This video shows a toggle circuit made from 3D printed relays:
Here is the circuit diagram:
Here the downward pointing arrows represent 0V, the upward pointing arrows represent a voltage twice that required to activate a relay.
The toggle circuit failed fairly quickly (<100 operations) because relay C is switching the coil of relay A and this causes arcing at the normally open terminal of relay C which welds the contacts closed.
I found that this particular design of relay fails after a few 10,000s of operations even when switching non-inductive loads. Generally it fails by remaining closed after power is removed from the coil. I haven't yet worked out what the failure mode is, but some possibilities are:
- PLA creep, reducing the force that pushes the moving pole back to the normally closed contact.
- Magnetization of the coil nail, causing the pole to stick on the normally open contact.
- The pole nail become loose.