Thanks very much, Roger! That is excellent documentation to reproduce one that will work the first time instead of my usual trial and error system. lol
Wish I could offer some help on the DR chippers. Some of them no doubt do have a "roller feed" mechanism that helps control the amount of material being fed. Very likely the DR website has videos demonstrating the different models. They do advertise on TV too. DR products appear to be high quality and they have been around several years.
The smaller yard style ones like the Troybilt that I use accept smaller twigs, leaves, and such through the large funnel at the top. It has a gang reel of "hammer" like blades that snatch it and beat it into pieces that will exit whatever size screen is being used at the bottom. The small funnel on the side ends at the flywheel which has a few blades, much like a plane, that cuts as you hand feed the larger limbs. The hammer mill inside finishes it. The funnel size controls the maximum size limb that can be fed in.
Needless to say, all of them require full attention and protective face gear as the danger level is high. What ever is stuck in there is gone in a heartbeat!
Let us know what you get and how it works for you.