If you aren’t looking to build your own models or just looking to easily expand your collection, there are quite a few radio controlled vehicles available off the shelf. The Siku Control 32 series is very good and I highly recommend the Orlandoo kits which allow you to assemble your own top quality 4WD RC jeeps.
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RC Vehicles
Siku Control 32 Models
The Siku Control 32 range are the best off the shelf RC tractors you can get.
RC Excavators
There is a fair few RC diggers available but not much in 1:32 scale. Kyosho from the Japan make some nice RC excavators.
Diecast Models
Diecast Siku Models
Siku make a good range of static diecast models which are quite affordable but still have good quality.
Diecast Britians Models
Another affordable brand of diecast model. The detail is not as good as Siku and they are much harder to convert to RC.