Prodos - Bipedal Robot

by jdow, published

Prodos - Bipedal Robot by jdow Aug 6, 2011

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Prodos is the second prototype robot from Project Biped (www.projectbiped.com) whose goal is to create an open source 3D printed dynamically balancing walking robot. Prodos was designed to demonstrate how to coordinate simple limb chain actuation using a microcontroller. It has 8 degrees of freedom (joints) and can perform a simple walking action. The servos used were selected for economy and aren't powerful enough to bear the robot's own weight, so Prodos must be externally supported while it is executing its walking action. See a video of Prodos in action at www.projectbiped.com/prototypes/prodos/walking-analysis

Prodos has the following features:
Uses an Arduino Duemilanove microcontroller
User interface via OLED display and 4 button panel
8 degrees of freedom
Detailed assembly instructions


A full overview (with source Blender files) can be found at the Project Biped Prodos website:

printed part diagrams:

non-printed parts manifest:

assembly instructions:

programming instructions:

operating instructions:

walking info:

more pictures of the actual robot:

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What is my purpose?

What size servos is this designed to use? "regular" size, or 9g? I know there are more, but those seem the most common. Though I'm not that familiar with the different types..

It uses 7g servos. See the link for the parts manifest in the instructions for details. Be advised that the servos aren't strong enough to actuate the robot under normal conditions (you'll have to pick it up to see it move). If you want to make a robot that can walk search for FOBO or ROFI.

You might try springs as a way to unload the servos. I've had good success using tension springs to allow a 2 DOF quad to walk with weak servos.

That sounds interesting. Are there any resources on using tension springs you'd recommend?

Not that I can think of. I just fiddled till I got it basically balanced when in a neutral position. This means of course that now the servos will have to push to get it to squat as well as to extend, but either stance should require less (half in an ideal world) torque than an unassisted stance. A leaf type spring, (flat strip of spring steel) might be even better for your bot. Might be harder to find the right spring of that type though whereas tension and compression springs are a common hardware store item. Or rubber bands, or those plastic elastic bands they make for girls hair.

Or mouse trap springs, ... :) Pretty much anything that will supply some torque to counteract the torque due to gravity.

I like that first picture, it looks like Prodos has arms and he's raising them for joy :P

I call that the T-Rex step ;-)

Thanks! I think your CUBE record for using the most plastic on a single project is safe ... at least for a few more prototypes ;-)

Might want to look at the Lynxmotion Biped Scout: http://www.lynxmotion.com/c-67-scout.aspxhttp://www.lynxmotion.com/c-67... I always their SES (Servo Erector Set) could be efficiently 3D printed instead of made from aluminum.

Would love to see it really walk with something like HSR-5590TGs.

That's a cool robot ... and at under $200 it is a good value. Based on the close up pictures, it doesn't look like there is any positional feedback from the servos. A single one of these servos you mentioned (HSR-5590TGs) is almost more than the robot! Maybe too expensive for a hobby project? For the next prototype I've been looking at the T-Pro MG996R 55G


which has some nice specs for a $12 servo. Do you have any suggestions for a good servo in the under $20 range?

This is very cool! Will its successor have jump jets and rocket launchers? ;)

Maybe a few generations down the line ;-) I guess it could be combined with the quad-copter design I saw posted on Thingiverse to make it fly...

so how will you attach stronger motors?

The next prototype will be a bit larger to accommodate beefier servos. I've been experimenting with 55g servos


and been pretty happy with the results so far. I've also redesigned the joints to avoid having to use the radial ball bearings.

This is an awesome project! What would be really awesome is modding the brackets for use with Dynamixel AX-12A or AX-18A actuators. With the ability to create movements by just positioning the actuators it would bring another level of ease to the process.

The Dynamixel actuators have a lot of really nice properties ... I especially love the daisy chaining, rotational feedback, and the torque. I had looked at using them for the next prototype, but thought (perhaps foolishly) that I'd try and come up with a positioning solution for a cheaper servo. The next version will need to have 6 DOF per leg (for static balancing) which would add up really quickly if each servo was $45 or $95 ;-) I've been experimenting with radial potentiometers for feedback and have had promising results so far.