HOWTO Build Your Own Bicycle Rotisserie: Part II
In Part I I discussed the inspiration for the bicycle rotisserie and laid out a bill of materials. Now we get down to the nitty gritty of actually building the thing. So without further ado… The first thing you need to do is pick a master bike and a slave bike. The slave bike doesn't need to have a functioning chain or sprocket setup, or a rear wheel. So pick whichever one has a nicer chain, sprocket, and dérailleur to be the master bike and remove its shifters from the handlebars. Next, remove the front forks from the bicycles. The way to do this varies from model to model, but typically there is a small allen-bolt in the center of the top of the fork tube, which you unscrew. This releases the tension from a small wedge mechanism that keeps the handlebars and fork together. With this bolt loose, you should be able to remove the handlebars and fork from the bicycle. Sometimes a gentle tap on the protruding bolt head helps unstick things. You'll also want to remove the seats from bicycles and the seatpost from the seat itself. The seatpost is usually held to the bike with a small pinch bolt, or with a quick-release fitting, depending how fancy a bicycle you're dealing with. Loosen the bolt or quick release and pull up on the seat. This may require a bit of coaxing, twisting, or WD-40 to accomplish. The seat itself is usually also held on with some kind of pinch bolt, which should let go of the seatpost when loosened. If you're lucky, the top of the seatpost will nest nicely inside the spit you've acquired. To allow for easy removal of the spit from the rest of the contraption, I used the seatpost ends to allow the spit to be unbolted. Basically this involved inserting the end of the seat tube into the spit and drilling a 1/4" hole through both. Later I inserted the 1/4-20 bolts in this hole and fastened it with the nuts. Next you'll want to cut the tops of the seat posts off so that only an inch or so of full-diameter tubing remains. You'll also want to cut off the pedal crank on the chainring side of the bottom bracket and weld the stub onto the chainring where the crank used to be. Putting some effort into getting it welded on perpendicularly will pay off later, but it doesn't need to be absolutely perfect. The remainder of the seatpost needs to be welded onto something that will give the bicycle firm footing when placed upside-down. I used an 18" section of square tubing welded crosswise onto the end of each seatpost. Once this is welded up you can re-insert the seatpost. Ideally you'll want the seattube and downtube on each bicycle to form and isosceles triangle with the ground, but you can vary the height somewhat by using the built-in seat-height adjustment. You need to find a suitable motor to power the thing. In my case I was able to visit the local recycled building materials place and pick up a used blower motor for $5. You want a single phase 120V induction motor with a rating of around 1/3rd horsepower (250W) and a speed of around 1500RPM (a 2-pole motor). A small pulley might be helpful, but I got away with just using the shaft of the motor to drive the belt with a little stick stuck through a hole that happened to be in the end of it. You'll need a fairly long belt (around 10ft/3m) to go around the rear wheel (from which you'll need to remove the tire and innertube. What worked for me was a length of surgical rubber tubing (available, oddly enough, from fishing supply stores). To make it into a loop I just stuffed one end inside the other and super glued it. Amazingly, it held for the duration of the cooking event. About the only thing left to do to the bikes is to defeat the freewheel and lock the chain tensioner in an appropriate position. You'll be turning the wheel in reverse, and driving the wheel rather than the pedals. This is a sort of double negative that means the freewheel doesn't really come into play. But the meat you're cooking is rarely perfectly balanced, so it'll want to lurch forward once every rotation unless you lock out the freewheel. This is as simple as running some wire around one of the sprockets and through the spokes. The chain tensioner doesn't work right when driving things backwards, so you'll want to lock it out as well, which can likewise be accomplished with some creatively placed wire. At this point you'll be ready for a dry run, followed by the actual cooking event. Stay tuned for Part III.