Bike powered electricity generators are not sustainable

Pedalling a modern stationary bicycle to produce electricity might be a great work-out, but in many cases, it is not sustainable. While humans are rather inefficient engines converting food into work, this is not the problem we want to address here; people have to move in order to stay healthy, so we might as well use that energy to operate machinery. The trouble is that the present approach to pedal power results in highly inefficient machines.

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When operating a bicycle generator you are basically pedalling to produce the energy required to manufacture the battery.

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There are two ways to power a device by pedalling. You can power it directly through a mechanical connection - as was the case with all pedal powered machines for sale at the turn of the 20th century. Or, you can pedal to generate electricity, which is then used to power the device. In the 1970s, most research was aimed at direct mechanical power transmission. Today, the interest in pedal powered machines is almost exclusively aimed at generating electricity, for instance for charging cell phones and laptops - products that did not even exist in the 1970s.

With one exception (the 'Fender Blender', a pedalled powered machine to make smoothies), the only pedal powered machinery that is now commercially available in the western world (offered by Windstream, Convergence Tech and Magnificent Revolution) are stands to fit your bike to, connected to an electric motor/generator and a battery - a combination that can quickly convert your regular road bicycle into an electricity generator. These are also the pedal powered machines which are used for educational and arts projects, like powering a music concert, a cinema projection or a supercomputer, or teaching kids the difference in energy use between, for instance, an incandescent light bulb and an energy saving lamp.

In an effort to raise awareness about energy use and global warming, the BBC even made a TV-programme in which an entire household was powered via these generators, with 80 cyclists generating up to 14 kW. These multi-person pedal power generators were pioneered in the 1970s by the Campus Center for Appropriate Technology (CCAT).

Generating electricity is very inefficient

There are several problems with the present-day approach to pedal power. First of all, it is important to know that generating electricity is far from the most efficient way to apply pedal power, due to the internal energy losses in the battery, the battery management system, other electronic parts, and the motor/generator.

These energy losses add up quickly: 10 to 35 percent in the battery, 10 to 20 percent in the motor/generator and 5 to 15 percent in the converter (which converts direct current to alternate current). (Sources: 1/2/3). The energy loss in the voltage regulator (or DC to DC converter, which prevents you from blowing up the battery) is about 25 percent (sources: 1/2).

This means that the total energy loss in a pedal powered generator will be 42 to 67.5 percent (calculation example for highest loss: 100 watt input = 80 watt after 20% loss in motor/generator = 57.5 watts after 25% energy loss in voltage regulator = 37.5 watts after 35% loss in battery = 32.5 watts after 15% loss in converter = 32.5 watts output = efficiency of 32.5% or energy loss of 67.5%).

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You have to pedal 2 to 3 times as hard or as long if you choose to power a device via electricity compared to powering the same device mechanically

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Furthermore, there will be an additional slight loss as the battery stands idle, and the charge efficiency (also known as "charge acceptance" or "coulombic efficiency") of the battery will deteriorate over time. And to make the calculation complete, you should actually also include the energy loss in the electrical device that you are powering (we won't do that here).

An energy loss of 42 to 67.5 percent of naturally means that it takes 42 to 67.5 percent more effort or time to power a device (say, a blender) via electricity compared to powering the same device mechanically. This can be considered an acceptable loss if you are using solar panels or a wind turbine connected to a battery as an energy source, but it becomes rather problematic when you have to deliver the energy yourself.

If you produce 100 watts of power and 42 to 67.5 percent is lost in the conversion, there is only 32.5 to 58 watts left to power the device. If you power the same device mechanically, you deliver 100 watts straight to it. You thus have to pedal 2 to 3 times as hard or as long if you choose to take the intermediate step of generating electricity and storing it in a battery.

Traditional bicycles were not made to generate stationary power

It does not stop here. The second problem with the present approach to pedal power is that it uses a traditional bicycle on a training stand instead of a pedal powered machine built from scratch - as was the case at the end of the 19th century. Of course, using a traditional bicycle has its advantages, but again it should be realized that this approach is considerably less efficient.

One reason is the use of a so-called friction drive - the rear bicycle wheel acts upon the small roller of the motor/generator. While chain and belt drives (used in late 19th century pedal powered machines) have an efficiency of up to 98 percent, a friction drive is only 80 to 90 percent efficient (and wears much faster). This energy loss should be added to the 42 to 67.5 percent efficiency loss calculated above, which rises to 48 to 73.5 percent. Low tyre pressure will further decrease efficiency.

It should be noted that there is also energy loss in the bicycle itself: your pedals are not attached to the rear wheel itself. You turn a sprocket, which turns a chain, which turns a sprocket, which turns the rear wheel. So, on top of the efficiency loss of the friction drive should be added the efficiency loss of a chain drive (plus the energy loss in the derailleur, if your bike has one).

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Additional energy losses occur when using a racing bike or a mountain bike

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Connecting a bike chain directly to the generator would prevent the energy loss of the friction drive, but it implies that you have to adapt the bicycle - destroying the whole concept of today's commercially available pedal generators.

Racing bicycles

Additional energy losses can occur when using a road bicycle to generate electricity. For example, the picture accompanying the Windstream generator shows a racing bicycle. This is a very bad choice, because the position of a rider on a racing bike is aimed to reduce wind resistance. Tests on ergometers (stationary bikes used to measure the power output of cyclists) have shown that pedalling in such a position is only about 80 percent as effective compared to a normal upright position, again resulting in considerable energy loss.

On the road the rider position on a racing bicycle is beneficial because of the large importance of air resistance. However, on a stationary pedalling machine this position has no advantage whatsoever. The popular mountain bike is equally disadvantageous because of the corrugated tyres, which of course lower the efficiency of the friction drive. In short, while using a road bicycle to generate electricity has the advantage that you can use your own bike, this does not mean you can use just any bike.

Flywheel

Another important drawback of using a common road bicycle is the absence of a flywheel - a heavy disc made of concrete, wood or steel that continues to generate power after it has been put in motion. In a pedal powered machine built from scratch, like the ones used at the turn of the 20th century, the flywheel applies the function of the rear bicycle wheel in the training stand (although the flywheel is mostly placed at the front of the machine). The pedaller powers the flywheel, and the flywheel powers the machine (which can be a mechanical device or a motor/generator to produce electricity). 

Why is a flywheel advantageous? Because there is an important difference between riding a bicycle on the road and pedalling a stationary machine. If we are pedalling, the power exerted by our feet on the pedals is inconsistent. It peaks every 180 degrees of crank rotation, and because the two cranks are placed 180 degrees out of phase this results in two power peaks per turn of the crank. Similarly, there are dead spots in between at the top and bottom position of the pedals (to be correct this minimum torque is not zero but about one third of the maximum).

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On a stationary bicycle without a flywheel, the natural pedalling rhythm results in jerky motion, limiting the energy output of the rider

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On a bicycle, this uneven exertion has little effect because of the inertia of both bike and rider. But on a stationary pedal powered machine, this natural pedalling rhythm results in jerky motion and additional stress on parts.

Because of its large mass and rotational speed, the flywheel evens out the difference between power peaks and dead spots. Evening out the power input means that the rider tires less quickly and can thus generate more power. The obvious disadvantage of a flywheel is that it is heavy - from 10 to 80 kg for stationary pedal powered machines - and thus not exactly mobile.

Generating electricity is not eco-friendly

Generating electricity is not only ineffiicient, it also makes pedal power less sustainable, less robust and more costly. To begin with, batteries have to be manufactured, and they have to be replaced regularly. This requires energy, which can completely negate the ecological advantage of pedal power.

According to this research paper (pdf), the embodied energy of a 150Wh lead-acid battery (like the one offered with the Windstream pedal power generator) is at least 37,500 Wh, which equals 250 full charges of the battery (more sources: 1/2). In other words: if you can deliver 75 watts of power to the battery, you have to pedal for 500 hours in order to generate the energy that was needed to manufacture the battery. Because the life expectancy of a lead-acid battery can be as low as 300 discharge/charge cycles (sources: 1/2), you are basically pedalling to produce the energy required to manufacture the battery. If you also factor in the embodied energy of other electronics and parts, the ecological advantage of a pedal powered generator connected to a battery becomes rather doubtful. It might costs more energy than it delivers.

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A pedal powered generator might cost more energy than it delivers

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Of course, it also takes energy to manufacture a pedal powered machine that does not take the intermediate step of generating electricity. This concern lies mainly with the production of steel, and quite a lot of it. The commercially available Fender Blender mentioned earlier weighs 25kg (55 pounds).

If made from recycled steel, and using these figures to calculate the embodied energy of steel, this comes down to an energy cost of at least 41,625 Wh, slightly more than the battery needed for the electricity generator. If freshly made steel is used, the embodied energy is at least 138,750 Wh (3.7 times the embodied energy of a single battery). However, these machines can last at least 100 years (pedal powered machines surviving from the late 19th century are still in use), while the battery of the electricity generator has to be replaced every few years.

If we ignore the embodied energy of other parts than the battery (both training stand and electronics), and take a life expectancy of 4 years for the battery (rather optimistic), a pedalled powered generator would require an embodied energy of 937,500 Wh over the course of 100 years - 6.7 to 22.5 more than a mechanical unit. Moreover, it is easy to make the frame for a mechanical pedal powered machine from scavenged materials, bringing the embodied energy down to almost zero, while this is an impossibility for the batteries. Never mind that in addition, the toxicity of the materials is another thing to consider.

Generating electricity is less robust and more expensive

While a pedal powered machine is the most robust and resilient energy source around if you power devices mechanically, this advantage is lost when you start generating electricity. Few people can manufacture batteries themselves, so you remain dependent on a regular supply of replacement batteries.

Furthermore, the electronic parts of the machine (voltage regulator, motor/generator, converter) can break down and are not easy to make or repair yourself either - contrary to old-fashioned pedal powered machines, which can be fixed yourself with readily available materials. Mechanical pedal powered machines are generally even easier to repair and maintain than bicycles.

The extra components also make pedal generators more expensive. The commercially available models sell for $700 to more than $1000, not including the necessary replacements of the battery over time. Even if you make your own pedal power generator, the costs add up. The 2008 book 'The Human-Powered Home: Choosing Muscles Over Motors', which has plans for several kinds of pedal powered machines, estimates the costs of a DIY generator at about $50 (using scavenged parts) to $350 (using new parts), not including a bicycle stand and replacement batteries. Another source estimates the cost at $600.

The mechanical pedal powered machines in the book can be built for $10 to $50 (the washing machine being more expensive at $100), everything included. While the only commercially available mechanical pedal powered machine today is very expensive too (the Fender Blender sells for $1,700), the high cost is almost entirely due to the steel frame - which, as mentioned, could easily be replaced by the frame of an old exercise bike, or built oneself from scavenged materials. Moreover, there are no additional costs for replacement batteries and the machine is built to last for a very long time.

Continue reading: How to make pedal power efficient and sustainable?

One way to solve the large energy losses of pedal power generators is not to produce electricity at all and power devices mechanically, whenever possible. Another way - the only way for devices that cannot be powered via a direct mechanical connection because they do not rely on rotary motion - is to make the generation of electricity more efficient.

This can be done by building a pedal powered generator from scratch instead of using a road bicycle, and/or by ditching one or several electronic components in the power transmission chain. All approaches can be combined, resulting in a pedal power unit that can power a multitude of mechanical devices and generate electricity comparatively efficiently. Read more.

Kris De Decker (edited by Shameez Joubert)

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Sources (in order of importance)

• "Pedal Power in Work, Leisure and Transportation", edited by James McCullagh, Rodale Press, 1977. Still the best resource on pedal powered machines.
• "The Human-Powered Home: Choosing Muscles Over Motors", Tamara Dean, New Society Publishers, 2008. Very good book on human powered machines, both hand and foot powered. Includes half a dozen plans to convert bicycles into stationary pedal powered machines.
• "Bicycling Science", Third Edition, David Gordon Wilson, 2004
• "The Dynapod: a pedal power unit" (pdf), Alex Weir, 1980. More here.
• "The use of pedal power for agriculture and transport in developing countries" (pdf), David Weightman, Lanchester Polytechnic, 1976
• "Design of a human-powered utility vehicle for developing communities", Timothy J. Cyders, 2008
• "Supplement, Energy for rural development", National Research Council, 1981
• "Tales from the Blue Ox ", Dan Brett, 2003
• "Bicycles and tricycles", Archibald Sharp, 1896
• "In search of the massless flywheel" (pdf), John S. Allen, Human Power (Fall/Winter 1991-1992)
• "Design and development of a human-powered machine for the manufacture of lime-flyash-sand bricks", J.P.Modak & S.D.Moghe, Human Power (Spring 1998)
• "Human Powered Flywheel Motor: concept, design, dynamics and applications", J.P.Modak, 2007
• "Modern mechanism: exhibiting the latest progress in machines, motors, and the transmission of power", Benjamin Park, 1892
• "Make electricity while you exercise", Mother Earth News, 2008
• "Luther's tool grinders" (pdf, 5.8 MB), hand and foot powered grinders catalog. Hosted at Toolemera Blog.
• "Woodworkers' tools and machines" (pdf, 29 MB), product catalogue no.25, 1884, Richard Melhuish Ltd., Tool and Machine Merchants, London. Hosted at Toolemera Blog.
• "Science & civilisation in China, Vol.5, Part 9", Joseph Needham, 1988

Related articles:

• Hand powered drilling tools and machines
• Human powered cranes and lifting devices: the sky is the limit
• Wind powered factories: the history and future of industrial windmills
• The bright future of solar powered factories: we need a renewable source of heat energy
• The velomobile: high-tech bike or low-tech car?
• Cars, out of the way: what you mean, bike lanes?
• The industrialization of traffic: why bicycles are faster than cars
• Computing without electricity: mechanical calculators
• The museum of old techniques
• Wind up your laptop
• Automata: engineering for a post-oil world?
• Life before television
• Short posts on pedal power can be found at No Tech Magazine
• Full plans for a pedal powered juice extractor

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Comments

[Mr. S.]

(1)

As for energy storage, wouldn't making the pedal-powered machine actuate a vertical water-pump be ideal? No electronics, or chemical battery, and when power is needed water can be released from a water tower to generate current with some kind of turbine. Better yet, a windmill could be the primary power for the pump, with pedal power as a fallback for long windless periods.

[Kris De Decker]

(2)

Sounds like an interesting concept to me. But, the question is how big that tower has to be, and how much energy it takes to build it.

[charley hardman]

(3)

love this article. have long been fascinated by human power, and would like to live in a human-powered home. my vague design centers on several transmission methods (e.g., bicycle, fitness machines), all connected to a lifting a large weight that may be lowered on demand for electricity or straight mechanical power. similar to Mr. S's description with water (as used regularly for time-shifting hydroelectric power).

of course, a unilateral human-powered home requires radical changes in HVAC, mostly centering on acclimation and localization (e.g., electric clothes).

[Andy]

(4)

I had plans drawn out for a while now around the concept Mr. S explains. Many well designed off grid homes use elevated water so that they still have running water available, but they rely on using a generator once in a while to push the water. I always thought a small windmill could do the work of lifting the water into a small tank, and when electricity is desired, then this essentially turns into a microhydro system as water empties from the tank while spinning a series of turbines as it falls.

Kris, it's nearly pointless to question the energy required to build this type of system. It's obviously considerably less energy both upfront and continuing versus being grid tied (relying on miles of copper) and coal/nuclear/gas providing that power.

[Colin Tonks]

(5)

Hi Kris, this is an interesting piece of work and well put together. I especially enjoyed reading the history of the pedal powered machines.

Furthermore, I absolutely agree with you that humans generating energy, with a bicycle, is completely inefficient. In fact, the cost of the food required to pedal would be 150 times more expensive than the cost of buying the energy direct from a local supplier. So what is the point and why do we do this?

Well, there is one important point that I would like to make and that is the indirect benefits of this approach when applied in an educational environment. We’ve done hundreds of events using the technique of people generating their own electrical energy and then using it to do something fun. It does not matter if it's a festival, school, corporate etc., we get the same reaction every time .. a new found appreciation for energy.

For many people, pedalling to boil a kettle of water or even lighting a light bulb is ‘enlightening’, it's that relationship between what they are feeling in their body, the burning their muscles, the excitement of being in control to bring alive an electrical appliance that is stimulating and thought provoking.

I'm not saying that people who generate their our energy go away and become eco warrior and start wear heap shoes, it's more of a subtle push in the right direction, a small step change in behaviour that would hopefully lead to a more sustainable existence. Thanks Colin

[Kris De Decker]

(6)

@ Andy: I am interested to know more about the plans you drew out. Some time ago a reader asked if there existed something like 'micro hydro pumped storage' because he wanted to be fully energy independent without using a battery. He had asked an architect to design such a system but the architect just laughed and walked away.

So I made a calculation myself and concluded that you need quite some spectacular reservoir if you want to have a pumped storage for your house, even if you use considerably less energy than the average household. (I lost the calculations, unfortunately). I guess it's not only a matter of embodied energy (a water tower can last for decades, so indeed this might not be such a problem), but also of space. It would be great to hear more ideas on this topic.

@ Colin: I support what you are doing and I am convinced that your projects do have a positive effect on people's behaviour. And if I got it right, you did not use batteries for the BBC TV series? I think it's obvious that I am a supporter of pedal powered energy, including generating electricity for devices that can't be driven mechanically, but we have to find a way to do away with the batteries, because they destroy the whole concept from an ecological/efficiency viewpoint.

[charley hardman]

(7)

i approach the efficiency topic from the other side. i loathe "working out", lifting weights only to lower them. would like that converted into useful power along with the physical benefit. any true analysis must include wasteful expenditure of the subject that might be converted. caloric analysis must at least also subtract normal spending for mere existence (e.g., sitting in a chair reading book).

i suspect the most practical local solution is hydraulic power transmission (i.e., high pressure, little movement) to a dense mass (e.g., lead). don't think water will cut it as per-home kinetic energy storage medium.

[Chris Vernon]

(8)

I've tinkered with bicycle electricity generation, thanks for this fascinating article.

Regarding the 10 to 35 percent lose in the battery and 5 to 15 percent loss in the DC/AC converter, for many applications an ultra-capacitor can be used to maintain/smooth the voltage and of course we should only be using DC loads! No point it going anywhere near AC. These two points improve the efficiency quite a bit, but fundamentally, I agree with your conclusions we should be powering devices mechanically.

[Adrian]

(9)

A brilliant article, as they always are, but...

You say "An energy loss of 42 to 67.5 percent of naturally means that it takes 42 to 67.5 percent more effort"

Wrong maths! Say you had a 90% loss, you'd need to provide 10 times as much energy to get the same result. Or 900% more.

So a 67.5% loss means 100/(100-67.5)*100 = 3.07 times as much input energy is required, or 307% as the original, or 207% extra input energy.

[Mike]

(10)

I've been playing with the idea of using a bike and alternator to power an electric water heater. The electronics aren't necessary then and alternators can come from junkyards for $35 or so. An RV 12-volt heating element costs less than $100. Any old water heater should work.

Of course, I don't have a working prototype running yet. But I'm fairly close and the process hasn't been particularly difficult so far.

[Michael Dawson]

(11)

Has anybody applied this kind of analysis to the so-called electric car? Where could one find that?

[Kris De Decker]

(12)

@ Adrian (#9): You must be right. I will correct it. Math is such a weird thing: I made a mistake in the calculations but the end result was correct...

@ Mike (#10): Interesting idea. Generating electricity to produce heat is considered to be very inefficient, but using the water as a battery at least makes the whole system sustainable. I think the only downside is that you will have to pedal a lot to take a hot shower.

[Kris De Decker]

(13)

@ Michael (#11): I made a calculation of the embodied energy of an electric car battery here (about halfway the article):
http://www.lowtechmagazine.com/2010/05/the-status-quo-of-electric-cars-better-batteries-same-range.html

It was a rough calculation because of the few sources available, and meanwhile another study appeared which arrived to figures which are about half as low: http://pubs.acs.org/doi/full/10.1021/es903729a

It should be noted that this research paper was sponsored by a Swiss electricity producer and a lithium mining company (see the last paragraph). I guess we would be somewhat suspicious when a research paper sponsored by the oil industry concluded that gasoline powered cars are better for the environment than electric cars... Anyways, the embodied energy of batteries definitely makes electric cars less sustainable than is generally assumed.

And what about solar panels + battery? One of the sources I refer to concerning the embodied energy of a battery, talks about solar panels connected to batteries in an off-grid system. From their numbers it can be concluded that in less sunny regions the energy payback time is longer than the life expectancy of the solar panels. Without batteries, energy payback time is positive. See the discussion here: http://www.lowtechmagazine.com/2008/03/the-ugly-side-o.html?cid=6a00e0099229e888330120a69d6a05970c#comment-6a00e0099229e888330120a69d6a05970c

[jason crowther]

(14)

in order to re-gain the strength i lost due to head-injury, i spent much time on a rowing egometer. the appartus included a monitor measuring various outputs during a workout. eventually, i reached 46,400 watts/41 minutes. of course, these measurerments increased as my strength and endurance increased. i remember thinking that--maybe--i was onto something! could i use this system to increase my income through selling the power back to a local provider?

[jshill]

(15)

The assertion that "An energy loss of 42 to 67.5 percent of naturally means that it takes 42 to 67.5 percent more effort or time to power a device (say, a blender) via electricity compared to powering the same device mechanically" has a math error. The numbers to use are 1/(1-.42) at the low end and 1/(1-.675) at the high end. So you'd actually need 1.724 to 3.077 times more energy to compensate for a lost off between 42 to 67.5 percent.

[esqua]

(16)

To the author: I am a cyclist and I need to train indoors occasionally. I am thinking of finding a used DC generator and AC converter to run with my road bike. I understand that there is quite a bit of energy loss, if I try to store it. But could I just plug the AC current into my wall socket to slow or run my meter backward? I need to do the work out anyway, might as well do something with the energy.
Your response would be appreciated.
Cheers!

[Michael Boswell]

(17)

The advantage of simple pedal power is that almost all humans have legs and can generate power small machines. The best Australian example is the pedal wireless. This simple invention provided communications to regions of Australian were electricity supplies were non-existant. Which prior to World War 2, was most of the Australian land mass. Naturally, this two way radio service was public but no one ever listen to another conversation. Well, not much!

The other useful thing for human power machines is for things like sowing machines. I have heard many old ladies bemaon the disappearance of the old 'pedal sowing machines". One control was the amount of power that you put into the machine. Electric ones have other means to vary power but one cannot feel the power going into it.

This is my first time here and I am subscribing.

[Rolf]

(18)

I am interested in the use of pedal power while people are driving to generate electricity; though ineffecient, if a person is idle and not able to use time more efficiently any other way, this is a use of energy that otherwise cannot be used otherwise. Use of pedal power to charge batteries for use of power either in vehicle or for other purposes - and get needed exercise for our sedentary culture.

[Matthew]

(19)

I've been intrigued by this "people power" concept for a few years. I don't have any technical knowledge of how this works. It seems to me there should be some way to use human activity to generate power or to power devices in some way. There are some indirect benefits in the form of more exercise, particularly for combating obesity including childhood obesity. If there's a people-powered device in every home, perhaps families could generate enough electricity to watch TV or charge their cellphones, etc. Parents could make sure their kids participate in generating enough power for the family to watch a program or play a video game. It could be a trade off: Sure you can play that video game, but you need to do some pedaling to make it happen! That kind of thing. It may not be efficient energy production but it has side benefits. Another application would be for emergencies, say when a hurricane knocks out power to your house. A bicycle-powered device could help pump out excess water from the basement, sound an alarm, provide lighting, or charge cellphones for emergency phone calls, etc. All things considered, it would seem that this concept has some potential, especially if you consider that millions of people drive to a fitness center (using energy to manufacture and power the car) and then turn on various electricity-driven exercise devices (like treadmills). Why not encourage energy production and/or create practical devices that are driven by human exercise in homes or at green fitness centers? There may be efficiency breakthroughs the more scientists and engineers explore how best to generate and harness energy produced by "people power."

[Tom]

(20)

If you make an electricity generating device (I built a rowing machine) from scrap materials (- I got a usable battery from the scrapyard also) then the energy that has been put into making those parts is history you can't change that but by using those parts to make electricity at least you are recouping some of it and balancing things in a positive direction overall

[jane hansen]

(21)

I am looking for the best way to use "human power" to run a sump pump in the event of a prolonged power outage. I had thought to use a bicycle to charge the back up battery...but may be there is a better way. Got ideas anyone???

Jane H.
Barrington, IL

[Brian Hansen]

(22)

Jane (#21): I think one message from this article is that using direct rotational energy is hard to beat for efficiency. From an engineering perspective this may be a principle in search of an application. When I think of a sump pump, I think of it as being asynchronous, running only when needed, for as long as needed. That scenario would suggest stored energy to run the pump.

It is possible, though, that it could be routinized, or perhaps scheduled, such that an individual could "ride" for 10 minutes every 6 hours, for instance. Or "ride" as long as needed when an alarm went off.

A direct mechanical linkage would present its own problems, of course. The bike has to be next to the pump.

[Kris De Decker]

(23)

@ Brian: "The bike has to be next to the pump."

Unless you use a jerker line system: http://www.lowtechmagazine.com/2013/02/the-mechanical-transmission-of-power-jerker-line-systems.html