Dog gears dont spin anything up, they simply replace the syncro rings in a standard gearbox and rely on the engagement slamming into each other one side has a castliation the other is machined to accept the castleation with a degree on elonagation to help enagement, unlike a standard syncro cluster which slows the hub down before carrying out a smooth enagement.

There are numerous configuarions of dog boxes and some work better than others....as an example quaife used a large 3 dog change then evolved to a 6 dog to try and improve change quality....number of dogs, quality of material, design of the cluster all go towards improving the operation of a dog box.....

They operate in exactly the same way mechanically whether they are sequential or H pattern.

Dog boxes require a high level of maintenance as the dogs wear, but they provide substantially less loss of engine power transfer than a standard as the change is carried out without having to slow the box down to change gears...

HTH

Ian