Monday, February 11, 2013

Left arm of Inmoov robot complete

Printing an assembly for the left torso, shoulder, bicep, forearm, wrist and hand is complete.

Front view of left torso assembly, shoulder, bicep and base of forearm.

Detail of rear view of upper torso and shoulder.

Left arm raised.

Forearm flexed.

Forearm extended.

Detail of lead screw and collar controlling the left shoulder.

The Hitech HS-805BB servos that drive the torso and arm kinematics are on order.


  1. Great, great work Forrest, Love to see this. One question, you mentionned on your devative Thingiverse, printing your parts with a 100% infill. It wasn't what I recommended though. AhAhAh, Did you print all parts like this? If yes could you weight it, or some parts to give me an idea. This will be important once everything is mounted together with servos.

  2. I didn't say what I meant. I printed the parts in the setting next to 100%, not right at 100%. From the looks of some of the failed prints that setting is about 60%-70% fill, I would guess. The parts seems sturdy enough.

    It should be easy enough to figure what solid parts would weigh, though. Just open them in Netfabb and multiply the volume by 1.04 to get the number of grams for the part.

    1. Oh good. I was a bit worried for the results. Any extra weight on you built, is weight your robot won't be able to lift up. Calculating all the parts is a long task... Thanks for the tip.

  3. I am not so much worried about weight at this point. I did this print to get acquainted with how the parts went together. I just ordered some more filament, so if I have to reprint everything later on, it will not be a serious matter.

    One thing puzzles me, however. The contoured set of four pieces that make up the structure of the forearm. How do those hold together? So far I've used tape, but I can not yet see how the assembly works in final form. I am sure you talked about it somewhere in your blog, but I haven't run across that yet. :-)

    1. I the "assembly sketch", picture 5 and 6. What i did was gluing with acetone the parts.
      Looking in
      has the instructions steps which should tell you what to glue with what.
      I never did a step by step for the forarm because it was the beginning of InMoov.

    2. Glue with acetone robpart1 to robpart2v2 and robpart5V2 together. This will be the base of the forarm. Make sure the servo brakets are aligned.
      Glue together robpart3 and robpart4V2, this will be the cover of the forarm
      Make sure the servo brakets are aligned.

  4. "Any extra weight on you built, is weight your robot won't be able to lift up."

    Couldn't we just change the gear ratios in the worm gear assemblies? That would lower our movement speed, but we should be able to get more torque.

    As well, if we redesigned the worm gear boxes using cheap 608 bearings {the kind used in skateboards}, we ought to be able to recover a lot of the energy we are losing to friction inside the gear trains. :-)

    1. We could change the gear ratio, but my first print had a gear with more teeth,I don't remember how many, I need to look in the junk box. Anyway it was going too slow, a slow robot is quite boring, I think. At this point it is better to get a more higher torque servo.
      Of course bearings would be much better, but I designed it to be as less expensive and the most easy to gather parts. Many people already freak when they see servos, so if I would add, bearings, screw leads and special bolts, there would be even less people ready to try building it.
      Improvements like you propose are great, because the more high tech builders will have the option to choose.

    2. "Of course bearings would be much better, but I designed it to be as less expensive and the most easy to gather parts."

      Ordinary bearings are indeed expensive, but 608 skateboard bearings, which have a 22 mm outside diameter and a 8 mm inside diameter, cost about $1 each. We used them a lot on the open source 3D printer Reprap project simply because they were so cheap. I am not sure about Europe, but in the United States you can get them in any sports equipment store in rolls of eight. :-)

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