Polarity reversing DPDT switch for Fischertechnik

Modeled after the discontinued fischertechnik Polwendeschalter (photo) from 1968. Watch out for the pin layout, it is different from the original.

The snap-action mechanism comes in two versions, one is fully printed, quite rigid and takes much more power to flip than the original . The other uses magnets, its action and feeling is much closer to the original.

Part list:

• 2 microswitches without metal levers
• 2 pieces of uninsulated 0.8 or 0.6 mm solid wire, 15 mm
• 2 pieces of insulated stranded wire, 25 mm
• 2 neodym magnets 2x4mm for the magnet version

Print all parts as provided, high quality, no infill needed, tree supports for the bottom part's grooves and the lever part. Overall you need:

• bottom and top parts, 1 of each
• 2 Bundhülsen parts
• for the all printed version: lever, bridge and snap part, 1 of each
• for the magnet version: magnet version of lever and bridge, no snap part

See images for assembly, the basic steps are:

1. Clean prints from all filament residue. Test if the microswitches can be inserted seamlessly into the top and bottom parts. Test lever for easy rotation with both bottom and top parts. Clean the inside of the lever part from support residue so that the bridge part can slide in between without any friction.
2. Prepare lower microswitch: shorten all legs to ca. half their length.
3. Prepare upper microswitch: bend both outer legs 90° upwards, shorten middle leg.
4. Connect microswitches: use a vise, clamp and/or toothpicks to fix them together. Solder two crossed connections between the output pins, one of them insulated.
5. Prepare wires: solder a 15 mm piece of bare solid wire to a 25 mm piece of insulated stranded wire
6. Prepare Bundhülsen: wrap the wire ends around the printed Bundhülsen as shown. Test them with a ft-connector.
7. Solder wires to microswitches: Solder both stranded wire ends to the microswitches as shown. The connection to the upper switch is delicate, the wire needs to be parallel to the contact, use only little solder so that the ft-connector can be inserted without resistance after assembly with the top part of the case. File off excess solder, if needed.
8. Insert microswitches into the bottom part. Bring Bundhülsen into place, bend wires so that they don't obstruct the lever and don't cross each other. This is important, it is not arbitrary where you place which of the two Bundhülsen.
9. Assemble lever, both variants are a bit tricky, be patient and don't force it: a) fully printed lever: assemble lever, snap part, and bridge as shown, hold it from the sides while inserting into the bottom part. b) magnet lever: insert a magnet into each the lever and the bridge part. Orient them so that they push against each other. Use super glue if needed. Watch out during assembly, the bridge part is not symmetrical. Orient it so that the magnet is closer to the right hand side where the microswitches are. This is needed to compensate for the resistance of the switch actuators. Hold all together from the sides while inserting into the bottom part.
10. Carefully snap the top part in place, particularly watch out for the Bundhülsen and the central axis.

Category: Construction Toys