Saturday, July 21, 2012

TOBL2: Frame Design Complete!

About two minutes ago I placed my first Big Blue Saw order. This included all* of the missing pieces for TOBL2's frame which will be water jet cut from 1/8" 6061 aluminum plate. I guess one benefit to making everything so absurdly small is that I save some money on these sort of orders. Before shipping it came out to $81.40, which I hear is about the minimum you can pay. I like how Big Blue Saw gives you a preview of what your parts will look like if they were flying through a dessert.

Keeping this guy compact took a lot of changing dimensions, looking at the part in assembly, and then fine-tuning the dimensions further. The motors are mounted to a plate which can pivot, so that eats up a lot of space. The electronics stack also grew a little with the addition of the motor controller board. Altogether though, I'm very pleased with the way it turned out. The center of mass is going to be pretty atrocious, but I'm not ready to start selling TOBLs just yet, so that's alright.

I did away with the three aluminum posts mounted at each corner, and added two shelves. The top one is for the electronics stack (shown transparent) and the bottom one will hold the battery pack (ditto). PCBs should never be structural components, as I'm learning so well at work this summer. In this case, I had to be very creative, since the axles are now live and attaching posts to them won't work anymore. I prefer the old bulky aluminum posts mechanically, but I ordered an extra electronics shelf beam, so I can always put that above the servos if this doesn't cut it. As you can see, I had a little fun with the battery shelf.

Sexy battery tray

A lot of what took so long designing this frame was also anticipating what's going to go wrong. Having a drivetrain with triangular geometery, belts, springs, and moving motors, is really just asking for it - in terms of alignment issues. In an attempt to resolve all this, I put some redundant holes in to allow a little tuning upon assembly. For example, all those holes in the motor bracket are to adjust the spring tension (not easy to see in the picture below).

The drawing geometry and dimensions for these plates are disgustingly complex

 See what I mean? Gross

I also ordered some bearings on eBay, which had no picture, so that's always good. They were a dollar a piece though, so if they're the wrong size then I'm sure I'll create some crazy thing which will need them down the road. The asterisk in the second sentence is because as hard as I tried to make this the entire frame from the water jet order, I'm going to need to machine a few thicker (1/4") blocks at the interfaces of the plates and shelves. These are really straight forward, so hopefully the machinist where I work will be kind enough to let me knock those out some time.

Also, just bought a road that may have something to do with why TOBL had been moving so slowly recently...

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