Thursday, 5 September 2013

Baby steps on a big bot

Since I have been back from camp, (see older posts) I went down to my favourite sketchy discount store, the same place I got the chassis for autosquared and A2, and found two functioning motors, plus the rear axle from this: A "Power Wheels" brand toy car.
The cool thing about power wheels cars is rather than having just one motor driving the rear axle which would turn the wheels, they have a solid non-rotating rear axle, whith a motor mounted on either side, each driving it's own wheel. This makes them ideal for building a nice "tail dragger" style differential drive robot. I present to you a rough mock-up:

The wheels you see are not even close to the size I will be using, I will probably use something like large walk-behind lawnmower, or wheelbarrow wheels for the drive wheels, and a nice large pneumatic castor for the tail. To connect the drive wheels to their motors, I plan to drill 6 equidistant holes around the main axle hole on the drive wheels, thread 1/4" bolts and nuts thru them so they stick out the side, and let those 6 bolts sit the depressions on the side of the motor output hexagon-type shape, I will then fit a sleve made from 1/2 of a 2" PVC pipe coupler around the bolts, preventing them from popping out of the depressions. Depending on how much stress I think those hexagon-ish shapes will take, I also have some metal pipe bushings that I plan to file the outer threads off of, which will make it fit perfectly in the centre of the output drive, while still letting the axle pass thru, to prevent them form collapsing under the stress, and I may tighten some pipe clamps around the PVC coupler, to prevent it from cracking outward and breaking. Have a look at a couple pics:

I am planning to use the motor controler I built for my bot "GPS" and a 12V 35 AH SLA battery to drive the motors, the motor controler should have no problem handling the current, and seems to be well-suited for the purpose, and the battery should provide me with some decent runtime, whithout being too heavy, 30 lbs-ish.

The mock-up picture shows my nice solid-state computer, and a night vision security cam, both of which I plan to add at some point, but for now my short-term goals are to get it driving by remote control, and possibly avoiding obsticals by its self once that is acceived, and possibly get my paintball gun mounted on it (do I see a remotely operated, night vision equiped, green laser aimed, semi-auto paintball marker bearing platform in my future? AWWWWW YEAHHHHHH) but I get ahead of myself :) later goals include getting that computer on there, with a webcam or two for machine vision, getting it navigating via GPS and compass on its own, and maybe making it auto-aim with a couple PIR sensors. But like I said, those will be later, much later. Grand ambitions for a pile of parts laying on my floor. Also, I forgot to mention, the frame will probably be made from some more PVC or ABS pipe and fittings (I love my plastic pipe!) with a skid plate made from an old stainless-steel dishwasher front cover. Excitment.

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