# Specific 3D Printing Applications / Fields / Conferences > 3D Printing in Robotics >  Inmoov Jr Robot Project

## Geoff

Hiya!

Some time back I consulted the maker of the Inmoov Robot Hairygael and asked him if it was feasible to make a smaller version of his robot, he said the servo's for the shoulders and things might be an issue as they wouldnt be powerful enough, but sure it might be possible..

Well, that was good enough for me  :Smile:  I figured the smaller frame means a lighter load, which means less torque required for the servos, and luckily it's worked out so far. I started about trying to find the perfect scale for the inmoov that both my printer could print and I was comfortable working with electronics wise and hooking and threading all the tendons etc.  I made one of the ?Inmoov finger starter kits, which is just one finger and a servo, which gives you a good idea of how to build the fingers and what to do and what not to.. how loose, tight... servo centering etc... it's a good starter.

Anyway, cut a long story short, many test prints later, I managed to pump out the hand and forearm and they work really well, once this demo program is finished i'll post a video. 

Why do a smaller one? It's cheaper basically  :Smile:  The servos are cheap, the parts are faster to print - so once the scale is set you just stick to that rule, which in my case is 64%. 

All the parts are scaled down to 64% - thats it. I did need to model some new servo horn-pulleys because there just was no fitting the other ones even after rescaling, but other than that - this is not a hard one to do, it's just time consuming threading all the fingers and getting the tension right.

I will keep updating this thread with the progress of it. I am not really keen on the design of the Inmoov Head, so I think I might see about making something else for the head neck and torso, but the hand design he made is fantastic.

photo 4 (4).jpgphoto 2 (7).jpgjr1.jpgmetal.JPG

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## Geoff

Ok well a week into making the software and many tests... We had a break!  :Frown: 

It seems fishing line and super glue really is not a great combination (to stop the slipping of the line when the servo's move...)

Anyway... long story short... I have decided to dissasemble the arm, I am replacing the servos with MG90s servos all metal geared (not these cheapo blue 8g plastic ones, they shred pretty quick and overheat under stress) 

I am also replacing the fishing line with some 1mm wire rope, if anything the fingers will break before this stuff does.

This is the rough GUI of the program im writing to interact with the hand in a fun way

I just found a nice source code for sending strings to the serial port, thats it really. You load the Arduino program to receive, when it gets a command like "grasp" it will then obviously use that sub to grasp the hand, all pretty basic.
Have to add the buttons now really, not much.. a little bit of work. Got sick last week and also started a new job, so time has been a bit tight for anything. 

ddsc.jpg

The VS code looks like this pretty much, there isnt much to it..



> Imports System.IO
> Imports System.IO.Ports
> Imports System.Threading
> 
> Public Class Form1
> 
>     Shared _continue As Boolean
>     Shared _serialPort As SerialPort
> 
> ...


And on the Arduino side, you just upload this (it's incomplete, I figured everything out, got it working and then left it at the thumb, but this is a complete example, easy to modify and update)




> #include <Servo.h> 
> 
> //Assign Servo's (could be done in an array if you prefer)  
> Servo thumb;  
> Servo indexf;  
> Servo middlef;  
> Servo ringf;   
> Servo pinkyf;  
> 
> ...



But probably the best thing that happened today.. my servo shipment arrived muwahahahahha.... I can now start constructing the new torso and head/neck/spine.

ddddc.jpg

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## Geoff

Well, after much hair pulling and teeth grinding... I found the perfect material for the tendons. 1mm Wire rope, too stiff. ... Brass braided wire... too bendy..

But, 80 pound fishing braid, now that is some strong stuff. When doubled up it is virtually unbreakable, certainly more than servos will do (that's 60 kilograms of tension these can take)  so I have rewired the junior hand, and in the meantime decided to make another full size arm. The full size arm took hours... the arm pieces I printed very fast so I got some banding and this was printed on 3 printers, so the prints do look a little off as I was pushing them all to their max. 

The grey small hand is all ABS, I went with all PLA for the large hand, and I have to say I prefer ABS... it sands much better and overall a much stronger material to work with (PLA gets hot and goopy when you sand it too fast)  But the PLA allows for pretty damn fast printing, for me I can print in PLA much much faster if I crank it to print at 210c.Anyway, here is a pic of the new big hand using the new fishing braid and 6 x MG996R servos.

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