The up/down is by the 3 pt hitch. You get the cutting wheel over the stump
and the wheel is pushed foward thru the stump, then back the wheel, lower
the 3 pt and push thru again. This is repeated until it`s all gone leaving a nice
mixture of wood shavings and soil.
I use an old JD3020 row crop tractor (tall) gets over most stumps. I did see
this grinder on a small kubota; so small in fact the guy had to leave tractor on
his trailer to get over a large stump. Once stump was low enough he unloaded
and finished on the ground. I am sure there is some minimum hp requirement
but I don`t the number. This unit does not use the tractors hydraulic system.
The frame of the grinder is the tank that feeds the piston and is controlled with
a lever mounted on the tractor fender.
The only down side is you get neck strain looking backwards while sitting foward
all day