This will roast a quart of coffee on a lazy Sunny afternoon, and is also good for roasting raw cacao beans, toasting grains and other yet undiscovered things. It has to be manually tracked so in other words you have to go out about every 20 minutes and change the position of the reflector. Until I can build a tracking system this seems to work fine for me because generally on a sunny day I am outside anyway. I have installed a stop button on the wiring to the motor and this is so that I can stop the basket from turning as you see in the video so that a portion of the beams will quickly toast and blacken. After a few beans are dark it seems to work more efficiently.
While the motor is rated at 24 V DC, it turns far too quickly at that voltage to be doing any good. I am currently running it off of a 3.7 V lithium battery, and have found that for this particular motor it runs at a really good RPM for doing this roasting. I have used it for quite a while and the lower voltage does not seem to affect the motor at all. It certainly seems possible that you could use other DC motors, like those from an old automobile that roll up the windows or some other DC type motor. In post collapse times there will certainly be a great abundance of auto motors to scavenge and use.
The focal point is quite bright and I highly recommend that if you use it focusing parabolic dish that you get some kind of welder’s goggles or polarized filter to look at it. Sometimes I forget and it really messes up my eyes.
I made the dish reflective by gluing on 2 inch mirrors bought online. Regular carpenters white glue works for this and it seems to hold quite well except every once in a while a mirror will fall out. I just glue it back on.
Parabolic dishes are quite ubiquitous and it is easy to make them reflective by gluing on strips of aluminum foil, or mylar, or mirrors which are unfortunately a bit expensive. They can also be used for starting charcoal briquettes, making char cloth and charcoal, and even heating up a quart of water to boiling and just over 20 minutes.