Micro Helicopter Repair

This page is about repairing my Revell Prion Helicopter, which after several crashes, has a broken gear for one rotor. There is a YouTube video about this, and more pictures below:

Fortunately there are two gears which are the same in this model of helicopter - one which drives the top rotor, and one which drives the bottom rotor. The plan is to make a mould from the good gear to cast a replacement for the other.

Note that I've written to Revell to obtain replacement gears, which they have replied to say are available, although there doesn't appear to be an item to purchase on their website amongst the other spares for this model.

I've put the good gear into a box made from clay which will have Silicone RTV poured into it. I'm using Repsil E30, but any bog standard moulding silicone will do:

Silicone is poured into the box which makes a negative impression of the gear in the rubber. I used Polyurethane casting resin to make a cast of the gear from the mould:

I used a 0.8mm drill to drill out the centre, and then fitted the gear back into the helicopter. It appears to fly fine.