I’m new to Blender, and while I have gotten a hang of making simple meshes, rigging is still generally eluding me. I’m trying to make a delta robot similar to what is used for pick and place machines. I have already made the model and added all the bones I think I need, but I can’t get the parenting and inverse kinematics correct so that moving the base of the robot moves all three arms without doing anything weird to the joints.
My biggest issue right now (I think) is that the foot of the robot has one bone that connects to three bones for the arms. I don’t know how to set up the links here so that I can get the inverse kinematics correct. Whenever I set the arm bones to have the foot as a target, the arm joints pop out of each other. However, I can’t set the foot bone to have the three arm bones as its parents and set the inverse kinematics from there, as far as I know.
Does anyone have pointers on some good tutorials I should check out? I’ve watched several, but the creators were using different versions of Blender and tended to implement things in different ways, so I don’t have anything really unified. I’ll try to post my .blend file here, but since I’m new I don’t know if I’ll be able to: http://www.pasteall.org/blend/29185
Thanks in advance
Is this what you are trying to create?
If so you need to create the arms as it is in rest position shown. Don’t have it straighten out like you have. Bone link will lock.
Yes this is pretty much what I’m going for. The issue with having it start in that kind of bent position is that I need to be able to flip which direction the knee/elbow type things bend. Wouldn’t starting it like that basically force them to move outwards always?
Looking at the .blend file, it needs bone roll set to orientate the bones correctly (make the axes visible on the armature so you can see), and IK should have pole targets to keep the elbow bends correctly orientated. Also seems IK for the legs should target the ankle and not the foot given the rig setup and it might not be an bad idea to set IK locks and stiffness under bone settings.
Other than that, nothing too bad that I can tell. Somebody more experienced at rigging might have some better pointers.
What I ended up doing was creating a bone in the center of the foot with three child bones that ended right at the ankles. I set the IK targets for each ankle at the corresponding child bone. This seems to work as long as I don’t move out of the plane too much. The foot stays attached if I try to set it too low, but it still slightly detaches itself if I try to pull it too far in the xy plane. It’s good enough for my current purposes. As I work on it I’ll look into incorporating some of your suggestions.
Device like this you really need to understand how links are setup. Also geometry of the device itself must be carefully followed. Once you understand how it works, you can experiment with different geometry.
Functionally, as far as I can see, the three main drive arm rotate up and down on single axis. At the end of drive arm is the T bracket that supports two links at each end with ball joints. And finally the links are attached to the end effector platform plate at the same spacing as T bracket with ball joints as well. The links, T bracket,and the effector plate forms rectangular shape. Those link arrangement forms a parallelogram. So, if you hold T bracket horizontal at all times the platform underneath will stay horizontal as well. Platform plate will not tilt at all when different arm is raised or lowered.
This means arm rig needs to be allowed to rotate in one axis only. Two other axis need to be locked. And you will need two link bones for each arm. I put the Empty objects as a target for each link and made end effector plate as a parent of all the Emptys to make it work:
For some reason I couldn’t log in for a few days to mark this as solved (the redirect page kept logging me out, weird). Anyway, thanks for all the help, I’ve got everything set up the way I want it now.