During the past week I have been solidifying the design and spending lots of time scouring the net for parts and scrounging locally. Although I have a pretty clear picture of what I need to do, I am having significant problems finding affordable parts. I need things like high torque gearboxes and large structures that can withstand high winds, and they just are not cheap, especially since they must look good. Consequently, the design is going to have to adapt to whatever I can find. Somehow it is going to have to look professional or I won't be allowed to install it in the front yard.
Because this project is budget constrained (I cannot afford to spend hundreds or thousands of dollars) the design is not being done in a classical way – it is morphing to accommodate affordable parts I find that might work. It means the detailed design cannot be fully completed yet, but ordering of parts must proceed to allow for long delivery times. So I have ordered a mess of affordable parts that I have managed to source, but they are also rapidly adding up.
Some detailed design work can be done, for example I have designed the motor mount bracket for the BLDC motor that comes with the kit. Here is a picture of it:
The system will have a large mirror to redirect sunlight to a target area. The mirror will rotate around a horizontal axis to provide a desired elevation angle. The elevation motor to drive this rotation will be geared down to provide high torque at low speed. It will employ a worm gear so that the position will remain fixed when the motor is off. I have obtained a gearmotor with a worm gear that should be adequate for this task. I have also obtained a timing belt and pulley to provide even slower rotation with higher torque.
The mirror and elevation motor assembly will be rotated around a vertical axis to adjust the azimuth angle. The azimuth motor will also be geared down with a worm gear to ensure nothing moves when power is not applied. This motor will likely be the BLDC motor in the challenge kit, as long as I can rig appropriate gearing. So far I have some flex couplings, but no suitable gearbox. The 24 volt motor power supply has already be acquired, but I will likely need to rig up a big FET to cut power to the DC converter when it is not needed. The motors may only need to run briefly every 10 minutes or so.
There will be a solar cell panel that charges a battery that will be used to power the NXP controller and motors. The solar panel orientation will be helped to be more directly facing the sun by the azimuth rotation. I have obtained the solar panel, but no mounting hardware yet.
The controller will measure elevation using a tilt sensor already on the Kinetis controller card. I am hopeful the on-board magnetometer will be able to measure azimuth (compass) angle, but if not I have a separate compass module that could be used.
The controller will communicate via Bluetooth to an android tablet which will be able to swivel the mirror or program a target area to stay focused on. I have procured an HC-05 bluetooth module for this purpose.
Since snow removal is not needed in the summer, I may put solar panels on the back of the mirror to allow it to be a solar tracking solar panel. I also want to try it as a device to turn any window into a skylight - redirecting sunlight through a window.
I realize this is a bit dry reading - hopefully I can sketch all this out soon, but right now my computer with drawing software is fried and we are still expected to blog weekly.
Relevant Links
The full set of Clear Walk project blogs can be found here:
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