Firstly, some sprung buffers. The photo shows an original whitemetal casting (rear), and a bored out casting (middle) and a couple of steel heads and a buffer spring. All done on a lathe, the castings were bored after making a split collar to hold the casting in a collet. The spring is 36SWG phos-bronze, wound around a 1mm dia drill bit. The fat end of the buffer is 2.4mm dia. The buffers don't yet show the cross-drilling (0.35mm) in the thin tails (0.8mm dia) for the locking pin which fits behind the buffer beam. There is one pin for each end of the loco, which goes across the buffer beam, and through the shanks of both buffers.
Secondly further video of the loco uncoupling with the DCC controlled AJ's. As shown on earlier blogs, this is the first 4mm loco built with the couplings in mind, which was a lot easier and neater than retro-fitting. Chip is a Zimo MX620, activating F3 causes the entire "backup, uncouple, pull away, stop" routine. There is still some more electronics to add; a bank of capacitors to provide power over dirty track, and I've started to consider lamps fed by fibre optic.