Sunday, August 22, 2010
Getting to grips with the telepresence finger design
Having worked my way through a number of bugs in the Slice and Dice software I managed to get a workable design for the takeup reel of the telepresence hand finger/hand segment assembly. Space constraints reduced the reel diameter to 6 mm.
Last night I did a quick lashup to test the assembly.
I hadn't worked out what effect that small diameter reel would have on the force levels that the gearmotor. When the gearmotor pulled the unglued assembly apart I began to get an inkling of the implications of my design constraints. Doing after-the-fact calculations I discovered that the gearmotor was applying a maximum of about 4.75 kg to the finger tendons. That is an almost crushing force.
This feedback had immediate effect on a number of design decisions I had previously taken. I had been using nylon twine for the tendons. That was not so much a problem save that I had undertaken to use a simple knot in the twine for securing the tendon to the reel. It seems fairly clear that that isn't going to work.
I'm currently thinking that lead or steel crimp beads of the sort used in sash cords for venetian blinds may be more appropriate.