Hazbot you are right mobility is important. I personally like the wheel, track design. Easier to work with and they can move about faster. I'd eventually like a Bipedal but too slow and complicated for me right now.

Now this did all start cause the boyfriend wanted to build a quad rotor. I had an idea to turn SPykee into a quad copter then he could move on ground too.

First off, Tracks are just plain cool! They are more difficult to build and require more power to operate, and they are louder. But they can really cover ground and move on most surfaces. I think a good alternative to tracks is a 4 wheel design. You can drive the two wheels on one side with a single motor, but there is less resistance than with tracks so better energy consumption and less power usage for the same output. This is what the omnibots use. You can also do a double wheel drive with a "tail dragger caster" for balance. I think a lot of it depends on how you want to use the bot - indoor/outdoor, smooth/rough surfaces, etc.

When we first started we used the 360 degree rotation servos from the Kit for wheel turning. That was fine - servos are light and can be powerful but they are not good for connecting direct to wheels as they have a very narrow connection (a narrow nylon male cog - no shaft). After a while the wheels would work loose, seperate and drop off. Also the tail dragger caster on the back would mean fine power tuning to the front drive wheels otherwise, while the bot could spin on a dime, his forward direction could be slightly off to the left or right. We then tried electric screw driver motors and all of a sudden we had a lot of extra weight, the additional requirement of a H-bridge and battery issues (more volts and amps needed). A seperate issue was having wheels capable of getting over carpet or bumps in the floor without the robot shuddering. One answer to this is bigger wheels but as soon as you take that option you need more leverage, more torque, more power. To reach our multi-surface goal we ended up where we are now, waiting to apply 1/16 tank tracks to the robot. I've seen toy bots with 3-4 wheels each side but not sure how they work or what the advantages are, also seen cone type wheels that are super flexible but I think would be limited by weight.

These guys are developing a single wheel robot.

single wheel robot

Check out this neat design. Could make a robot like Rosie on The Jetsons cartoon

Omg I want to make a ball balancing robot!

Absolutely - WOW - There must be an infinite number of applications for a ball Robot like that..

I need that!!!!