12v DC to 6v DC to run a loco motor. Advice please.

[Chris smith]

Hi, I am scratch-building an N gauge 0-4-4 loco chassis using a small 6v Coreless motor. The chassis build has gone really well. The motor is listed as 6v DC max input and as you can guess is prone to speeding away even on low 12v DC control.  Question, how do I reduce the voltage going to the motor from the pickups and doing it in such a way as to allow the loco to run in either direction as normal.  Most of the hacks I have found on-line are only for devices with a fixed polarity input.  The common solution is Resistors or diodes or a combination of both.  Is there a fix for this which can be made to fit inside the small space remaining in the loco body please? Schematics, diagrams with descriptions or even links to You tube or other web links would be beneficial.  If you have sorted this issue yourself, how did you tackle it. Thanks in advance, Chris. 

[ntpntpntp]

Is there something unique about the size of the coreless motor you've chosen?  Is it significantly smaller than the 12V coreless motors sold by the likes of Tramfabriek and Micromotor.eu?

Resistors get hot. Honestly it's simple, use common sense and just don't turn the knob so far  

I have a railcar with a Tomytec chassis which tended to run rather faster than other models on my automated shuttle, so for that one I use a string of diodes wired inverse-parallel then in series with the motor.  Each diode reduces the voltage seen by the motor by about 0.7v.  It's a bulky solution though, even with SMD diodes but it has tamed the speed to better suit the automation.







I also have a DCC fitted tiny 009 shunting tractor which has a 4.5V motor: for this one I've used a decoder specifically designed to run low voltage motors (I thinks it was either a TCS or a CT Elektronic decoder).

[Chris smith]

Hi, thanks for the reply and the pics.  Yes, the motor has to fit in a specific space hence the size requirement.  The loco works ok providing I don't wind up the control knob too far ! I had found a similar schematic using surface mount diodes but space inside the loco body is sparse so I didn't go down that route in the end as the loco needs weight added to help it run. Wheel for it are another challenge, no greater than 7mm diameter and I need to adapt them for conrods and valve gear.  The nightmare of that is yet to come,      I will most likely just keep the control knob low power and try not to forget to wind it up too far.  Thank you !

[JanW]

Maybe a silly question but could you use a separate controller for this loco?
There must be simple pwm controllers that you can use on 6V.
Put a swith in the track feed to select the right controller and you have a dedicated controller for the 6V loco.

Of course this only works if you always use it on the same track circuit.

Jan