMs are when the motor starts to turn smoothly. Some hobbyists think that this a good indication of low end torque, it is included at their request.  Note that one of the lowest START RPMs was recorded for motor M-26 which is the weakest motor tested; it was imported in a few models that were shipped without boiler weights. With the addition of a gearhead it was used successfully in several geared logging locos.

Most Japanese models like the KTM model shown on this page used an assembled brass frame riding on coil springs on bronze bearings on each driver axle.  Early KTM models had an enclosed non-idler gearbox, with typically a 27:1 gear ratio.  Many large drivered engines might have a 37:1 ratio gearbox.   A large KTM open frame motor provided dependable power, connected with flexible tubing to the  gearbox.  The flexible tubing also restricts movement of the gearbox, keeping it aligned with the motor shaft.  While the tubing transmits power to the wheels, it also consumes a lot of energy keeping the gearbox aligned, raising current draw.  The photos below show a non-idler gearbox mechanism connected to the open frame motor by a short length of flexible tubing.  Note: the motor is mounted on an angled portion of the frame to align with the gearbox.

The motor shaft on this model is 2.4mm, a common size on Japanese models.  This is also the worm shaft size of KTM gearboxes.  NorthWest Short Line (NWSL) 2240 can motors also have 2.4 mm motor shafts.  The original MG-KTM frame had a motor mount angled to align with the gearbox.  This angled portion of the frame was milled off level with the bottom of the frame to allow the motor to be mounted level.  Two motor mounting holes (2mm) were drilled thru the frame to attach the motor.  The motor if mounted with a section of K&S channel running the length of the motor.  Since one of the motor mounting screwheads might interfere with the trailing truck it was countersunk into the frame.  The sides of the channel can be spread outward to lower the motor, if necessary.  Extra length 2mm screws were used to attach the motor.  They  pass through the frame, brass channel and into the bottom of the motor providing a strong secure motor mounting system that allows for quick disassembly and replacement.

Notice that the flywheel is mounted on the back of the motor.  This puts the flywheel in the steam locomotive model's cab, where there is more room for a larger diameter flywheel.  The larger diameter  provides a greater "flywheel" or coasting effect to the model when the track voltage is reduced or interrupted.  I no longer press fit flywheels onto motor shafts.  Instead I use a NWSL hand reamer that matches the motor shaft diameter to achieve a tight slip fit  and then use Loktite to secure the flywheel to the motorshaft.  Oil the motor bearing before mounting the flywheel, apply Loktite to the hole on the side of the flywheel that will be away from the motor.  This should prevent Loktite from entering the motor bearing next to the flywheel.  Test the motor/flywheel combination before mounting by running the motor at various speeds while held in your fingers.  The motor vibrations should be minimal, the same as they were before the flywheel was installed.

The new motor, flywheel, and drivetrain are a different profile than the original KTM components; modifications may be necessary to fit the superstructure.  Most of the work is enlarging the bottom for clearance for the large diameter motor and flywheel.  I use a variety of tin snips, files and carbide Dremel cutting burrs.  On models imported with idler gearboxes, the cast boiler weight has a notch to clear the gearbox.  A similar notch was carved using Dremel carbide burrs.  This is best done with the weight out of the model.  If the lead weight rest on the gearbox, interferes with the universal drive, or the flywheel rubs on the superstructure, when tested your ears will tell you that you have more modifications ahead.

I have used several can motors in brass models like those from KTM.  For all but the largest engines I use a NWSL/Sagami 2032 can motor. Originally these motors had 2.4mm shafts and were more rugged and durable than flat can motors like the Canon CN2231.  For smaller engines I used the Canon motor but recently switched to the Kato motor used in their HO diesels.  The flat can motors have 2mm shafts and do not tolerate the larger flywheels I like to use as well as the 2.4mm shaft motors.  For installations limited to small 16mm diameter flywheels these flat can motors are excellent.  For the largest KTM HO steamers I prefer the hard to find KTM 2336 can motors; the NWSL 2240 is a good substitute as is the slightly smaller and less powerful NWSL/Sagami 2236 can motor.