Wednesday, April 02, 2008

Building a robot - Day 2

Okay... so everyone knows that I've just started my latest project in building a robot. If you missed my first post on what motivated me and my thoughts, see here.

Last night I began working on the mechanics of the drive mechanism. After hunting through all my scrap parts for gears and motors, I finally found a set of matching gears and matching motors. My initial thoughts were to have the motor drive the gear which is directly connected to the axle. In my first attempt, I found that the axle was just a little too thin to hold the gear. I attempted to glue the gear to the axle but found that the glue doesn't work too well with steel. After more searching, I found a axle that was slightly thicker, however, it was a little too thick for the gear. No problem, I just used a hammer and hammered it in.

Which bring me to last night, where I was attempting to mount the axle, gear and motor to the chassis. My initial thoughts were to drill a hole through he chassis wall for the axle and to mount the gear and motor behind the wall, with the wheel on the opposite end. Unfortunately, as I discovered later on, this would not work as the weight of the body would force the axle to bend into the chassis as there is only one thin point on the chassis supporting the axle. To combat this problem, I decided to try and create a extension to chassis so that there would be two points of support for the axle. The gear and the gear on the motor shaft would now be on the outside, sandwiched between the chassis panel and the extension panel, with the motor sticking through the chassis panel.

Unfortunately, for me, my fabrication skills are seriously lacking; After pondering the best material for the task at hand for over an hour, I decided the best way to go was to use a strip of thin steel (an old pc slot cover) bent into a square horse shoe that would be bolted to the chassis. To me, this was great as the steel would be relatively easy to work with (being thin) and the mounting is rather simple... or so I thought. I was to discover, late in the night, that whilst the steel was thin and relatively easy to bend, it would not be easy to make into the necessary shape as the space is rather tight and I lack the proper equipment to bend the steel correctly.

So here is where I decided to leave the project and retire for the night. After a good night's rest, a thought struck me; Rather than using the steel, why not use a thin plastic such as that found on Glad brand tupperware. The plastic is thin enough so that it'd be easy to cut and bend into the necessary shape and also it's tough enough not to break easily. I guess it does pay to have a great night's sleep.

Tuesday, April 01, 2008

Building a robot - Day 1

So I got into robotics... again, last night. All of this came about from discussion I had with some fellow coworkers about how their kids were studying robotics in school using the Lego Mindstorms kits. All of this discussion got me thinking and so I decided to "scratch the itch" and document my successes and failures on here.

Last night I began working on the actual mechanical aspects of the robot. I have decided to keep it simple and to attempt to only use parts that I have sitting around (I have a lot of parts!) or that I can get for free (ie. I don't want to spend any money on this if I can avoid it).

After about an hour of thinking I came up with the following design; The chassis is a small plastic container that used to be a DLT tape case driven by 2 motors, one for each side driving the rear wheels. Rather than using two front wheels, the plan is to use a single caster wheel mounted in front. This should allow the robot to rotate a full 360 degrees on the same spot.

The robot will be remote controlled from my PC. The actual details behind the link have yet to be thought through, however, I do have a few thoughts in mind such as WiFi or Bluetooth (using a old discarded Pentium SBC I have laying around or by hacking a old 2ch RC I have. I figured I could "cross that bridge" when I get to it. At worst, I'll implement autonomous control using a microcontroller that can have instructions downloaded to it via a serial cable.

Rather than driving the wheels directly I decided to go with a small gear box on each wheel to help with the drive. Here in lies my first problem; Finding the right gears to attach to the axle and motor. It seems that of all the gears that I have (and I have a LOT), none of them match! - They are all of different ratios. I guess I'm just going to have to work out a way to mash various different gears to from the same ratio on either side. My other hop is to be able to scrounge for parts at my family and friends place. If anyone out there has an old VCR, DVD player or cassette deck that they don't need, please let me know.

For now, until I can find the right gears I went ahead and began working on the main body by drilling holes for the axle bearings, etc. - I hope to have some pictures up once my wife brings home our digital camera.