Are these cheap chinese ballnuts doubles like the Zapp DF1605 at £44 ?

That would give about 10 microns backlash until it beds in, but with a bit of Belleville jiggery pokery you can get that down to around zero microns.

Transformers are okay until you get a mains surge and everything goes pop. Unlike back EMF from turning a motor, I have personal experience with this little snag :naughty: