Woodgas stove normally has three stages: (1) lighting it up from the top using lamp oil, camp fire starter, or whatever you see fit; (2) gasification to turn wood into combustible gases (H2, CO, methane, etc.), also know as pyrolysis; (3) continued burning of the leftover charcoal by turning it into CO and burn to produce CO2.
This video shows several trials of maintaining slow second stage woodgas burning with controlled gasification. This is done by introducing another path for the mixed air and gases between the inner burning chamber and outer paint can. As a result, there are two paths for the air and gases: (1) along the central riser and (2) along the empty air space between the inner and outer chambers.
I have achieved success in controlling the woodgas production process, i.e. slow burning with orange and blue flames. However, I have trouble to achieve smooth transition from the 2nd stage to the 3rd stage without smoke. The video by Heath Putnam below shows using transparent glass cup as outer chamber that the top burning suppresses the bottom burning and vice versa:
I had tried drilling more side holes to both the central riser tube and the inner burning chamber close to the bottom. Some improvements seen but not enough to call success for switching the charcoal burning stage without smoke.