Question: How do I connect 3 arms to a single part with revolute joints?

I have created a model for a robot in Solidworks and have imported it into Maplesim using the CAD toolbox. The problem I have is that the robot has 3 arms that are supposed to come together on a central piece pictured below in figure 1, but attempting to simulate the model with all arms connected with a revolute joint as in figure 2 yields an error that says "The system is underdetermined" the location of the error is main.

For the purposes of the image below I only connected one of the arms, this allows Maplesim to run the file successfully.

figure 1 showing the central piece that the 3 arms are supposed to connect to.

Figure 2 showing the problem revolute joints circled in black, the error at the bottom and the setting of the revolute joint on the right.

Essentially my question is how do I get the model to work? I apologise if this problem is not terribly well demonstrated, this is my first post onto this forum so I am not sure of all the standards.