The drum roaster is the most common coffee roaster design, probably due to its simplicity: a metal drum is spun over heat like a spit on a campfire, cooking the coffee beans loaded inside.
Many drum roasters sport huge capacities, roasting anywhere from ten to several hundreds of pounds of coffee at a time, but there aren't many small-scale drum roasters out there. With some research, we were able to track down and purchase a mysterious drum roaster called the Huky 500. It's so mysterious that we still don't know how to pronounce "Huky" five months later.
The Huky is designed like a large scale drum roaster that's been shrunken down to hobbyist size. There are just over 1,000 in circulation. Ours is #1096. It is designed and fabricated (I think) by one man: a retired engineer on the other side of the planet, who is almost certainly insane.
As with most drum roasters, the Huky has four key components: heat, a drum, exhaust, and cooling.
The heat source is a propane-powered stove. The Huky sits atop this stove, straddling its brilliant blue flame. A simple knob allows you to control the size of the flame, and thus the amount of heat it blasts onto the bottom of the drum. You can use other heat sources as well. I've read of people using the gas range on their kitchen stove.
The drum is where the coffee beans are loaded and where roasting actually occurs. The drum is kept spinning by a motor in the back, while several blades inside keep the beans constantly mixing. All of this prevents beans closest to the heat source from getting scorched and ensures all beans are roasted evenly.
An exhaust system is necessary to deal with the absurd amount of smoke generated while roasting coffee. For the Huky, this is just a fan that sucks air out of the roasting drum. As you know, coffee beans also release pesky chaff flakes during roasting, which tend to get sucked into the exhaust system. A sieve attached to the exhaust fan collects the chaff in one place for easy disposal.
Finally, the cooling tray's sole purpose is to rapidly cool the coffee beans to room temperature once they've finished roasting in the drum. The Huky just uses another fan/sieve combo to accomplish this: roasted beans are dumped out of the drum into the sieve, and the fan underneath draws air through the beans to cool them off.