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BUILD YOURSELF A WINDMILL GENERATOR Part 3: the windmill platform – by Glenn Littleford* The windmill platform has to perform several tasks. It must support the thrust and weight of a propeller, support the alternator and drive shaft from the propeller, include some sort of tail furling system, provide a mounting point to the tower, be strong enough to survive high winds and it must be easily maintained and modified. If possible, it should also allow some means of getting the generated current from the alternator to the ground without the power leads becoming twisted, stressed or breaking. 100  Silicon Chip siliconchip.com.au T his windmill platform is available as a kit consisting of laser-cut steel parts, stainless steel nuts and bolts and a set of new bearings. The steel sections are grade 250 mild steel, 8mm thick, and designed to fit together easily. Also included are the 4mm steel propeller hub plates, machined propeller adapter, a 200mm length of steel rod and a 100mm length of steel tube (these form part of the propeller hub and tail assembly). Not included with the kit is the tail boom, a 1000mm length of 22mm steel tube, or tail. Why aren’t they included? Well, the whole kit packs into a 350mm square box for delivery. If the tail boom and tail was included, a much larger package would be needed and the extra delivery costs would far outweigh the cost of the tail parts themselves. You can pick up a length of 22mm steel tube for less than $10 new (or from the local scrap metal yard for a couple of dollars) and the tail fin can be made from a small sheet of scrap plywood or steel. The tail boom and tail fin (3mm aluminium, approx 600mm by 500mm) can be included with the windmill kit if requested. If you decide to make your own tail fin (and I recommend you do), why not get creative with your design? I’ve seen tail fins shaped and painted like chickens, pigs and cattle dogs. Fig.1 shows the windmill platform parts. The platform is designed to be easily assembled. You will need only some basic tools and access to a welder. There are two new bearings included with the kit: a 6005 (which is the same one F&P use in their washing machines); and a heavy duty 56205 bearing and F205 carrier to support the weight and thrust of the propeller. The windmill platform is designed to be bolted onto a car wheel hub at the top of your mast. We are using a car Tack and weld the hinge tube and tail boom to the tail brace. *www.thebackshed.com siliconchip.com.au Fig. 1: view of all the laser-cut steel parts making up the windmill platform. hub for strength and reliability. Car hubs are designed to carry over a ton so you will never need to worry about this bearing failing, But there is a disadvantage: because we use a car bearing our drop wire needs to feed down the side of the windmill Mount the base plate in a vise, fit and tack-weld the front and rear bearing supports. Check they are square before fully welding. February 2005  101 Fig. 2: alternative to using a car hub bearing. If the wind in your area changes direction several times a day you might need to use a yaw bearing like this. Fig.3: top view of the windmill platform showing the stator and bearings placement. and mast, not down the middle of it. So after a few wind changes (a windmill changing direction to face the wind is called a “yaw”) you may find your drop wire wrapped around the mast. On my windmill I have a rope tied to the tail with a tennis ball attached to the end that I can reach from the ground. About once a week I grab the tennis ball and walk the windmill around to unwind the drop wire. The rope is also handy to point the windmill in one direction by tying the rope to a tower guy wire. If you are in a location where the wind changes direction several times a day, you might want to look at another option (see Fig.2). Using this design you can feed the drop wire down the middle of the mast, allowing the windmill to spin around several times before the twist in the drop wire becomes a problem. Occasionally you would still need to untwist the wire. This approach is not as strong and reliable as the car bearing. A better option still would be to use the car hub and bore a 10mm hole down the center of the stub axle. Doing so shouldn’t weaken the hub enough to be a concern, but you will need access to a good lathe and some sharp drill bits as stub axles are very hard! Fit the hinge rod, short and long hinge plates and tail stop plate, tack and fully weld. Once the weld has cooled, clean up the metal work with a wire brush, then apply a few coats of paint to prevent rust. 102  Silicon Chip siliconchip.com.au Commercial windmills overcome the yaw problem by using a set of slip rings and brushes to connect the drop wire to the windmill. This is a little complicated to explain here but it has been done by windmill enthusiasts. I’ve chosen the common Holden hub pattern for this windmill as these are readily available from trailer supply outlets. If you have another hub pattern that you want to use, the kit can be supplied to suit at no extra charge, providing the hub diameter does not exceed 140mm. The tail used on our windmill is of the self furling type, which means the tail is designed to turn the windmill out of the wind if the wind speed or load on the windmill blades exceeds a safe point. So how does it work? You will notice the windmill propeller is offset to one side of the mast by exactly 100mm. So as the wind blows against the propeller, the whole windmill will want to turn away from the wind. Our tail is on a hinge of sorts, angled back and angled out to the opposite side of the propeller. This angle means the tail wants to turn downward and out (just like when you are asked to move a mate’s fridge, as soon as you lean the fridge back the door opens and gets in the way ). We have placed a stop on the hinge, so the tail will stop when it is pointing directly back from the windmill. When the windmill in running in normal winds, the weight of the tail is enough to keep the tail against this stop and therefore keep the propeller facing the wind (remember the tail will always be downwind). As the wind speeds up the force against the propeller will reach a point where it exceeds the weight of the tail. The propeller will start to turn out off the wind and the tail will turn upward on the hinge. While gravity wants to pull the tail back down, the force of the wind keeps the tail downwind, where it balances against the force of the propeller trying to turn the windmill around. As the wind picks up the tail will lift higher, until it reaches the top hinge stop. At this stop the tail is almost in line with the propeller, which is almost at right angles to the wind. The furling is adjusted by adding or removing weight The bearing, bearing plate and spacer plate fit into the stator as shown. The gap in the spacer plate is to clear the welding on the rear bearing support. siliconchip.com.au from the tail or changing the tail boom length. If you find your windmill is turning out of the wind too early, try adding some weight to the tail, or move the tail further out (and vice-versa if the tail doesn’t furl early enough). This method of furling is very simple and reliable and has been in use for hundreds of years. Putting it all together. Included with the windmill kit is a full set of detailed instructions but I’ll show you the basics here to give you an idea of how the windmill is assembled. All the steel parts in the kit are laser cut. Laser cutting leaves a loose flaky edge on the steel, and this needs to be removed – easily done with a wire brush or coarse sand paper. Also check that the 6005 bearing fits into the bearing plate. As this part is laser cut it should be a nice fit but sometimes parts are a little too tight. If so, grab a metal file and file off any excess metal until the bearing slides snugly into the adapter. Secure the base plate in a vise and slide on the front and read bearing supports, then tack-weld together. Check all is square before fully welding (either stick or mig welding is fine). Allow to cool before proceeding. Next fit the tail stop, short and long hinge plates and hinge rod to the base plate and weld together, making sure you have the tail stop plate the right way around (see Fig.1). You will also need to weld the tail brace to the hinge tube and tail boom. If you use a length of galvanised pipe for your tail boom, be warned that welding galvanised steel gives off some very toxic fumes, so use a gas mask with suitable filter and weld in a well ventilated area. Once the parts have cooled down give them a going over with a wire brush to remove any welding splatter and slag, Then paint them with a good metal paint, such as “Killrust” or engine enamel. Press the 6005 bearing into the bearing plate. It will sit flush on one side but on the other side, the side which fits into the F&P stator, it will poke out 4mm. Using the four 6mm bolts, fit the stator retaining plates, stator, bearing plate and sparer plate to the rear bearing Almost finished: the stator, drive shaft and front bearing fitted. February 2005  103 support on the windmill platform (see Fig.3). Now slide in the drive shaft from the front until it pokes out the back of the stator, screw on and tighten the drive shaft retaining nut, and then tap the drive shaft forward until the retaining nut is home. Add a drop of Loctite to the retaining nut, being careful not to get any on the bearing. Next slide on and secure the front bearing using the four 12mm bolts. The front bearing has a grease nipple, so pump in some bearing grease to fully lubricate the bearing, then tighten the two grub screws onto the drive shaft. Check that the drive shaft spins freely. If there is any resistance, loosen and re-tension the stator bolts. Now screw on the magnet hub. The hub is designed to mesh with the shaft spline while the plastic retaining nut will slowly feed the hub over the stator as it is tightened. Try rotating the hub to check that the hub is not binding against the stator. You should feel a distinct cogging as the hub rotates – this is normal. Be aware that the stator will be generating electricity as you rotate the hub, so treat the connections as live and possibly shocking! Mount the windmill level. I use a “test stand” for this. It’s basically a mast about 1.5m high. Apply a little grease to the tail rod and slide on the tail boom, making sure it can rotate freely. If it’s a little tight, remove any burs or seams inside the tail hinge tube with a round file. Now with the windmill level and the tail pointing directly out the back of the windmill, position the tail fin on the tail boom, clamp with a couple of G-clamps and check that it is straight up and down. Then mark and drill the tail fin bolt holes. It’s not critical that the tail fin is vertical but it definitely looks better. cool breeze, plus you only need to run two wires from the windmill to your battery’s positive and 0V terminals. If you place your rectifier near your batteries, you will need to run three wires from the windmill (or six if you plan to experiment with delta/star configurations) but you won’t have to worry about water ingress into the rectifier or taking your windmill down if the rectifier fails. The windmill base plate includes a few extra bolt holes for mounting the rectifier, and a 20mm hole to suit the supplied cable retainer to support the drop wire. The kit The windmill kit is available via my website, www. thebackshed.com The web site includes detailed instructions, a bunch of photos of my windmill creations, and other windmill projects including a “Mini-Mill” using a stepper motor from an old PC floppy drive. SC Next month In the final part to this series, we will look at a couple of propeller options, basic propeller blade designs, and some options for a mast. Mounting the rectifier As we mentioned last month, the output of the windmill is AC and you need to rectify that to DC before using to charge batteries, etc. You can mount your rectifier either on the windmill (at the top of your mast), or at your battery bank. One advantage of mounting on the windmill is that the rectifier is up in a Screw on the magnet hub and check that there is no binding or scraping. Remember the stator terminals will be live while the hub is rotating. 104  Silicon Chip With the windmill mounted level, fit the tail boom and align the fin vertically, then drill and bolt to the tail boom. siliconchip.com.au