[Zabco]

The two programs are pretty much the same. I've still got a copy of Cubify Design (from when 3DSytems owned the software) and it works the same way. I played around some today with the 'flexible' function. It does work but is somewhat persnickety about how you set up the assembly. I drew up a basic engine using 3 cylinders with wrist pins and connecting rods. A piston with connecting rod and wrist pin was created as one assembly. A crankshaft with 3 - 120 degree connecting shafts as a part, and a basic engine block as the third component. Started a new assembly by bringing in the crank and constraining it to the Z axis and centered on 0,0. Then imported three copies of the piston assembly. First I connected each piston without enabling flexible to the crankshaft with a vertical constraint. As expected, the assembly locked up with the second piston and would not rotate. Next I enabled flexibility. Connected first piston assembly to crankshaft and constrained to vertical position directly over center of crank. Piston would move up and down with crank rotation. Added second piston same way and crank would rotate. Thought that this was going to work ok. Added third piston and the assembly locked up and would no longer rotate. All three pistons were in alignment and connecting rods were free to swing back and forth. Happened to glance at left hand column and noticed I had a number of constraints shown in red meaning they were bad.

Thought about what was going on and came to realization that I was over constraining the piston assemblies. What I forgot is that they already had some constraints carrying over from their original construction. Adding the three additional constraints placed on them in the new assembly and they froze. Deleted the piston assemblies and all their related constraints. Imported the engine block and centered it in X and Y over the crankshaft and anchored it in place. The engine block would serve to align each piston directly over the crank, properly space each piston along the crank and serve as the vertical guide for the pistons. Add each piston assembly back, enabled flexible, put concentric constraint between each piston and cylinder bore and a concentric constraint between crank and connecting rod. That's all, no other constraints. Added other two piston assemblies in same manner. "Grabbed" the crank and gave it a twist and it spun with all pistons going up and down as the should. So the 'flexible' function does work but you just have to be very careful in how additional constraints are applied. And, I think, not constrain part that will move to planes or axis.