Older blog entries for Roko (starting at number 2)

First Assembly of all Four Legs

Leg Parts straight from waterjet sized

Parts from water jet cutting

I received the remaining water-jet cut parts from Big Blue Saw a couple of weeks ago, and have slowly been working on taking them from rough water-jet cut pieces, to parts that will actually fit into the robot. The water-jet cuts are fairly rough when looking for precision parts, which is why a lot of work goes into the rough parts in order to get things to piece together nicely. To be honest, though.. I wish I had a CNC mill/router that I could have used to precisely cut the parts myself.

Waterjet edges sized

Water Jet Edge Finish

This isn’t to say that water-jet cutting is bad, but it is what it is. You have to account for the fact that water-jet cut parts aren’t 100% perfect to minute tolerances. Some of the issues I have with these parts are that the water-jet seems to have cut at a bit of an angle, which causes tolerance issues requiring some filing work to make sure everything fits together nicely. That said, I’m still happy overall with the water-jet cutting, and would recommend it to anyone trying to make more complicated shapes or numerous parts. I wouldn’t have been able to make all of the more complicated/curvy cuts by hand as precisely and quick as the water-jet service does. Plus, the edge finish has a pretty cool rough effect (Although I will be smoothing it out for this particular robot)

Four Legs in progress

Four Legs!

After a lot of work machining the parts, I finally put togethor the frame of the robot with all four legs for the first time (minus the robot’s feet, which I haven’t gotten to yet). There’s still a lot of tweaking and some machining I have to do on these parts before they’re finished, and then there are a lot of small parts that I still have to make. It’s been around 5 months since I started this project, and things are really starting to come togethor, but I’m thinking it’ll still be another few months at least before the robot even moves, let alone moves in a fashion resembling autonomous walking. At least it’s finally starting to look like an actual quadrupedal walking robot.

Stepping the shaft from 4mm to 3mm sized

Stepping the Axles

I also turned the axles on the lathe recently. Eight of the axles are simply straight 3mm shafts, however the four hip/base axles are 4mm in the center, and 3mm on either end with a center groove to hold an e-ring which is used to keep the flat-flex cable in place, and out of the gears. I still need to put the axles on the mill in order to flatten them out to keep set screws in place, and to drive the potentiometers I am using for axle position sensing. I’ll post more on those in the future when I get to that stage of the build

One of the other things I still need to complete are the motor controllers, and the actual robot’s brain (likely a Gumstix Overo, but I would have to make my own carrier baord). I have tweaked and fixed small bugs in the design of h-bridge prototype I built in the fall, however I want to move the same circuit into a shape that will fit into the actual upper-leg side piece. Luckily that gives me more space to work with than the current itteration of the board (which will be used for controlling the inner four motors), so it should be a relatively easy task once I find the time.

Syndicated 2009-02-08 22:07:44 from Roko.ca

Mini Sumo Beginnings

As with many projects, a mini sumo has been several years in the making, and has undergone several design revisions without actually having time to begin construction. But, finally, I took a bit of a break from the quadruped to start work on a mini sumo robot in the past couple days.

Aluminum Wheel Stock sized

Start of a wheel

I had some round aluminum stock sitting around, and felt like playing around with the lathe. I got my trusty hack-saw out, cut off a chunk of aluminum, chucked it up on the lathe, and started spinning. Over the course of one evening, I came up with a basic wheel and hub assembly to go with the Maxon 17:1 gear motors I’ve had lying around for almost a year now, waiting for a sumo robot to be built around them. This is the same Maxon motor many people use, and I had to contend with the same issue, that the motor length itself is half the maximum width of a mini sumo robot (About 50mm). This called for making a hollow wheel that would slide over the motor.

I made a two piece assembly, with a hub that is attached to the motor with a set screw, and a wheel that is attached to the hub with several 2-56 screws.

Wheel Bore Action Shot sized

Boring in Action

Overall, the boring went well on the lathe, but was definately a learning experience. The process itself was tedious, starting with drilling out a center hole using drill bits of incremental sizes until I had a center hole large enough to fit the boring tool, then slowly boring out a 21mm depth, 0.1-0.2mm at a time, slowing down as I approached the desired tolerance.

The tool itself chatters easily if you’re not careful, but I managed to produce a mostly clean bore. I’ll have to experiment/research a bit more on the best chip rates for turning aluminum stock…

Making the inner hub itself was easy to do, simply turning down the outside of a piece of aluminum, then using a couple drill bits to center drill a hole to about 2.85mm, then using a reamer to finish the center hole at a nice, clean 3mm to fit the shaft. A 4-40 set screw fit nicely, though I did have to file down a fraction of a millimeter that was sticking out from the hub itself, as that part of the hub fit with close tolerance into the wheel itself.

Wheel Assembly Parts sized

Prototype Wheel Parts

Wheel Assembly Assembled sized

Prototype Wheel Assembly

Using a milling machine to precisely drill the holes that I would then use to tap and mount the actual wheel to the hub helped keep everything nice and accurate. Once finished, the wheel and hub aligned very well, and I had a completed wheel assembly.. Now to finish the other wheel, make a tire mold, mold the tires, mount the motors to a chassis, and make a brain for it all.. Hopefully I can have a basic robot ready in time for this year’s Robot Games.

Syndicated 2009-02-04 06:02:27 from Roko.ca

Upcoming 2009 IEEE Robot Games

The 2009 IEEE/WCRG Robot games have been announced for May 9th, 2009. I used to be an avid participant, but first school and then work travel got in the way and as such I’ve only managed to make it out once in the past few year.

This year, I’m hoping to have a mini-sumo ready in time, one that I’ve been designing in the back of my head for several months (years?) now. I’ve had some tiny Maxon motors sitting around that I bought a year ago with the hopes of finding time to start this robot, and today took a break from the quadruped to finally start machining the wheels. I’ll try and post details later.

Anyways, if you can make it out to Calgary for May 9th, it’s definatley worth checking out the Robot Games. If you have spare time, make a robot to compete! It doesn’t have to be perfect, it’s more fun building a robot than winning…

Syndicated 2009-02-03 06:32:18 from Roko.ca

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