K4 motor and pulling power


From the manufacturer, this loco has a number of problems associated with the selection of the motor, the gearing and the drivetrain.

The effect of this is that it does not pull well. The basic problem is that the gearing is too "high" (low numeric ratio) to keep the loco from stalling under load. This problem is compounded by the motor selection.

I added weight that really helped the pulling power, until I melted down the motor! Turns out that Pittman motors will happily run way into the "danger zone" where they cannot shed enough heat to avoid damage. A sealed motor in our hobby is actually silly, not an asset!

Note: the information on the Pittman gearhead motors is the original part numbers which seem to be gone on the new Pittman site, so I need to update the part numbers.

Motor / power consumption:

This loco has a Pittman motor with an integrated gearhead. The stock motor has an 11:1 reduction ratio.

Pittman motors are very different from the "normal" motors we encounter in G scale. In a nutshell, they can easily draw more current than they can sustain without melting down. The motor in the K4 should not run over about .7 amps for any length of time. So, if you "play" with weight, etc. be sure to measure the amps you are drawing.


Here's some data from Jim Carter: (which parallels my observations)

I ran the amp test on the K4.
Aristo TE [trackside] w/ two charged 12v., 2.2ah Gel cell batteries in series, > analog amp meter [in series on pos lead] > connected to motor [only] on K4.
1st test -  drivers suspended [zero load] yielded 1/2 amp draw through out the speed range.
2nd-3rd test- On track, drawbar tied to the track allowing very little or no movement, TE is rapidly powered up.  Max amps = 4 at begin of slip.  Upon slip, amps dropped to 2amps.
4th test - TE powered up very slowly.  Amps went up to 4, and a humm was heard with no wheel slip.  TE immediately powered down.
5th test - TE powered up moderately.  Amps went up to 4 and wheels slowly slipped and then fully broke loose.  Amps dropped to 2A as before.
Previous outside results using QSI with 12 boxcars on 4% grade [loco on level]. 
Loco did not move at all.  I nudged - nothing.  Nudged about 6in, and loco slowly started trying to accelerate pulling cars up around 12 ft. diameter curve, onto back straight.  Train tries to run away on downhill.
Jim Carter

Experimenting with the stock motor, 11:1 gearing:

First, I found that the motor drew so much current and had so much back emf that my QSI decoders just went nuts. I changed to an NCE D808 decoder, basically the highest current rated decoder in G scale, 8 amps continuous and 30 peak.
I added 5 pounds of lead weight.
Bottom line, it pulled somewhat better, but the Pittman was drawing about 5 amps! (I later found that this motor should not draw over 0.7 amps continuously)
So, it overheated the motor, physically locked it up, and then the execssive current draw melted the NCE decoder.
Here's the web site: http://www.pittman-motors.com/ Model:  GM9234S017-R1  24v dc, 11.5:1 062605

New motor, 1:38 gearing

After destroying the motor, Cliff at Accucraft sent me another motor, this one with a 1:48 gearhead:Low cog, GM9234 E 373, 24vdc, 38.3:1, 082102(date code?)
Wow, the max current draw was only 0.5 amp, no matter how much weight I added or the grade. But! now the loco only goes about 32 smph! Not good for a passenger loco.
Two factors here, first, obviously the gearing is wrong. The other is the rpm of the motor at voltage.
These motors all develop max torque at max rpm, and they are 24 volt motors. Well, after a decoder, these motors are surely not getting 24 volts. Looking at the rpm vs. voltage curves from Pittman, I can see the problem.

Yet another motor, 1:29 gearing

Jim's motor: special ball bearing motor, 15v, K27... from Jonathan Beliez, that seemed to work well for Jim, unfortunately it was a special run for the K27, and not available generally


Another motor, 19.7 to 1 gearing

This is what I think I want GM9413-2 12/24v  04-30-99


Pittman data:

GM9200 series is 9000 series motor with G51A spur gear gearbox.
9234 is length of motor (w/o gearbox) - 2.403 inches
24v motor has max continuous torque of 6.1 in-oz, at 1.75 amps (not clear that this is "thermally continuous"

(again old part numbers)


More notes:

The motor supplied had the 11:1 gearbox attached...
This company has the part numbers we recognize for the Pittman motors: http://www.servocomponents.com/products-gear-motors
9413 -224 volt from from toc....


need the number from jc on both the original and the new one


GM9234S017-R1,,,,,,,,,,, 24VDC,,,,,,,, mfgDt...062605


Pittman motors are now part of Ametek motion control.

Ametek is part of  Hardon Kerk Motion control.

So this link works: http://www.pittman-motors.com but you will see when you go to the contact page, the Haydon Kerk name, and you will have to go there to buy a motor.  https://prototypes.haydonkerk.com/


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