You can't use the HD servo as a drivetrain servo. It has a limited range (180 degrees(?)). You could, however, use the continuous rotation servo. It has a torque limit of 6.5cm. A motor would work better, however;

you can use this "chart" to figure out if the continuous servo would work as a drivetrain, the KG is how much weight it can handle on a axle (this is lifting force, but it would give you a good idea on weight limits)

on a x cm pole...

1cm - 6.5 KG, or about 14 pounds (this would be pushing it)

10cm - .65 KG or about 1.5 pounds

100cm - .065 KG or about .14 pounds

now, remember this is not factoring in the weight of the robot itself weighing it down or the surface it's moving on. i would think adding basic sensors and maybe a few little extras wouldn't hurt performance too bad, however.

Ok, thanks that will be a big help, I'll just factor in the weight of the robot when calculating for the leg servos. I'd use a standard drive motor, but I've no idea how to splice that into the EZ kit

I'm sure if you asked someone on the forums with a better knowledge of the motor controllers they could help you

also - i wouldn't exceed about 5-6 pounds even if the wheel was connected directly to the servo or you would have a very slow and probably problem prone R2

@xaviorbot.... Most people around here use a standard H bridge found here in the ez robot store.... There is even a great tutorial by a member on here (@Rich) and there is other info in the Learn section on how to setup and use it.... Cost is a huge plus, however I prefer ease of use. An H Bridge is a little daunting at first to get wired up and working. I personally prefer the Sabertooth 2 x 5 or 2 x 12 motorcontroller. Albeit way more expensive, it's a snap to use (just 2 wire hookup to the ezb) and to control it you send simple serial commands... There should be an example here (somewhere) on how to use the sabertooth as well.... Also, you can go to Dimension Engineering's web site to find out more about the sabertooth....

:)

Welcome!

You can use a modified HD servo and have servo City do it for you. They may not run as quick as you need though. Here's one that may work for you but you will need to choose your own. I'd stay with the quarter or giant size about servo. They run about 60 USD and 10 extra for them to change it to continuous rotation:

HS-805MG

You can then use the Modified control in ARC to control your drive train.

With that said I agree with these guys. A DC motor and H bridge is the way to go for heavier bots. Sabertooth is near indestructible and comes in versions that will handle up to 60 amps. With any motor controller choose one that will handle the amps your motor will be pulling through it. ARC has built in support for the Sabertooth so it's easy to control.

The Robot Market place has lots of motors to choose from. Windshield wiper motors are good for robot building. They have right angle, worm gear drive, are powerful and small. Down side is they pill lots of power and will drain you battery fast. Sabertooth has regenerative function to help with this when in use. a worm gear motor hold it's potion so it's almost impossible to move with out power. Also Look into the AME section first:

AME Motors

If your starting to build robots your going to have to learn how to wire up this stuff and understand a little about electricity (voltage and amps). It's good to know how to test voltage and what your looking for. Unless you buy a kit like the Revolution robots you'll have to wire up your own controllers, sensors and power supply without blowing everything up. Get a voltage tester and learn how to use it if you don't already.

If you have any questions just ask. There always seems to be someone here with the right answers willing to help.