# Voltage Regulation Of Toy Train

#### neiji

Joined Jul 25, 2007
19
I have been recently asked to try to maintain the speed of train (3-6V)when it moves round a curve surface.

It speed should approximately match the speed of the linear path before it reaches the curve.

i found that there is a voltage drop when it run round the curve path, this may account for the lost in speed.

How am i suppose to regulate the voltage, taking into account the the radius of curve/circular path, a ramp?

What electrical component should i use ? Detail explanation would be helpful.

#### DSuliuno

Joined Jul 10, 2007
8
1: Firstly, when the train goes around the curve, there is more load on the motor, since the force that it is applying is being 'resisted' by your centripetal force. So the faster it goes, the harder it is to push. It would probably be this extra load and hence current drawn that is causing the voltage drop.

2: Are you using batteries or is the train powered by a transformer? Batteries would explain the lack of deliverable power (due to current delivery capability), and could possibly be solved by putting another bunch of batteries in parallel to deliver more current and reduce the problem of the voltage drop.

3: If it runs on a transformer, I presume it would be powered by a pair of rails under /forming the tracks. If this is the case, you could perhaps make another power supply that delivers more voltage to the curved section of the track and isolate the straight from the curved parts (being careful not to burn out the motor)?

#### JohnnyD

Joined Aug 29, 2006
79
Hi,

I've done a fair bit of research into feedback controllers and there are 3 different ways to go:

SCR/triac like the old gaugemaster controllers
Op-Amp back emf-feedback
Clamping the output voltage to the input voltage using BJTs

The first 2 measure the back-emf produced by the motor and adjust the output voltage accordingly. This only works if you have an un-smoothed DC supply as it uses the short period of zero volts to measure the back-emf. I don't know how the last one works but I remember the schematic didn't use any smoothing capacitors. It is generally a good idea to use unsmoothed DC for small motor controllers as it helps slow speed running. It is similar to PWM controllers but less damaging to the motor. I say generally because any kind of pulsing controller cannot be used with coreless motors (like the Portescap motors), but these are usually only used by people who build their own kit locomotives. You won't find them in ready-to-run locos like Hornby or Bachmann.

Here is the schematic for the old gaugemaster controllers (and also an op-amp based back-emf feedback controller):
http://www.scottpages.net/UniversalTrainController.html

Here is a really good op-amp back-emf feedback based controller which I have made myself and can confirm it works well, plus Anthony is a really helpful guy to talk to if you have any queries.
http://www.webtech.co.uk/controller/

And this is part of an old schematic I found in my dads EM-Gauge society newsletter which uses a BJT to clamp the output voltage to the input voltage. I don't know how this one works and I've never made one but the schematic uses very few parts so would be simple to build. (I can try and dig it out again and draw out the whole schematic if you want?):
http://img.photobucket.com/albums/v330/agua-moose/Electronics/Feedback.jpg

Hope that helps.