Menu

Electrical layout of the coupler

So we have four wires, thus we need four contact pins on the electrical coupler? No, not that easy.
If we'd do that, we could not change the direction of individual vehicles in our train. To be able to do that, we need to make sure, that the same wires always connect to each other, even when the vehicle is driving "backwards".
Thus, the pin layout on the coupler has to be symetrical. The spring loaded pin on the left hand side needs to connect to the same wire, as the fixed pin on the right hand side.
This is exactly, how the VCC and GND wires will be connected to the coupler. The VCC wires will occupy the upper pair of contacts, while the GND wires will occupy the lower pair of contacts. This way, they can not be mixed up by changing the direction of individual vehicles in the train.

However, the C1 and C2 wires are different. In this special case, it actually fits quite well to have them switched around when changing the direction, the individual vehicle is traveling. Thus, they are not placed symetrical.
Instead, they do not change place on the other end of the vehicle. One wire is on the left hand side of the vehicle, and the other is on the right hand side of the vehicle.

Channel	Colour	Side	State when traveling forwards	State when traveling backwards
C1	blue	left	GND	VCC
C2	brown	right	VCC	GND

When changing the direction of an individual vehicle, the C1 pin of the changed vehicle will connect to the C2 pin of the other vehicles, and vice versa. When the train moves forwards, the power in the changed vehicle will suggest it going backwards. Which is exactly what we want, as the "backwards" of the backwards facing vehicle equals forwards of the forwards facing train.

The tender from below

Pin assignment of the electrical coupler facing forwards

Pin assignment of the electrical coupler facing backwards

Pin placement

Because one of the goals of the coupling is to be compatible with existing couplings, pogo pins must be used. Male-female-contacts would collide with the existing couplings. In addition, the centering by the magnets is not precise enough for such small male-female-contacts.
I tried moving the contacts outside away from the center of the coupler while still keeping the coupler as small as possible and within the width of 2 studs. This comes with various benefits.
The magnet inside of the coupler can be bigger.
Also when coupled with the old spinning magnet couplers, the contact pins are not touching the magnet. Instead they touch the magnet holder, which has an offset from the outer line of the magnet, resulting in the pogo pins not being fully compressed. Compressing the pogo pins costs force the couplers won't have holding the train. It's a small margin, but it's also without a downside. The almost same things holds true with the newer coupler design with the housed magnet. The edges of the coupler are chamfered, exactly where the pogo pins are applying their force.

Coupled togehter with known designs

Housing

The housing is 2 studs wide (16mm) and is as long as the original magnet couplers. The heigth of the coupler is a little lower than the heigth of the new original couplers. Instead of having a pin itself, the coupler uses a pin hole which reduces the precision needed on the print.

Drawing of the housing, dimensions in mm

STL download link.
The "9V" and the lightning symbol can be painted as it is raised.
A future improvement on the mounting of the individual pogo pins will likely be made. But in a fully compatible way.