Hi Professor, First, I apologize for posting again. We have been working very hard on our model, and unfortunately have not been able to get it to work. Based on your last responses, I believe you may be misinterpreting the model (or perhaps we are completely misunderstanding your suggestions): "From your picture though, it looks like the strings/tendons are passive elements while the solid rods have actuators in the middle. If so, you could model each rod as a pair of capsules with a sliding joint between them, and actuate the joint." and "If there is an actuator at the end of each rod, that means each rod is a pair of rigid bodies sliding relative to each other. So each rod should be modeled as a free body that has one child body, with a sliding joint between the parent and the child. That joint should be actuated (instead of actuating the tendons as you are currently doing)." In fact, the strings are not passive. Each strings contracts (its end coils around an actuator) in order to pull two rod-ends closer to each other. Each rod is one single rigid component with fixed length (not two rods sliding relative to each other, as parent and child). To make this more clear, please see the video below (beginning at 00:20): Notice that while in the real robot, the actuator contracting/pulling the string is in the center of the rod, it is equivalent to place this actuator at the tip of the rod, and contract the string from that point. Would you be willing to help us model one rod, with its four attached tendons, joints, etc... ? We would truly appreciate it. We are also happy to get on a quick call (only if that would be easier for you than answering our likely confusing posts). Either way, we truly appreciate your help, and are very excited about the possibilities for this model, once it is completed and realistic. Thank you again! Best,