Need help choosing motors for a ~100lbs robot - Single wheel w/ internal balance

[stridera]

I'm building a robot out of steel with a single drive wheel. The robot will be about 3.5' tall and 1.5' wide.  I need a motor that will support the steel robot in both movement as well as the quick forward/backward tugs to keep it standing upright.

I will also need a second motor (two actually) that will spin an internal flywheel to keep it from tipping to the side. (The second one will help it turn right and left.)  This one requires the high torque/quick accel, but doesn't need a high top speed.

All the motors will need to provide the torque required to handle the quick movements. I don't care about extra speed. (Bonus points if the motors are powerful enough to let me sit on the robot itself and have it wheel me around.)

I'm not too concerned with the price (as long as they're reasonable), so I would like something that is strong and durable. The case is large enough to support a couple 12v batteries and descent sized motors, however, being able to run for a few hours before recharging would be nice.

Drive wheel is ideally 16" diameter, 7" width. A hub motor for the drive wheel would be the best idea, but I can live with an external/chain drive motor if I must. Anyone have expertise on this or ideas where I can go to start shopping? This decision affects my entire design so help is greatly appreciated.

I've looked at bicycle hub motors, but in all honesty I'm not knowledgeable enough about the specifics of the motors to be able to select one.  My plan was to get one with plenty of power and welding it into the rim of a wheel that matched my specs.  This a good plan or is it not advised?  (The other option is to machine the wheel myself.  I do have access to a few CNC milling machines, but suck at designing.)

I'm a programmer by trade, so the actual construction is all new to be, but I'm exciting for the challenge.

[Billy]

All the motors will need to provide the torque required to handle the quick movements. I don't care about extra speed. (Bonus points if the motors are powerful enough to let me sit on the robot itself and have it wheel me around.)

I'm not too concerned with the price (as long as they're reasonable), so I would like something that is strong and durable. The case is large enough to support a couple 12v batteries and descent sized motors, however, being able to run for a few hours before recharging would be nice.

You can get wheelchair motors used on ebay for a reasonable price. They will tear your arm off and are built like tanks.

I'd be interested to see where you decide to put the batteries. Low and it will balance easier but the motor will have to work hard for corrections. Higher up and the motor won't have to work so hard but will need to make longer moves for correction.

[stridera]

I'd be interested to see where you decide to put the batteries. Low and it will balance easier but the motor will have to work hard for corrections. Higher up and the motor won't have to work so hard but will need to make longer moves for correction.

I was thinking of having a steel platform right above the tire that would house the batteries.  Above it will house the flywheels.  If I can get inventor to cooperate with me, I'll post images.  (Or better yet, if I can find an awesome hub motor I'll build the frame and take pictures.)  Until I get the hub motor/wheel, I can't really do much since everything else revolves that.

[stridera]

OK, Maybe if I change my question?  (Should I post this as a new post for visibility?)

I'm looking at this motor right now:  http://www.conhismotor.com/ProductShow.asp?id=78
Brushless Hub Motor 24V 500W for Front Wheel:

Voltage: 24V
Power: 500W
Motor Type: Brushless Gearless Hub Motor
Motor Net Weight: 6.2kgs
Motor Diameter: 24.5cm
Hall Sensor Quantity: 3pcs
Max. Speed: 235RPM
Max. Torque: 23N.M 
Magnet Body Size: 300*136*30mm
Axel Diameter: 1.5cm
Min. Fork Width Requirement: Min.8.5-9.0cm
Corresponding Controller: 24V 500W Controller

So, if you guys could look at this as a teaching moment.  I have no clue if 23N.M is enough torque to handle the reverse pendulum balancing.  How would I figure this out?  I would appreciate any help.  (I've read both pages for choosing a motor, but I still have questions, such as how do I know what torque I would need?)

[Soeren]

Hi,

Drive wheel is ideally 16" diameter, 7" width. A hub motor for the drive wheel would be the best idea,

You can get complete wheels from 12" up at goldenmotor
Not sure about the width though, but perhaps a wheel from an electric scooter.

Why this wide a wheel?

[stridera]

Trying to make a replica of something.  (Claptrap from Borderlands.)