Help with robot driveline design

[sbonkosk]

Im currently working on a project for a lawn mower robot and need some help with motor selection and mounting of the motors.

We're not sure to go about using 2 motors out back and a free moving wheel up front, or 4 wheel drive. We estimate the robot to be about ~20 lbs or less, and our goal is 1 foot/second speed.

We have no experience building a mechanical system like this so we messed up the first time around. We built a frame, mounted the motor to the frame, and then the hub to the motor shaft which connected to the wheel. That was it. This ran for a little bit but then 2 of the motors seized because of the weight being supported by only the motor shaft.

So we're trying to figure a new approach to actually mounting the wheels/motors so that the weight won't destroy the motors, and also looking into possibly new motors because we're returning the 2 that are currently still working.

These were our original 4 motors

http://www.robotmarketplace.com/products/0-B231.html

We're thinking of now getting 4 of these instead

http://www.pololu.com/catalog/product/1107

Can somebody recommend a better motor choice for our application? 12v, 1ft/second speed, going through grass, robot weight ~20 lbs or less, low cost.

Should we go with a 2 wheel or 4 wheel design? Would either be fine?

Also, we're now thinking of mounting the motors like so:

http://yfrog.com/f/evimag0386aj/

Will this avoid the weight of the robot being forced on the motor shaft?

 

[Navin A S]

Are there any other considerations we should be aware of when mounting the motors?Thanks for your help!