Not as good as the multi-copter, but maybe more practical.
Who needs a Segway or a multi-copter when
while (true)
{
Serial.println("By this time next year practical personal jet packs will be available");
for (int days = 0; days < 365 ; days++)
{
delay(24UL * 60UL * 60UL * 1000UL);
}
}
Please note that the code and the claim it makes are untested.
Rather than a lawnmower or quadcopter - on a more practical level...
Check out the Modifed PowerWheels Forum - do a bit of searching around, and you'll eventually find more than a few projects where people have made their PowerWheels vehicles radio-controlled.
They do this so that they can let their really young children have fun "driving" a PowerWheels car, while still being in control so that the kid doesn't get hurt. They then use them to give them a bit of control for their kids when they are learning, or to provide "emergency" control when the kid needs it.
For some of these vehicles, they have modified them to be much faster than stock, and its very easy for the kid to go out of control.
Building such a vehicle - but larger to carry an adult rather than a child - is doable, but challenging. You basically will have to do everything from scratch - or, if you have the cash - purchase an old adult-sized gocart and convert that to radio control. You can also do the same with a full-sized automobile, but it becomes much more difficult to implement - and much more dangerous to use (don't even go this route - your asking this question clearly shows that you are no where near this skill level to even think about such a project - you'll get yourself or someone else killed or severely injured).
zoomkat:
Look for a used riding lawnmower to modify.
Actually the simplest way would be to get a used mobility chair with differential steering. Strip out the motor controller and joystick (most are near to impossible to bypass or control - proprietary and safety lockouts - all for good reason). Add new batteries and a new motor controller (easiest is a Vantec - or, depending on the wheelchair motors and such - current draw, that is - you might be able to get away with something cheaper).
There are plenty of ways to do something like this. In the link you posted of the RC lawn mower, it looks like they are using electric window motors and roller chains to drive the back wheels. There are motor drivers capable of controlling such motors with an Arduino, or you could home-brew your own like he's done in the instructable. Rubber tires seem like they would probably be the best bet for moving across most surfaces even with the added weight of a person on top. But if you want to get really fancy you can build yourself some tank tracks so you won't get stuck in sand or mud and depending on how you configure your tracks you could even give your vehicle the ability to climb stairs or go up and over rocks.
It would probably be best to start out with wheels until you get the hang of things. After that..DIY Tank drive systems
cr0sh:
Rather than a lawnmower or quadcopter - on a more practical level...
Check out the Modifed PowerWheels Forum - do a bit of searching around, and you'll eventually find more than a few projects where people have made their PowerWheels vehicles radio-controlled.