*(UPDATE) The swing set performed well at the Bay area Makers Faire this past weekend 5/21/11. Having replaced the 44 tooth driven gear with a 112 tooth gear we were able to produce around 9 volts consistently. At 6 volts we had 0.3 Amps and 1.2 Watts. We were able to run 12 volt LEDs well, as well as 9 volt EL wire, and a 9 volt electric keyboard at the same time. We believe that with an additional gear reduction we will consistently produce 12 volts. Look for it deep in the outer Playa this year. Here is a video of it at the Makers Faire:
Also, this is my first Instructable so please bear with me. Hope you enjoy it.'
This project was done in Collaboration with and would not have been possible with-out my good friend Ryan Alpers.
Also I would like to thank Reid Johnston, Matt Gil, and Baker, and the good people at Bearing Agencies in SF for technical insight.
And Thank you to Cork Marcheschi for the use of his studio and equipment.
*(UPDATE)I wanted to make clear that the magnet rotor plates are very heavy and act as a flywheel, smoothing but not "bumping" the power. Also the chain does not move back and forth, but in a single direction. The swingers only affect the drive shaft when they swing forward, on their return trip the roller clutches freewheel back, also allowing the swingers to regain momentum. Thank you for all the interest!
After building Hugh Piggott's http://www.scoraigwind.com/ Axial Flux permanent magnet motor and adapting it to a stationary bicycle, i wondered what else i could use to make small amounts of electricity. After polling friends and family for old play ground equipment, a friends parents donated an old swing set. It was built ages ago but super sturdy and after a little TLC it was ready for a new life.
The design was pretty straight forward, i used Mcmaster Carr and some local (San Francisco) companies for the machinery. It basically went together over a couple of weekends. I used Hugh Piggott's generator since i had already made it and like the design for low speed low torque applications, but i guess anything else like an alternator or treadmill motor would work as well.
Materials used included 4 pillow blocks, 4 roller clutches, 9ft of keyed drive shaft, standard steel tubing, around 20ft of angle iron, a lot of lag bolts washers and nuts, a rear bicycle hub with a disk brake attachment point, a couple single speed rear bike gears, some motorcycle chain, a bunch of shaft collars, 4 pipe collars, and a gear that fit the drive shaft.
tools used included a standard 110 mig welder, porta-band, files and rasps, rubber mallet, angle grinder, misc hand tools like screw drivers etc, drill press, hand drill, marine anti-rust spray, plumbers wrench, vise grips, and a motorcycle chain breaker and assembler.
Step 1: Deal With the Swing Set
In any event, it was 1/4' steel and built very ruggedly. Surprisingly after spraying some marine anti-rust into the joints and using a couple plumbers wrenches it came right apart.
After getting it back to our shop, we cleaned and removed as much built up rust flakes as we could. a stuck bolt led to drilling and re-tapping for a larger bolt, and all other hardware was replaced.
where some of the ends of the legs had warped over time where they went into the joints, we used an angle grinder to remove rust and round them out.
After re-assembling the swing it looked 30 years newer and went together and came apart effortlessly.
Step 2: Work Out the Design, Assemble Materials
We settled on hanging a drive shaft a few inches below the top of the swing by pillow blocks, and to attach the swings to that by roller clutches, (or roller bearings as some say. Essentially ratchets). as the swingers swung forward they would turn the shaft forward, and when they swang back the roller clutches would freewheel and the momentum of the generator would keep moving forward. if the two swingers were out of sinc. then there would always be someone pushing the generator forward.
The generator was to be connected to the drive shaft by gears and chain.
The picture shows when we thought we would be able to fit 3 swingers.
The roller clutches which fit around the drive shaft were to be pressed into a standard pipe, and the swingers chain secured to the pipe. that way the weight would be distributed over the drive shaft and the swings would be removable.
All in all the finished product came out very similar. which i don't usually expect.
Step 3: Assemble the Generator
As anyone who is familiar with Hugh Piggott's generator knows, it was designed to sit on a wheel hub from a cavalier or something. When i built it, instead of going for the wind turbine i opted to addapt it for a stationary bicycle. I actually got the idea to use a standard rear bicycle hub with disc brake mount from a website a long time ago, and it worked quite well.
There is a picture of the hub with out the stator and magnet rotors on it sitting in its eventual mount. in the picture you can see the aluminum scrap plate that i machined to mount to the disc brake attachment point and the holes where the lag bolts for the rotors attach. To get the rotors though i had to grind down the flanges on the hub. A pity, i don't like destroying things.
The beauty of this system is that it already has built in bearings and a massive amount of free parts like single speed gears readily available. Which made finding chain etc easy. I wasn't sure if the disc brake could handle the weight of the magnet rotors which weigh at least 45 mounds, but the hub takes it like a champ. I think using a mountain bike bub (which is more likely to have the disc brake attachment anyway) is the way to go because it may be beefier.
basically, the magnet rotors sandwich an independently mounted stator with the copper coils, and the magnet rotors spin around it and the magic electricity fairies do their thing.
the other pictures are the stator mounted on the swing, the assembled generator, and a magnet rotor mounted to the hub.
Step 4: Attach the Drive Shaft
The drive shaft needed to stick out one of the sides of the swing to allow the gear to rotate and the generator to be mounted so the shaft had to be just lower than the joint where the swings legs attached.
I set the top of the swing set upside down on a level surface with the legs removed. Pieces of angle iron were cut to the length of the pillow blocks and drilled, then the pillow blocks bolted to them.
The pillow blocks and attached pieces of angle iron were then pressed onto the drive shaft and the drive shaft coupled together. two blocks and angle iron were welded to the joints on the swing at equal points to make the shaft level.
Next the remaining pillow blocks were supported by additional pieces of angle iron beveled to fit the swing set and after eyeball leveled, welded to the swing.
The drive shaft was then removed from the pillow blocks by de-coupling and sliding out.
Step 5: Assemble the Swingers Chain Attachments
The roller bearing/clutch act like a ratchet allowing the swinger to turn the shaft in one direction and let the shaft freewheel in the other.
I used a piece of pipe with a slightly smaller Inner Diameter then the Outer Diameter of the roller bearings.
The roller bearings were about an inch and a half wide so i cut the pipes 5 inches wider then the width of my shoulders.
After filing the weld ribbon on the inside of the pipe down to make the interior smooth and only slightly smaller than the Outer Diameter of the roller bearings. We used a half round file.
We then cut short pieces of scrap 2x4, and a hole was cut slightly smaller then the OD of the pipe. These blocks were then cut in half and used to hold the pipes vertically in a table vise without destroying the pipes.
once very secure in the vise, a Portaband (hand held steel bandsaw) was used to cut vertical lines length-wise on either side of the pipe, about the length of the roller bearings.
The roller bearing was then placed on top of the pipe while still in the vise, and with a wooden block on top of the bearing gently knocked into the pipe with a rubber mallet.
WARNING! when you put the second bearing into the other side be very sure that the bearings roll and stop in the same direction as the other side. They can be removed but you might not notice until you wonder why the shaft wont turn.
Plumbers clamps (circular steel belts with a screw that tightens) and hooks for the swingers chain were then tightened around the outside of the pipe and the roller clutches. (these were later welded after they tended to slip while swinging.
Step 6: Assemble Drive System
Take the completed pipes with swing attachment and pressed roller clutches,
A shaft collar for each side of the pipes, pillow blocks, and gear,
And the Gear,
And slide the drive shaft back through everything. Tighten the shaft collars after everything is where it should be, with the drive shaft sticking out one side and the gear on the outside.
Be sure to leave room for flailing arms and legs when swinging. on an eight foot wide swing, we found two adults fit.
Step 7: Mount the Stator
to account for experimenting with different gear ratios and not wanting the hassle of a chain tensioner, the distance between the generator and the immovable drive shaft gear had to be dynamic.
This led to the stator and the rotors being independently mounted on the same movable rig. where the rig was bolted to the swing legs, the angle iron had short "drop outs" cut to ease chain tensioning.
Besure to mount the stator as verticaly as possible, to account for the angle of the swing legs. This was accomplished with the use of a lot of washers.
Step 8: Mount the Rotors
The second picture is of the whole generator mount removed and fully assembled.
The generator mounted is then bolted to the swing.
Step 9: Attach the Chain
Using a motorcycle chain breaker and assembler tool, the chain is wrapped around both gears and the generator mount is moved up or down on the "drop outs" (like on a single speed bike right?) to adjust the chain tension.
The motorcycle chain is wider than bicycle chain but the same pitch as single speed. so that it didn't rattle or try to jump off a used two single speed gears with a spacer in between which fit very nicely. The drive shaft gear was the correct width.
Step 10: Enslave the Children of the Earth ( I Mean Swing)
It should at this point make some juice.
possible problems may be shorting the wires, or slipping roller clutches or swinger chain attachments.
In terms of swinger chain length, We found the sweet spot for power, was with pretty short chains, removing the impetus to make a huge swing. We believe that the shorter the chain the faster the drive shaft turns as there is less difference to cover for the swinger and the drive shaft has a fixed difference to turn. However if the chain is too short it is very hard to get into the swing, and more importantly very difficult to sustain momentum while swinging.
We got it producing around 4.5 to 6 volts DC with two large adults swinging hard.
The generator makes AC and some bridge rectifiers convert it to DC, that is the box of wires hanging out of the stator.
In the past this generator produced 12 - 13 V and ran a 300W inverter when attached to a stationary bicycle, though it could not be sustained for any comfortable amount of time. So I believe that in going with a 44/13 gear ration I was a little too optimistic. I am traveling for a few months but for those of you who might have thought this would make a good Burning Man project, your right, and we hope to get a stronger gear ratio on it by then.
As it is, we can not hope to power the mega sound system or persistence of vision video flashes we were hoping for, but we feel confident that it could at least light up some LED's and look pretty.
If you have read this and are interested I'd love to hear any ideas for what to power and how.
Hope you enjoyed my first Instructable.
Video coming soon...