Upgrayd's AX Darwin Project

[Upgrayd offline]

Hey everyone,

I wanted to share the progress I have been making on my AX12 Biped project based on the DARwIn-OP project.

The mechanics of my biped are all custom design and fabricated by me to mimic the joint configuration for the DARwIn-OP.

The main controller for this robot will be a Gumstix Overo COM booted from a micro sd card with and an image of Linux version 2.6.36 and the GNOME desktop. This image also includes native development tools for c, c++ and python.

The software controlling this robot is all custom but heavily based off of the open source code released from the DARwIn-OP sourceforge page.


Overall Picture. From foot the shoulder the robot stands a hair over 1foot tall.


Close up of the feet.

Here are a two videos of the robots fist steps:

http://www.youtube.com/watch?v=tFE8Lseg6IY
Forward walking.

http://www.youtube.com/watch?v=D8nuekcSKko
Sidestepping and turning in place.

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http://upgraydlabs.com/
http://upgrayd.blogspot.com/

[i-Bot offline]

That's looking really good.

Are the side steps and turns based on IK and a gait ?
Did you include these into the walking module, or add a new module.

Are the 5 AX12 in the torso mounted direct onto the backplate ?

[Upgrayd offline]

That's looking really good.

Are the side steps and turns based on IK and a gait ?
Did you include these into the walking module, or add a new module.

Are the 5 AX12 in the torso mounted direct onto the backplate ?

The sidestepping and turning are both part of the walking module all using the same gait and kinematics engine.

The torso servos are all mounted directly to the backplate. The backplate in the images and video is temporary until I can get the material make the aluminum equivalent.

[nunogato]

Hi Upgrayd,

First of all nice post and project

You mention that you have custom design and fabricated some parts to mimic the joint configuration of the DARwIn-OP but I see a big difference.

The knee servo on the DARwIn is connected with the upper leg, check this photos

100_2038 by RoboSavvy, on Flickr

100_2033 by RoboSavvy, on Flickr

100_2041 by RoboSavvy, on Flickr

If you need any extra info about the DARwIn let us know

[Upgrayd offline]

Yup, The knee position is different.

I had to change the knee mounting in order to keep the robot as short as possible.

The end result is the same joint to joint proportions as the darwin.

[i-Bot offline]

As Upgrayd says the difference is minor. The overall joint layout is the same since it is only the axis which is important not the servo position.

If you conform to the general Darwin OP joint layout described here:
http://robosavvy.com/site/index.php?opt ... 1&Itemid=2
then changes to the software are parametric changes for the different dimensions and some setting of servo directions and zeros.

If you diverge from the Darwin-OP layout, then more work is required to modify the IK code.

The other thing is joint constraints, though that is more important form complex moves like getting up, rather than walking.

[Tyberius offline]

The other thing is joint constraints, though that is more important form complex moves like getting up, rather than walking.

Just to confirm, this is actually set via CCW & CW angle limits in the registers of the dynamixels, correct? I noticed that the dynamixel firmware upgrade script sets this for each ID.

[i-Bot offline]

As you diverge from the standard DARwIn OP build then the physical joint angle constraints will change. the first stage is to measure the actual joint constraints of your configuration. Some allowance needs to be made for protection and consideration for how the legs interact. The objective here is to set CW and CCW limits to give best servo protection.

While the MX firmware installer has hardcoded limits which are set with firmware updates, this may not work for AX based robots. The dxl_monitor also sets the CW and CCW limits on RESET. Again these are hardcoded and must be changed to meet your configuration above.

There may also be value to adding some debug code to the action or walking modules to flag if limits are ever exceeded in custom configurations.

[MOHIT JINDAL offline]

Hi Upgrayd,
I saw your blog. Can you tell me from where you got aluminium frames ?

[Upgrayd offline]

Hi Upgrayd,
I saw your blog. Can you tell me from where you got aluminium frames ?

I designed the brackets in a 2D cad program, had them cut by a waterjet service and bent them on a metal brake.