|Solar Tracker Construction|
We sourced most of the material from the local scrapyard, mainly because it's cheap and they had what we need. They sell steel for 40c/lb, which is a whole lot cheaper than buying it new (and some of what they had was in like-new condition anyways). The main items were the 8" schedule 80 steel pipe that makes up the mast and the 5/8" steel plate that makes up the base and parts of the polar mount. This stuff is so heavy, it's pretty difficult to move around. The chunk of steel plate we got weighed about 500 lbs! I cut it into the neccessary pieces without ever moving it off the trailer (thanks to Don Kay for letting us borrow that).
I was a little concerned about how well my little 220v MIG welder would penetrate this heavy steel, so I did some practice runs. I bevelled about 1/4" off each edge, so that makes for a pretty heavy root weld.
It seems to penetrate pretty well though, and after a few opinions from other welders, I decided it's probably good enough :-). I started by cutting out all the pieces from the 5/8" steel plate. You have to be pretty steady with the torch to get a decent cut; I like to use a piece of angle iron as a guide to keep you going straight. It takes a long time to grind something this thick, so care using the torch definitely pays off. Here's some of the finished gussets:
These guys will go between the mounting plate and the mast for additional support.
One more for a bit of a size reference...
This will be one of the the sides of the polar mount. Imagine that piece of 5" pipe in between these, with a pin holding it up (it'll make more sense in a minute).
One more of all the pieces together. The large square piece in the back will be the base, the long piece with rounded corners will be one of the endcaps, the two long, triangular pieces will be the frame mounts, and the 3 pieces in the front make up the base and sides of the polar mount.
Here you can see the polar mount base coming together. That's a 2" hardened steel pin going in between (it took about 20 minutes to cut through it with a chopsaw). We had a local machine shop bore out the holes in each plate and cut a grease groove in the bearing surface. Although it really won't move much (this will be the hinge too allow for manual elevation adjustment), it's probably still a good idea to keep everything in good shape. There'll be zerk fittings on top of each plate. The real trick here was trying to keep those plates perfectly perpendicular to the base (and parallel to each other) while welding them on. There's only a few thousands clearance between the bearing surfaces and that pin, so it's got to be pretty close. In fact, it was just a big darn headache, and next time I'm sure it'd be better done with flange bearings bolted to the plates since they allow quite a bit of freedom in alignment.
Here's a few pictures of the welds going down between the base and the sides of the assembly. Again, I bevelled about 1/4" off each side of everything to maximize penetration. For extra insurance, I preheated everything to about 450F with the torch. In the end, there was lots of discoloration on the opposite side of the weld (which usually indicates decent penetration) so it was worth it.
And then 2 more welds on top of the root weld...
Now here's the hinge tube in between the plates. This will be on the north-south axis, and the array will track into and out of the picture. It's at about 40 degrees of elevation in the picture, so that's where it would be sometime in the spring or fall.
And now, these pieces get added to the hinge tube. That rod on the left is the other piece of that 2" steel pin I mentioned earlier. We had 2" holes bored through each of those endcaps, and the pin slides through and is welded in place. The whole array will then pivot on that pin.
Here's the endcap welded on. You can see the steel pin "tacked" in the far right.
And here it is all finished! You can see how the far right endcap is pulled in to the left; it's amazing how strong the weld shrinkage is. The array frame will bolt to each of those flange bearings in the center. The flanges are built such that the bearing can pivot about 15 degrees each way, so they don't have to be aligned perfectly. That's enough pictures for one page, so onto the next one...