Horizon Express: Power Function to 12V conversion

[Heppeng]

I wanted the Horizon Express to run on my 12V railway. The easy option would be to stick a 12V motor under it, however they are only available second hand at a price two or three times higher than a new Power Functions motor, and you can't fit those nice decorative sides.

So I chose an alternative, which in fact is pretty lego friendly (only one cheap lego part was modified)

I bought the Power Functions motors, and the short extension leads. Each extension lead was cut in half, and the two center wires soldered to brass strip. The brass strip was then bent and stuck with double sided tape under one of the bogies. This is the end result:

Now I'll admit that it is somewhat crude, but it does work very well, at least after getting the hang of soldering the wires so there is sufficient flex in them to stop them breaking! The sellotape holds out very well too, and should be easy to clean off the lego should the need arise.

It would be better to use phosphor bronze or copper for the pick ups, but I happened to have some brass strip of just the right size handy so I used that.

And before anyone gets hysterical about frying 9V motors on 12V, I did do some measurements with a multimeter to check all was OK, the results being as follows:

With a typical lego train of 1 loco/2 cars -

Voltage at which a 12V train tips on corners - 10V

Voltage at which a 9V train tips on corners - 7V

So my 9V motors won't even see 9V - let alone 12V if I want to keep them on the tracks!!

[zephyr1934]

Cool! How does the pickup do over switches? As for frying PF motors, that not a big deal, it is the insane price of the 9v motors with the metal wheels that I'd be cautious off.

[Heppeng]

It does just fine over switches - the brass strip is similar width to the original 'sleepers', so it does not fall off the side on corners, and as long as the distance between the two ends is greater than the dead part of the switches it will perform just as well as the original 12V system. You do have to make sure that the ends are turned up a little to help them ride over the gaps and rails, but thats all.

Yes, its the insane price of old 9V/12V motors (or indeed the complete cost of the full PF kit) that made me take this route.

It is interesting to note that voltage aside, the 12V and PF motors have very different characteristics, the 12V motor seems to be much more torquey and does not slow down on hills and curves nearly as much as the PF motor, which on the uneven and slightly sloping floor of my old room means the train can be crawling round the curves whilst hurtling downhill on the straights almost too fast for the next corner!

I have cured that by using a Hornby controller which has feedback, ie it measures the speed of the motor and adjusts its output to maintain that speed, so now my freight train can trundle sedately around the whole circuit, whilst the Horizon Express can maintain high speed without slowing down! I do wonder if that means that the standard PF module incorporates feedback to maintain motor speed, and thus allows lego to use a simpler cheaper motor?

Edited September 26, 2013 by Heppeng

[zephyr1934]

I have cured that by using a Hornby controller which has feedback, ie it measures the speed of the motor and adjusts its output to maintain that speed, so now my freight train can trundle sedately around the whole circuit, whilst the Horizon Express can maintain high speed without slowing down! I do wonder if that means that the standard PF module incorporates feedback to maintain motor speed, and thus allows lego to use a simpler cheaper motor?

Nice solution! And no, Lego doesn't use feedback, they just assume you are a child running a light train on a small loop and don't need to worry about such things. I have a couple of really heavy PF passenger trains that have to go too fast on the straights to make it all the way through the corners. It becomes a very tricky balancing act to keep the trains on the track AND going around the entire loop. With 9v it is even more challenging since a large loop (say 12 baseplates per side) will have significant resistance in the track joints.

[Heppeng]

I suspect that a feedback controller may also counter the effects of voltage drop - since there is virtually no current flowing when the controller is measuring the back emf of the motor, there will therefore be almost no voltage drop during measurement even if there is a comparitively large resistance between the motor and controller, and the controller will still see the motor slowing and bump the volts up to compensate.

I got a cheap controller from ebay to try and see what difference it made, and the result was that it made a really substantial difference!

The one I used was a Hornby R965, which is reviewd here as well as others:

http://www.scottpages.net/ReviewOfControllers.html

[zephyr1934]

Wow, that last link was a neat little read