Non water wheel

I have read some old threads on here about water wheels and they have been a little helpful, but I want to ask about a wheel that doesn't use water. Let me set a mental picture. An eight foot diameter wheel that is more like a giant hamster wheel. The outside of the wheel has gear teeth. Engaged with the teeth is a generator. Basic ratio calculations 8' wheel to 4" gear at 7mph would run the generator. Generator I'm taking specs from is a gen that would hook to a pto of a tractor and runs 10kw. Now, the wheel would be built as close to balanced as possible and would be gotten up to speed from peddling a bike. I realize there may need to be some mechanical issues work out, but does the idea have any merit? This would only be a short term way to generate power. I'm thinking to charge batteries if solar or wind power hasn't been enough to build a full charge. Also, if use get the wheel spinning you wouldn't need to peddle only to keep it up to speed. Pick this apart I really want to know if I have a decent idea or if it's pure crap.

Hi Adam, I may be misunderstanding but basically you're driving a PTO generator with a bicycle?  The size of the wheel and sprocket just get the bike's speed to match the generator?  

I think the reason it will or won't work just comes down to the power needed.  I might be way off here but I think a 10kW generator takes at least 10kW to spin it and generate that power.  That's something around 13 horsepower.  I doubt you can generate that many horsepower on the bike.

If you use the bike to get the big wheel up to speed and then engage the PTO sprocket, I'm guessing it would be like putting the brakes on the wheel. It would decelerate rapidly unless you can provide 10kW to keep it turning.

No reason you couldn't use a much smaller generator that only needs the amount of power you can make on a bike.  Gearing it up or down with big wheels would be just fine.  I think multiple gear reductions would be easier than having one huge gearing reduction.  Belts and pulleys are also a decent way to transfer power across a speed change.

First off, I enjoy this type of pondering.  10 kw is roughly 17 horse power.  The wheel to me is a large flywheel.  Some of the flywheel generators that I have seen work spin about 200,000 rpm.  Some of these flywheel generators take all day to charge to speed to get 2-3 kw.  Flywheels can only spin to a designed rpm, because the centripetal force will pull the material apart.  Kinda like a top fuel going form 0-320 mph.  The tires grow an extreme amount.  I assume that the wheel will be going 7 rpm not 7mph.  At best, I can only pedal about 50w for 5 minutes on my homemade bike generator.  Flywheels will conserve energy, but as soon as you pull power it will slow down.  So my best at 250w per day it would take me 40 days to get it up to speed. Now if we look at inefficiency a gearbox that switches gear at best may be about 80% efficient.  So this would actually take 50 days.  As you pull the power from the system even at 100w I could only make half that up for 5 minutes. As the old engineer I worked for always said " power is power" Hope this helps.

The info I have looked at for the generator is 20hp and 540 rpm. The math I calculated a 4 inch gear on the generator with the ratio of an 8 foot wheel traveling at 24.5 rpm. 24.5 rpm equals 7 mph approximately. The wheel being heavy would take some muscle or a weight to get spinning but an object in motion is easier to keep in motion. So the 8 foot wheel being kept up to speed by the bike or a giant hamster. Could this be done and if so I would need to figure out how much weight the wheel needs to be. Too light and its easy to slow down and too heavy and I can't get it started. I hope that is more clear.

I think you're being clear and I think it won't run the generator for more than a few seconds unless you can apply 20 hp to the bike pedals to keep it turning.  

Regardless of the wheel, the problem is one of energy in vs energy out.  If the generator is consuming 20 hp of power, it needs to come from somewhere.  You can apply less power over a longer period of time to get a wheel up to speed, but once the PTO is engaged the poop hits the fan.  At that moment, the bike will need to supply 20 hp to the system to keep up with the generator or the system will slow down.  If you're applying 1 "human power" to the bike instead of 20 horses worth of power, you can imagine how quickly it will slow down.

It seems the generator is the problem in this equation. So 12v batteries can be charged by an alternator that is easy to move just needs the rpm to generate. I haven't looked at the specs for a low voltage generator but that is an option. I just happened to have the generator so thinking I would use what I have. It seems like the idea of a "flywheel" does work it just needs to be matched. The idea is not to watch tv while I'm peddling but to top off the charge to batteries. I'm also thinking if you need to peddle at top speed for 2 hours straight then I cant physical do it. But if I can peddle top speed for 5 minutes and have a few minutes break while the wheel is coasting then it might be worth building.

I think the only feasible solution is to match the generator to the average power that you can generate for an hour or so. Anything larger will require sprinting and tiring yourself out, and before long you will not have the energy to even coast for a few minutes before the flywheel runs down again. Every time you convert between speeds or directions of motion, you have some conversion losses, so connecting directly from bike wheel to generator would be most efficient. If the generator axle could be continuous with a heavy flywheel you would get more even charging without extra losses, if that is important.

I agree with Glenn. It's not a matter of rpm, it's about how much torque you can produce over a period of time. That determines how much electricity you can generate. Old 14.4-18V cordless drills might be a good place to start. DC motor, with gearing and thrust bearings already in place. Add a handy switch between the drill and the battery, otherwise it will rotate the bike all by itself.

Added: Wire in a cheap analog voltmeter if you can. This will show you when you're generating enough voltage to charge the battery.

Perpetual motion is just about what you are looking at.
Looking at effort to produce the wheel etc compared with some 18V drill batteries I think the plan needs adjustment!

If you can cut back to lights only, you will be amazed at how long your battery will last.
What level of power are you thinking of needing?
How often do you need a back up?

I'm not foolish enough to believe in perpetual motion. I'm not saying I expect a wheel to continue forever after I start it. I know you exhaust more energy in than you get out. I'm just looking for sweat equity up front in order to have a break. The idea is to run a few power tools in a remote shop that has no electric. If solar isn't enough can I jump on the bike get this heavy wheel spinning at X speed that is 10 times faster than the generator needs so I have some time to do something and get back on before power fails. Sometime I would be working after the sun goes down so its either be done until tomorrow or find some way to recharge. Don't have money for more batteries so I'm hoping to use what I have laying around.

Your efforts may have a much better return if you concentrate on powering the tools directly. Pedal or treadle powered table saws lathes etc are out there.

Or just use hand tools?

I think the closest thing to what you are imagining is the Gyro Bus that was designed to enable an electric bus to get through routes where overhead wires were impractical.

Gyro bus? That's a new one on me. Pretty cool at least in concept.

J. O'Chesco wrote:Your efforts may have a much better return if you concentrate on powering the tools directly. Pedal or treadle powered table saws lathes etc are out there.

See also: https://www.notechmagazine.com/?s=pedal+power

The other practical option might be compressed air, which I believe some Amish and related sects use in their shops.

Interesting discussion.

Ancient Romans actually had a rough equation to compare the work output of horses and humans.  As the Romans figured, it took about 10 people to equal the power of one horse.  Granted, that was for pulling things and the Romans didn’t use bicycles.  Also, the modern day HP figure that we use today is roughly 3/4 the power output of what an actual horse could produce (it helped James Watt sell steam engines).  But either way, if one figures 5 persons to 1 HP (a conservative estimate), the 20 HP engine looks pretty far off.

Don’t get me wrong, I like the idea of a flywheel to store energy, I am just thinking that there might be practical limits.  Might a battery bank work?  It could store a charge and be trickle charged with a bicycle generator.  Just a thought.

Good Luck,

Eric

Adam- Stickler wrote:I'm not foolish enough to believe in perpetual motion. I'm not saying I expect a wheel to continue forever after I start it. I know you exhaust more energy in than you get out. I'm just looking for sweat equity up front in order to have a break. The idea is to run a few power tools in a remote shop that has no electric. If solar isn't enough can I jump on the bike get this heavy wheel spinning at X speed that is 10 times faster than the generator needs so I have some time to do something and get back on before power fails. Sometime I would be working after the sun goes down so its either be done until tomorrow or find some way to recharge. Don't have money for more batteries so I'm hoping to use what I have laying around.

What kind of materials do you have at hand to make this generator? I'm not good with numbers, but I'm guessing the flywheel would need to weigh somewhere around a hundred tons to get the usable power out of it you want. Do you have that much material? Is it strong enough material to hold itself together spinning X rpm's at an 8' diameter? Do you already have bearings that can support that much weight? If not, those bearings alone would be quite expensive (more than batteries or solar panels, I imagine). You said you want to gear it directly to a gear on the outside of the wheel...Do you have this gear or the means to make it? What kind of lubrication system do you have to use on such an arrangement? The generator will have to spin at a constant speed, so how will you alter the speed of the wheel to constantly keep the generator turning at 540rpm? Do you already have such a transmission? If not, I imagine one would cost many thousand dollars. There would also likely need to be a special transmission between the bike and the wheel as it would need to be geared down greatly to spin such a mass from a standstill, then geared up to get the wheel up to full speed.

It's difficult to tell without having actual numbers to plug into the equations.

Based on prior comments I have scrapped the idea of running a pto style generator. I'm not sure what low voltage generators would need to run. Either way this sounds like it's a waist of time to build. I was going to build the wheel from wood and spare hardware. I like to keep things simple and effective so lets take this in a different direction. I have read some claims that a solar tracking array can improve charge. This sounds legit and part of the problem is I'm not getting the batteries completely charged in one days charge. Does anyone have any real life experience with these solar trackers?

Trackers generate more electricity than their stationary counterparts due to increased direct exposure to solar rays.
This increase can be as much as 10 to 25% depending on the geographic location of the tracking system.
They can be automatic or manually changed.
The auto  ones track the sun everyday, the manual one are set to a better general direction each week for instance.

Either system is costly if you purchase something.

Here is an article about them solar trackers
The page / web site has a newsletter you can subscribe to for more solar info over time.

Adam,

A solar array sounds like a practical idea.  Do you have solar panels right now?  If so, how many and what is the peak output per panel?  This is just to get an idea of where we are starting.  Also, what orientation are the panels facing?  Do they face straight up at the sky?  I have a small solar backup power setup and it is charged with a single solar panel.  When I charge, I always orient the panel facing south, especially in the winter.

On the other side of the equation, how many batteries are you charging and what size are they (in amp/hours).  I assume they are 12v batteries?

Solar is a cool idea.  It has its own tricks and limitations, but it can certainly be done.  I would love to hear what you are working with at present.

Eric

Interesting.... heh, this is the second time in a few days that I have come across those images of the "gyro bus" - I had been doing some research related to mechanical energy storage (I could use more batteries in my solar powered system as we can go days without much sun input, and then quickly will have more energy than we can use).

It seemed to me that mechanical energy storage in terms of flywheels may have industrial/grid scale uses, but it isn't really practical for residential and small scale systems. I know that the OP isn't looking to store energy in a flywheel per se, but given that the efficiency of a particular generator will require an input of energy sufficient to hit the target RPM....

So, I wonder if the bicycle could be used to run a water pump to lift water to a raised storage tank/area. The bicycle could operate at any speed and the user could pedal whenever they feel they have the time and physical energy to do so. Then, the water could be released in a controlled manner to run a Pelton wheel and generator. It wouldn't need to be a very expensive or complicated system.

The amounts of power generated may be small, but perhaps this is a direction to look into...?

Additionally, the system could collect and store precipitation at that height (raised water collection, in the canopy of forest etc.)

It would seem to me that the main issue identified with the starting idea of the pedal driven hamster wheel is the ability to keep sustained power. If the bicyclye water pump potential energy/Pelton wheel idea isn't appealing, or is too complicated, the giant geared hamster wheel could be run with anything that could be carried to the top of it, and then pulled back down via gravity... I am imagining the user (with a great expenditure of physical energy) lifting bags of sand up onto a platform, and then once the platform is full, climbing up, and spending 5-10 minutes driving the wheel by dropping the bags of sand onto it, like a traditional water wheel in a stream/river... in this way the wheel could be powered for some time...