I'm kind of cross with myself. I've broken one of my own rules. I needed bits for 8 robots. So I bought 8 sets of bits. Stupid stupid stupid. You should always buy a few spares in case of failures. It's not that they are expensive. And you can always use the spares on other projects.
Of course a few were duff, which meant that I couldn't make all my robots. Of course (cunning bear move) the faulty parts were the ones I used last. Fortunately have have friends with similar interests (thanks Ian and Robin) so I was able to grab some spares, which is how come I'm sitting on the train with 7 working robots (I couldn't fit 8 in the case...)