Handle multiple sprites as one body

[Davaaron]

Hi,

 

I got a complex object which is built dynamically and consists of multiple parts using box2d. By using joints, I keep them together. That complex object behaves like a single object now (although collision is another topic, as the object behaves really strange). The problem is, that box2d doesn't listen to assignments for velocity and messes up my physical behaviour like jumping and turning. 
 

I wanna remove all joints that I have until now and wanna make my own solution to handle the object parts as one object. How should I do that the best way?