K4 motor and pulling power

Overview:

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)

Experimenting with the stock motor, 11:1 gearing:

New motor, 1:48 gearing

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

http://www.gscaletrainforum.com/index.php?/topic/1063-upgrading-an-aml-k4/

https://www.alliedelec.com/product/ametek-pittman/gm9236s020-r1/70050412/

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: