Friday, April 11, 2014

New Model Renderings

The new model is almost done. I've got some renderings together to give an overview of the design.

In this version I'm making use of flat plywood parts from a CNC router as well as 3D printed pieces for the gearing and brackets on the primary mirror.



The gearing used follows the design of some printable Reprap extruders which make use of a herringbone tooth pattern to avoid backlash.
The printable motor gears are very similar to the Reprap extruder design. The large azimuth gear is printed in sections and assembled on an aluminium plate which also provides the running surface for the bearings.

Now I just need access to a CNC machine and a bunch of ply. I'm going to start a git repository of all the cad files (solidworks format) so others can use them. Perhaps someone else will even beat me to the first build.

Monday, June 20, 2011

Now that I have a new PC I've started work on the CAD model for a new version of the AredinoBeam. The concept behind this design is that a large amount of the components will be laser cut from acrylic and plywood for easy production. I'm also getting familiar with the new 2011 generation of SolidWorks.

Monday, December 6, 2010

Tracking Timelapse

I've put the below primary mirror offset compensation calculations in place, and the rig it tracking well! I made a little timelapse with my webcam behind a pair of sunglasses to prevent overexposure outside.

Thursday, December 2, 2010

Tentative Solution to the Offset Mirror Problem

After tackling the cad model in a different way it became clear that the tips of the incoming ray vectors all lay on a circle offset from the circle traced by the centre of the elevation mirror. Knowing this and using some similar triangles I came up with these two equations:


az = sin-1(sin(off)/cos(e))
em = tan-1(tan(off).tan(e)/(sin(az) + tan(off).cos(az)))

where :

az            =             additional azimuth angle added by primary mirror
em           =             required elevation of the primary mirror
off           =             offset of the primary mirror from centre
e             =             calculated elevation of the sun

Now the required machine position can be calculated from the elevation and azimuth angles of the sun.

Wednesday, December 1, 2010

The Source of the Error

Because of the way the primary mirror is offset to prevent shadow being cast onto it from the secondary mirror, it turns out a few complications occur. The adjustment of the primary (elevation) mirror angle effects the azimuth alignment because the reflection plane is not vertical (as it would be if both mirrors were in line). To solve this I need to be able to calculate the two angles marked 'x' and 'y' from the elevation angle E and the mirror offset (currently 18.4deg). I know that the angles 'a' are equal (this is the path of a ray in the plane of reflection).

I have had a go at this but so far am struggling with the derivation. I assumed that the solid lines were of known length (1 for convenience) but this may not be necessary. If anyone feels inspired please give it a crack and let me know how you get on!

Thursday, November 25, 2010

I have finally got the psa algorithm to match the NREL code. Not really sure why I got the errors in the previous post but I suspect it was to do with the inputs I gave the NREL calculator, and not with the simpler psa code. Anyway now I'm getting results that match within ~0.5deg. However I am still having issues with my rig drifting out of alignment over time.

I did a little experiment today and set up a sundial with a thin vertical stick in the centre. I marked the position of the shadow with the current calculated azimuth value and waited for the calculated angle to move 30deg (2hours from 1:30 to 3:30).

The rig tracked nicely around 30deg but had over-rotated and was casting a shadow. When I came to measure the new shadow position on the sundial it was only about 20deg from the old mark... So the results that I'm getting from both NREL and the psa algorithms aren't matching what's happening in the real world.

I have a new piece of code from gabriel over at http://www.cerebralmeltdown.com/, which works from tabulated data. I'll give that a go and hope for the best.

Finalised Circuit in Place

I've just finished transferring my prototype bread board circuit to a more permanent soldered perf-board setup. Been having issues with bad connections here and there so this should finally sort that out.




Also added a circuit diagram page done quickly in publisher.