The key to building a good rotisserie is to give some consideration to the type of meat you are going to want to barbecue. You can build a rotisserie capable of roasting a 200 pound (90 kilogram) hog, or a small chicken, so decide what your goals are early on. If you want a rotisserie that can handle the biggest jobs, you should consider building one from scratch. One good way to accomplish this is to use a 55 gallon (200 liter) drum that has been cut in half, and then weld together an iron frame to set on top of it. If you simply want to spit-roast smaller cuts of meat on an existing grill, you should build a frame that matches your grill, and attach a small direct current (DC) motor to turn the spit.
Whether you want to build a rotisserie from scratch, or retrofit an existing grill, most of the same general principles will apply. The basic components you will need are a heat source, such as a fire pit or grill, a frame, a spit, and a motor. Before you begin the planning stages, you should first decide what type of meat you will want to barbecue on your rotisserie. The type, and more importantly weight, of the meat will dictate exactly how strong your rotisserie needs to be, as well as how high it will need to be above the heat source.
If you want to be able to barbecue a full grown hog on your rotisserie, the best method is to start from scratch. The first component you will need in this case is a fire pit, and a great solution is to simply use an old 55 gallon (200 liter) drum. It is important to choose a drum that was filled with a non-toxic substance like cooking oil, so avoid any drum that you cannot trace the history of. If you saw a drum in half, then cut out vent and drain holes, it will function as a great fire pit for your rotisserie.
In order to build a rotisserie capable of barbecuing a whole hog, you need to ensure that your construction materials and methods are sound. The best foundation for a rotisserie of this size is a welded metal frame that can be set right on top of the open fire pit. You should then obtain a metal pole strong enough to hold a substantial amount of weight, and an electric motor capable of putting out a good amount of torque. If you build a rotisserie of this size with a hand crank, you may find it difficult to use.
Another way to build a rotisserie is to make use of an existing gas or charcoal grill. If you want to be able to spit roast chickens, pork butt, and other similarly sized meat portions, this can be a good option. Some grills even have existing mounting hardware for rotisseries, so the first step is to determine whether your grill does or not. You should then construct a small frame that is strong enough to hold the weight of the meat you will be roasting, and then fit it with a spit connected to a small DC motor by a belt and pulleys. In order to make sure your rotisserie turns at the correct speed, you can adjust the pulley sizes until you achieve a rate of between about one and five revolutions per minute.