Wednesday, June 22, 2016

Solar Tracker

Making a solar tracker for a solar cooker or solar panels is easier than you may think. You could design one that uses a micro-controller or complex circuit. But, it can also be done with JUST small solar panels and a DC motor.

The concept is simple. You have two or four small identical panels that are each powerful enough to spin a small DC motor. There is a divider between the panels that cast a shadow when the unit is not pointing directly at the sun. The panel that doesn't have a shadow cast on it produces all the power and turns the motor. As the shadow starts to minimize, the other side's panel starts applying reverse current to the motor and slowing it down.

You could have more than one panel each side, as shown below.

Something to remember is that the motor will have to be geared down so the output is lower. Or you can find a geared motor, such as a windshield wiper motor. You could also use a smaller motor and just use a string wrapped several times around the spindle or capstan of the motor. The rest of the string would wrap around a wooden pulley or disk from both sides. And, of course, the string would be stretched taut.

Monday, June 20, 2016

Make your own powerful and simple alcohol stove

I uploaded a couple of videos testing this stove and some people have asked for instructions on making this. It is very quick and easy to make. Have fun!


Wednesday, June 15, 2016

Weird way to furl a windmill

I was watching a video on youtube where supergokue1 was running a double windturbine on one mast and connecting the motors in series to get more voltage. The test didn't produce as much voltage as he had hoped, but I had an interesting idea about furling this windmill under higher wind conditions.

SuperGokue1 on

The idea involves a physics concept called gyroscopic precession. This is a phenomenon occurring in rotating bodies in which an applied force is manifested 90 degrees later in the direction of rotation from where the force was applied. We use the right hand rule to determine the torque direction or spin vector.

Applying the right hand rule to the double windmill, based on direction of blade rotation, means that the spin vector is a force acting outward towards the wind. Each blade set is doing that so both forces are balanced. But, what if you design one of the blades so it spun in the opposite direction? And, then, you make the tail smaller? 

The result would be that higher winds will cause the windmill to yaw out of the wind slightly. This will slow the blades down, then gyroscopic procession will decrease as the blades start to spin back into the wind and the process repeats...until a sweet spot is found. This should work nicely for small fast spinning wind turbines. This should protect them in higher winds. Just imagine 40 mph winds while the wind turbine is furled sideways at a 45 degree angle and still producing safe power.

Sunday, June 12, 2016

Survival Lilly Survives Canada

Survival Lilly came to Canada....and survived. She spent about a week in the bush, practicing her bushcraft and survivalist skills. The helicopter picked her yesterday, and yes, she was in one piece. Unfortunately, we have to wait a few days to see her video updates. I can't wait to see those.

We gave her a ride to the BC-Ferries terminal today. I have a nice Survival Lilly patch to show off now. But, don't worry, she left with a Canadian flag patch of her own. Now, she is off to her next secret survival spot to live the adventure. Rock on Lilly!

Friday, June 10, 2016

VAWT (Savonious) Wind Turbine Calculator

I have done some work on my VAWT / Savonious Wind Turbine Calculator. It allows you to enter parameters and compute power output, amperage to batteries or the grid, cut in speed, etc. The program can be found here.

You start by selecting a battery voltage; 12, 24, or 48 volts. Alternatively, you may select 120 or 240 volts for grid tie. Weather conditions default to "moderate", but you may calculate for summer or winter as well. This is important because the temperature and density of the air can have a profound effect on the generator's cooling and therefore its maximum power output.

You can then enter the overall blade width. This is the width of the turbine as seen by its profile, not just one blade. Then enter the blade height.

The Gear Ratio field is used when your generator needs more speed to produce a usable voltage. Wind speed is entered in miles per hour. The calculations are based on this wind speed.

Tip Speed Ratio (TSR) is how fast the tips of the blades move in comparison to the wind speed. A typical horizontal axis wind turbine (HAWT) is usually between 3 and 10 TSR. A typical VAWT such as a Savonious is about 0.8.

The Blade Efficiency field also represents the Power Coefficient. A well-designed 2-blade Savonious has about a 24% Power Coefficient. A 3-blade has about 15%, although it does have more torque and works better at less than 23 mph or so.

The motor/generator's amp, volts, and RPM rating are usually given by the manufacturer. The generator's efficiency is a little different. Typically, a permanent magnet DC motor with brushes is about 50%. A three-phase permanent magnet alternator is about 75%, and an AC induction motor is about 90% (used for grid tie).