InMoov Finger Starter

Now that I got the calibrator working (at least for the time being) I have moved on to the actual Finger tutorial. I did have a bit of surface adhesion problems while printing but once that was resolved the steps were easy enough to follow.

There are a few things that are worth mentioning.

The tutorial uses metric drill bits to re-drill the holes int he printed parts. Unfortunately I did not have the exac ones, so I had to use approximate replacements:

3mm  -- may need to use a 1/8" (3.2mm)
3.5mm -- may need to use 9/64" (3.6mm)
1.5mm -- may need to use 1/16" (1.6mm)

The instructions also suggest using 3mm filament pieces on the joints but I did not have any. I used M3 bolts instead with nuts to secure them because my slightly larger drill bits had left the holes a bit too large. Since this is just a prctice finger I think it's OK for now, but I'll have to revisit this issue or at least cut the excess off the bolt length.

Even a single servo will probably need more power than what the Arduino board can provide. Be sure to use a battery or other power source. I could not find any specific details on how much current the recommended HK15298B can draw but the best clue that I found online suggests it can be around 2 A, which is a LOT. An average AA battery (don't quote me on this) can provide only about 50mA so instead I found an old power adapter, cut the tip and used it to power the servo.

Once I programmed the Arduino with the provided script, another little speedbump I ran into is that upon the first try the servo did not move. The trick to solve that was to make sure that the power adapter I used and the Arduino shared the same ground. In my particular case I was using USB to power the board, so I just used a wire to connect the ground pin to the ground wire of the power adapter for the servo using a breadboard.

I also noticed that the servo can mechanically move 180 degrees but in reality it only moves 90 degrees. This is something that I overlooked when looking at the list of compatible servos from the InMoov website (It's clearly stated there) and I wasted like an hour trying to figure out why the board did not turn it all the way. My bad.

In the end it all worked out, although I still need to think about the buzzing noise made by the servo when it's at the max position pulling the finger. It makes the same noise even if there's no load, so I suspect it may be related to the low(ish) voltage fro my power adapter, maybe it will work better once I provide at least 6V.

InMoov Calibrator

I have decided to start the journey of building the famous InMoov robot. I have started with the basic Finger Starter and the very first thing to do is calibrate the printer to ensure that the parts will fit together properly.

I am using an Ender 3 printer, Cura and PETG filament. Upon my first attempt the pieces were so tight that once I was able to forcefully put them together I could not pull them apart.

Calibrator with 0.0mm horizontal expansion

After a bit of searching, I found that others with the same issue had been able to fixing by changing the Horizontal Expansion setting in Cura. They suggested different values, so I had to try for myself. That setting affects the "holes" in the print, negative values means the holes are more "loose". I tried -0.2, -0.4, -0.1, -0.05 and -0.08 mm in that order. Here's some pictures with the results.

Calibrator with -0.2mm horizontal expansion

Printing with -0.2mm left the pieces fit but a little too loose. Then I still went on to try -0.4mm to see how much different it was and the result was as follows.

Calibrator with -0.4mm horizontal expansion

This time the holes were even bigger, by too much. So I moved the other way and tried -0.1mm.

Calibrator with -0.1mm horizontal expansion

That one fit almost perfectly but I still ha dto try to get better results, so I went for -0.05mm.

Calibrator with -0.05mm horizontal expansion

This time the sides fit tight but not too much, the problem was the center rectangle that I could not take apart after trying for a few minutes. So I finally tried -0.08mm...

Calibrator with -0.08mm horizontal expansion

And here I stopped trying! It fit slightly better than -0.1mm and I could remove the pieces easily.

Conclusion: If you are having trouble with the calibrator pieces not fitting, I'd try the Horizontal Expansion setting on your slicer first, your perfect number will be most likely different than mine but somewhere between -0.1mm and -0.2mm is a good place to start.