I finally got the Hoverbot set up with a relay H-Bridge. Unfortunately, one of the relays died. But that still gives me enough to demonstrate this proof of concept.
As you can see, the Hoverbot picks up quite a bit of speed when the drive fans are operating. In this video clip, the fans are on for three seconds and off for one. I've since reduced the lift fan's voltage to 4.5V (from 6V) and reduced the drive fans' voltages to 4.5 volts.
There are two problems to addess. The first is that the Hoverbot has a tendency to steer to the left. Experiments indicate it is due to the counter-clockwise spin of the lift fan. I may have to double up lift fans in a future design.
The second problem is that once the Hoverbot gets into a wobble, it won't come out. In fact, the drive fans are no longer effective in wobble. The HoverBot is going to have to detect this and correct it. Either an extendable foot or being able to shut down the lift fan is going to be required.
Enjoy the video