Older blog entries for RobotsAustralia (starting at number 4)

Options for AX-12 Robot Legs

While I wait for the Dynamixel Robot Controller PCB to arrive from the board manufacturers (update: they got here this morning! looks great!) I have returned to the mechanical design of the Quadruped4 robot.

I was never really happy with the look and function of the leg and hip design I have to date for the little creature, and thought I would create some alternate concept simplified cad models to look at other possibilities.

This is how I last left the mechanical design of the legs. The two axis shoulder or hip joint is implemented by two Dynamixel hinge brackets end to end bolted, at ninety degrees to each other. The thigh is made up of the two AX-12 servos end on to each other.

My main complaint about this configuration is the distance between the two axis making up the shoulder, which tends to make the upper part of the leg look out of proportion if it is fully extended downwards.

Alternate Concept 1
The first thought was to perhaps mount the forward swing servo onto the horn of the other hip servo, this allows really good thigh range of movement, but the bushes in the servo probably won't like all the load on the horn. Better to use the passive hinge point on the other side of the servo as well with one of hinge brackets.

Alternate Concept 2
Robotis manufacture an offset hinge bracket which I thought might be more useful than the straight bracket in allowing a greater range of motion of the joints given horizontal mounting of the thigh servo (as shown left). The image shows crouch and full reach (both dimmed) with standard stance pose undimmed.

Alternate Concept 3
I turned the offset hinge joint around on the thigh to hip joint to see if that improves the range of motion. I don't think it does (see the dimmed forward reach motion in the picture to the left) as the limb can't reach forward particularly far. The crouch pose does look a bit more 'natural' I suppose.

I can't say I am really satisfied with any of the options thus far; more cad experimentation required!

Syndicated 2007-05-24 01:04:00 (Updated 2007-05-24 04:08:56) from Robots Australia

Dynamixel Controller PCB design finished

I have been grabbing the occasional hour here and there and have finally finished the layout and routing of the Dynamixel Robotics Controller PCB. A little bit of clean up and it will be ready for submission to the board manufacturer. I have to get going on ordering the parts for it while the board is getting made.

On the web site front, I have put together some info for the page about the Quadruped4 design which uses the Dynamixel Robotics Controller. Hopefully it can help other experimenters find suppliers or gather useful information from the approach I have used.

Syndicated 2007-05-10 06:58:00 (Updated 2007-05-10 07:02:56) from Robots Australia

Web site progress; filling in information slowly...

I have been tackling the Earlier Work page, and have created a lot of content about the investigation into low pressure pneumatic cylinders from MUTR, and the evolution of the Quadruped4 design from its early beginnings as a big heavy cordless drill motor driven creature.

Syndicated 2007-04-30 07:31:00 (Updated 2007-04-30 07:35:36) from Robots Australia

RobotsAustralia Blog Created!

Robots Australia now has a blog!

Syndicated 2007-04-17 03:24:00 (Updated 2007-04-17 03:26:47) from Robots Australia

Hello everyone, This is my first blog entry on robots.net, but I have already been maintaining a blog at http://robotsaustralia.blogspot.com which mostly contains notes on my current robot Quadruped4. I will probably try to cut and paste blog entries here, or at least link to appropriate pages on my website http://robotsaustralia.googlepages.com .

Here is the most recent blog entry, before I took off on a month long holiday, so it's already a bit out of date!

Tuesday, June 12, 2007;

Time to post an update on what has moved forward with the Quadruped4 robot design. The PCB for the Dynamixel controller has arrived, and all parts for it as well, and also quite a bit of cad work has been done playing around with various options for the mechanical design of the robot.

Here is a photo of the PCB partly loaded. You can see the two Atmel Atmega micros, one is the AtMega128 and the other is the AtMega2560. On the far right is the outline where the WiPort WiFi module will go, with a few parts carefully fitting underneath it in just the right spots where there is some room.

I have also been working on the mechanical design of the robot, and although there is still much to do, and I am not fully happy with several areas, I think the robot will eventually come out something like the design pictured here. Note the WiFi antenna naturally positioned as a tail...

Earlier images I created for this robot didn't have the right cameras on it, whereas I have created a somewhat hasty model of the C328 serial camera modules I actually intend to use for this model. Also check out the shoulder joints for the legs, these use a custom bracket I have designed for the Dynamixel AX-12 servos which forms an offset hinge between two AX-12 servos. This function could be served by the Robotis offset hinge and flat plate bracket put together, however that would be bulkier and would not quite have the configuration I am after. The brackets form a left and right pair, and attach to each side of the AX-12. I will machine these out of nylon or similar material, and although the machining will be a bit tricky, I think I should be able to achieve it.

Here is another view of the design as it stands. I'm not sure of the top cover, it is really not needed, and I kind of like the idea of seeing the electronics etc, but it will offer some protection I suppose. I need to make plenty of asthetic improvements to the shape of some of these panels as well, the whole thing looks a little like a skateboard deck at the moment.

Anyway, this will be the last post for a month or so, as I am travelling to Italy for a holiday, so robot work will take a break too! When I return, I shouldn't expect it will take long before all the parts are loaded onto the controller and I can attempt the all important critical first turn on...

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