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low speed and heavy loads: direct drive or gear box?

438 Views 1 Reply 2 Participants Last post by  remy_martian
Hello All,

New member here. Iam a miniature train Hobbyest (1/4 scale, 12” gauge ), new to the EV world. So doing a lot of homework and planning to hopefully restore and convert two or three of my legacy, park gauge (ICE) locomotives to electric motive power.


These are old, 1950’s era park gauge trains that were originally powered with 4 cylinder Wisconsin 16 hp gas engines. In that configuration they would pull up to five passenger cars with a total of 40 adults. I hope to restore them as “ET’s” - electric trains.

So far, I have initially sourced some 9” series wound forklift motors and controllers, and have worked out the requirements for the max safe operating speed, max train weight, tractive effort and train resistance etc for the train consists.

Unlike automobiles, my maximum safe operating range is slow and heavy:
  • train speed: 5mph - 10 MPH max.
  • max overall train weight: 10,000#, (30 passengers, riding in 5 rail cars, pulled by a 1500# locomotive)
  • operating: 8 -10 hours per day.

FYI, the tractive effort metrics for a 10,000# train consist, on 12# steel rail, are in the neighborhood of:
  • total train resistance = 310#
  • locomotive tractive effort (@ 1,450# on drivers) = 362#
  • axle torque (6.5” OD drivers) = 1080 inch pounds at 517 RPM (max train speed of 10MPH)
  • Tractive Effort: individual 9” series wound, 48v forklift motors, (over clocked to 72v maybe?) for each truck (set of 2 drive wheels and axles)

I plan to power each set of trucks (each consisting 2 axles and 4 drive wheels, springs and brakes, mounted in side frames) with a separate, DC series wound forklift motor.

So what Iam pondering, is: will 48v-72v 9” DC series wound forklift motors successfully move an 8,000#-10,000# train weight at consistently slow speeds (5-10 MPH), without melting down? Or do I need to add 5:1 or 10:1 gear reduction to accommodate my expected drive wheel 517 rpms ?

( I assume a direct drive design at such slow speeds will only draw around 20 volts and risk stalling with such a large load.)

Thanks very much for advice you all might be able to offer!

Glenn B.
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I'd put a speed reducer in to reduce max rated motor speed to 600-700RPM (lower is better). Don't forget that your battery voltage will drop, which is a roughly proportional motor speed drop...

I'm thinking one motor will do the job. More is ok, but overkill - if you reduce with belts or chains, run a pair of drivers (4 wheels, 2 axles) off the same motor or jackshaft, since traction may be your remaining issue.
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