THAT IS SO NOT SAFE!!!!!!!
You realize when you 'ride' a robot, your putting your life in the hands of a servo loop which depends on just ONE encoder to give feedback about the motor's position. The loss of an encoder, with today's high high update rates (some high as 20KHz (standard yaskawa servo modulation frequency)) integrator windup happens in the blink of an eye.
So... that effortless power that lifts you up in the air and makes you giggle... could also just as easily slam you into the ground at ~50mph. I may stick my head in a CNC machine... but thats as far as i'm willing to trust a servo. Heck, 'fly by wire' steering still has a mechanical override... automakers know servos are too risky for something like steering. Its just that people who make these robotic coasters havent put the 'what if it hits a bus of nuns' test to their robot coasters like the automakers have.
Sorry to be all uptight... but i've seen an Adept 4 axis arm lose an encoder at work... JT1 (the main joint) spun around 2 times in about .5 seconds. If anyone would have been in the cell they would have been dead (not just dead, like DEAD)... and that was just with people in the vicinity of the robot, let alone RIDING it. I know its tempting... servos are so good anymore it makes the motion seem so serene and controlled, but remember, in free range, theyre just motors.
PLEASE don't do this... ok i'll get off my soap box now.
-q