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Mini ROFI

by jdow, published

Mini ROFI by jdow Nov 26, 2012

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Summary

This is a 1/3 scale model of the bipedal robot ROFI (http://www.thingiverse.com/thing:32048). It has all of the same parts as ROFI, but the electronics and servos are all printed (i.e. the robot isn't going to be moving by itself without a lot of imagination ;-). I originally created it because I just got a Replicator 2 and wanted to see what the new printer was capable of. After the model was printed and sitting on my desk two things occurred to me :

  1. Working at 1/3 scale would be really useful for prototyping future robots.

  2. Because it was so fast and cheap (3 hours to print and $2 in parts) it might be a good "gateway drug" to get more people to try building robots. After all, I never really thought I could build robots until I downloaded the parts and built a modified Z stage for my Cupcake printer.

Instructions

These parts will only be printable on 3D printers that can do really fine detail (such as the Replicator 2). I used a TOM to print the full sized ROFI, but my TOM could have never come close to printing the mini version. This is an open invitation to prove me wrong ;-)

I would suggest printing the electronics and servos in black plastic and the other parts in your favorite color (the mini in the picture is clear PLA).

Non 3D printed parts :
4 mm socket head M3 screw x 16 (part# 91290A109)
8 mm socket head M3 screw x 7 (part# 91290A113)
20 mm socket head M3 screw x 12 (part# 91290A123)
led
led holder (could also print this)

The part numbers are from http://www.mcmaster.com

Follow the building instructions for ROFI :
http://www.projectbiped.com/prototypes/rofi/instructions
but skip the servo preparation and calibration steps.

The differences with the full sized ROFI instructions are :

The 4mm screws are for the body.

The 20mm screws are for the joints.

The 8mm screws are for the heels, body riser to center bracket/bearing frame connections, and holding the electronics together. When screwing the electronics together (the Android tablet, Arduino Mega, and USB host shield), make sure to leave a 2mm gap between the Android tablet and the Android Mega so that the Android tablet still slides into the top body panel properly.

The front, right, left, and top body panels are combined into a single part to make the final result stronger.

The heels screw into the batteries in the feet (instead of screwing into the feet directly).

Instead of a power switch in the right body panel I used a led with an led holder (had one laying around and it looked cool). Feel free to print the led holder if you don't have one (or print the led for that matter).

I also used a metalic silver shapie marker to make the back of the Arduino Mega and the front of the ultrasonic range sensor look more like metal.

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Wow very cool, maybe use micro servos. Seeing you do it 1st assures me that I too can make small lightweight robots!

jdow - in reply to Nigete

 I had the same thought ... I found some 1.7 gram servos that are very close to the correct servo size (just about 30% taller).

http://www.hobbyking.com/hobbyking/store/__17540__HK_5320_Ultra_Micro_Digital_Servo_1_7g_0_05sec_0_075kg.htmlhttp://www.hobbyking.com/hobby...

They are pretty flimsy though, I've already killed 2 of them (ordered 15 to have a few extra).  The connectors are crazy small and I haven't been able to find a place to buy the female version.  I might just end up soldering the wires directly to the board.

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