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Twin motor drive
 Moderated by: W C Greene
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 Posted: Sun Nov 26th, 2017 01:06 pm
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davecttr
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I have a dozen or so locos which have a single motor bogie with traction tyres. they work very well, mostly. A couple of them have trouble pulling long trains of Bachmann stock and I get wheel spin. If other solutions don't work I have the option of fitting another powered bogie to the loco giving twin motor drive. This would be simple to do.

My questions are about the electronics, I use Deltang receivers.

Are the motors connected in series or parallel?

Can I use one Rx or do I need two?

Each motor would be drawing about 300mA on max load, do I need a Rx-65?



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 Posted: Sun Nov 26th, 2017 03:16 pm
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Helmut
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Whether the motors are wired in parallel or in series, is dependent on what you have at hand. The series circuit would require the motors having a nominal operating voltage of half what you employ. When selecting a receiver, bear in mind that you have to take the standstill current of the motor to determine the current rating. Digitrax have a nice section in their FAQ:
>>
  • Check the Stall Current of the Motor
    If the motor's stall current exceeds the decoder's rating you are sure to have problems down the road so, start by using the following procedure to check the stall current of your motor.
  1. Put the locomotive without the shell on a regular DC track.
  2. Attach a DC current meter (ammeter) in series with one of the track feeds. Some power packs that have ammeters are really ideal for this test.
  3. Apply 12V DC power to the track for N or HO. (16V for G)
  4. Hold the flywheel or drive shafts to stop the motor from rotating for a couple of seconds.
  5. While the motor is stalled, measure the current that the unit is drawing from the power pack. Be sure that while you are taking the measurement that the power to the track remains at 12V (16V for G scale) to get an accurate measurement of stall current.
  6. Use the manufacturers' recommendations to choose the appropriate decoder for your application.
Generally speaking, N-scale engines with can motors draw about one amp; HO engines with can motors draw about one amp. Older Athearns with open frame motors and Bowers with Pittman motors draw around 1 3/4 amps. Large scale engines (O, S & G) vary in current draw and some even have two motors, those with can motors may draw less than 2 amps but each should be tested individually to determine which decoder to use.
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Last edited on Sun Nov 26th, 2017 03:17 pm by Helmut



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 Posted: Sun Nov 26th, 2017 07:03 pm
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bobquincy
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Motors in series do not share the voltage equally, if one is stalled the other gets (almost) full voltage. Parallel is better but even better is driving each motor separately from it's own PWM driver. Two receivers can be linked to one transmitter although this gets expensive. Another option is to drive a secondary PWM driver from the output of the receiver.



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 Posted: Sun Nov 26th, 2017 08:42 pm
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Helmut
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@bobquincy
sorry to disagree, but what you say is true only when there is BEMF motor control. We are talking about an unregulated PWM output where it doesn't matter at all provided the motors are of the same manufacturer and type. When they have different characteristics even a separate unregulated PWM wouldn't help in any way.
I have driven 4 axle-hung motors rated 24V/800W apiece with one single PWM controller in a 7.25" gauge loco - where I built the necessary electronics myself.

Last edited on Sun Nov 26th, 2017 08:45 pm by Helmut



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 Posted: Sun Nov 26th, 2017 09:06 pm
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bobquincy
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@Helmut,

no need to worry about disagreeing, I am ok with being corrected! 
:)  My only experience with this was a dual motor slot car that did not work well at all (and was analog voltage control).

boB

Last edited on Sun Nov 26th, 2017 10:57 pm by bobquincy



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 Posted: Mon Nov 27th, 2017 06:14 pm
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Budd
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I'm with Bob on this, I am playing around with twin SPUDS under a loco, both brand new, I wired them in series thinking that might be good thing for slow speed control (which those SPUDS aren't renowned for), but one motor was drawing all the power and the other sluggish, if one slipped the other was just dead in the water, that varied over the motors so it wasn't as if one was a dud.Wired them in parallel and they have been ok, not great though, just ok, I am not a fan of SPUDS, they do appear to be improving with some running.I have been using the deltang RX62 and a 9v step up regulator from 1 cell LiPo, initial testing is going good, I have to admit it isn't the best but I shall persevere.
Wayne from Oz



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