Unless they are very small, operating a dalek requires the operator to sit down. The original daleks had a seat built into the skirt section and moved on small wheels casters fitted to the base. This worked fine on perfectly flat and solid studio floors built to support heavy camera and lighting gear but failed dismally on location.
Salvador has a steel sub-frame fitted with industrial costars. This frame is much stiffer than my original attempt to make a frame out of wood. But it is very very heavy and the casters aren't really big enough to move him easily. This is an especial problem at the Boston Westin Harbourdrive where the floors are either carpet or rough cut stone.
[NYI: pictures of frame]
The frame is made of welded steel tubing. This makes it much heavier than it needs to be.
At this point I have only got as far as buying two motors of the type used in motorized wheelchairs.
These might go in a dalek frame or might be pressed into service on a K9 build instead. I bought new as the price was less than the cost of second hand wheelchair motors. But these motors don't have safety brakes which proper wheelchair motors do. That won't matter on a K9 build as there is nobody in him. But it could matter rather a lot on what is essentially a wheelchair.
If I do build a motorized frame it will be multi-purpose allowing it to be used on a Shawcraft or Davros build.