Thanks for the quick reply Chris!
Here's what I've got so far, I haven't moved on with it, since I keep running into this problem. I can attach the hinge to the platform, I then group the two wheels with the hinge. I can then attach the two ball joints to the wheels...then my problem starts. When I try to get the two "poles" attached to the ball joints, the wheels and hinge become unglued from the platform. No approach I've attempted has yet to work. Greatly appreciate the help on this!