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pedal power
By stop4stuff, Section Homebrewed Electricity Posted on Tue Aug 10, 2004 at 07:49:07 AM MST
converting an exercise bike

Hi All,
I went to the shop and I bought...
An exercise bike, with computer :)

(Netto, Fitness R2000 Exercise Bike, £39.99)
And then I investigated it's workings...

The 'effort control' is a felt type band around a 160mm (~6.3") diameter, 26mm (~1") wide brake drum :)
With the band and control moved out of the way, there's a minimum of 20mm clearance from the drum to the frame...
...and a 1"(l) x 1/4"(w) x 1/4"(h) neo magnet (highlighted) fits nicely on the outer edge.

Perfect for an axial alternator... maybe...
Here's an image (to scale) of what I think may work (the coils have a laminate 'lug' in the middle)

There's 36 magnets on the rotor and a single phase of 18 coils in a laminated stator... space may allow for 36 coils, 2 phases of 18 coils each.
My questions...
With so many magnets and coils, as single phase, would cogging be a problem?
Will steel car panels be ok for the laminate?
I'd be aiming for a max of 250w (15-17v) at around 100 rpm, or 12v+ at around 70 rpm (for the wifey ;)...
...any suggestions for the wire size, or total resistance of the coils?
cheers,
paul

pedal power | 14 comments (14 topical)

Re: pedal power (3.00 / 0) (#1)
by Flux on Tue Aug 10, 2004 at 08:36:15 AM MST

I think the drum is too small to get 250W at 100 rpm, you would need an enormous amount of magnet material.
As shown it will cog badly, but I can't see that being a problem with pedal power.
It would be better with the same number of polar projections on the stator as magnets.

Car body steel is very poor, but it depends on the amount of electrical power to exercise you are aiming for, the added drag would keep you fit.

I should consider using the drum as part of a belt drive step up to a faster alternator. V poly-V and timing belts will all work on a large smooth pulley.

Flux

Re: pedal power (3.00 / 0) (#2)
by whatsnext on Tue Aug 10, 2004 at 08:51:18 AM MST

I have a 'Lifecycle' brand exersise bike I use in the winter months. Main reason for that is because the drum gets so damn hot it overheats the room. It's just a PM generator with the coils shorted. Resistance is varied by means of a stepper motor that moves the PM assy in and out of the drum. The head unit claims that the load maxxes out at 2000cal/hour which is VERY difficult to sustain for any length of time. Between me and the bike, we have no problem heating up the room and the drum get's hot enough that it keeps you from touching it even though it's constantly spinning in the air.
John...........

[ Parent ]

drum=heated hot water (3.00 / 0) (#3)
by Norm on Tue Aug 10, 2004 at 11:47:17 AM MST

What a neat way to heat water for a coffemaker...by the time the coffee was done...you would be also!
( :>) Norm.
( :>) Norm
[ Parent ]

Re: pedal power (3.00 / 0) (#4)
by troy on Tue Aug 10, 2004 at 12:52:28 PM MST

Exercise bikes that actually do something useful are a hoot. I converted a chain drive model to drive a radial pm alternator. Here are a few first hand observations:

If you can make more than 100 watts for 30 minutes, you are a heroic cyclist. I've done a lot of cycling, including several centuries (over a hundred miles in a day) and my pretty good workout is 5.5 amps x 13.5 volts = 74 watts for 30 min.

Here's a pic of my machine:

I am also highly doubtful you will get the output you want at a "normal" cadence (less than 100 rpm) unless you install some monster magnets with some monster coils. My dual rotor alternator had to be geared up more than 3:1 to get enough rpms for a decent output. ymmv

Good luck and have fun!!

troy

Re: pedal power (3.00 / 0) (#5)
by TomW on Tue Aug 10, 2004 at 01:19:07 PM MST

troy;

This is a good example of just how much power a "few" watts takes to generate. Flipping that switch for that 100 watt bulb will take on new significance if you are pedaling the power source when it happens.

I think most folks are pretty unaware of just how much power things actually take to operate. After all we just flip a switch and it flows [usually].

Cheers.

TomW

The Truth is the Truth, even if no one believes it; and a lie is a lie even if everyone believes it

[ Parent ]

Re: pedal power (3.00 / 0) (#6)
by stop4stuff on Tue Aug 10, 2004 at 03:36:00 PM MST

Thank you all for the input.

Flux,
here's a piccy of the stator without the coils, 36 polar projections (lugs)

What sort of magnet power should i be looking for?

(respectfully) TomW,
I understand what it takes to make a Watt. My current Lego alt easily puts out 3.5W, hand cranked on a 1.25" crank (finger and thumb stuff :)... the 'Raxial alt' is coming on nicely... the flux coming off the opposing magnets 'seems' to have increased over time (4" rotor, 12 poles, 2 coils, 4v A/C (open), 2A A/C (short) @ 900rpm... another story ;)

Troy,
I like your setup, how many magnets and coils (+wire size :) did you use?

I'm less fit than I used to be, however I used to top 500 miles per week on a bicycle. I'd basically do 30-50 miles in the morning, the same in the evening (weekdays) and 150 - 250 miles over the weekend. I once got stopped by the police for going 56mph in a 40 area :(

Google for the 'Gossamer Albertross', a pedal powered carbon fibre aircraft that crossed the English Channel (22 miles 453 yards) in 1979. The 'rider' had to sustain 1/3 hp to acheive the 2hr 49min flight.

When I tried out the exercise bike, I could sustain 100 rpm for 15mins on a high setting and peaked 130 rpm... hard work tho... gonna get fit again :)

Oh... some info about human body heat output...
http://ergo.human.cornell.edu/studentdownloads/DEA350notes/Thermal/thcondnotes.html

Where did I put those the glucose tablets...
paul

afterthought::: could the heat generated by a nightclub full of dancing drunks be distributed to the needy in winter?

Re: pedal power (3.00 / 0) (#7)
by Flux on Tue Aug 10, 2004 at 04:15:31 PM MST

Paul
Sorry I didn't realise the teeth were in the coils, although when I read your post again you did say so.
I think you may have a problem with the 20mm clearance to get enough magnet and have a reasonable iron circuit if you want good efficiency.
If you went up to 60 magnets you might have some chance or perhaps use 36 wider ones.
There doesn't seem room for anything thicker. you will need a lot of turns with a lot of resistance and you may run into a problem with reactance.

Do you intend to use the AC or rectify it to charge a battery ?
Flux

[ Parent ]

Re: pedal power (3.00 / 0) (#9)
by stop4stuff on Wed Aug 11, 2004 at 02:39:51 PM MST

no probs Flux,
The alt would be used rectified to charge a battery, with an inverter hooked up to run 240v AC (UK mains) appliances...
After some thinking, an ordinary bicycle complete with gears and rear wheel, with loads of magnets around the rim of the wheel may yield more power.

paul

[ Parent ]

Re: pedal power (3.00 / 0) (#10)
by Flux on Wed Aug 11, 2004 at 03:30:24 PM MST

That seems a much better idea, bicycle gearing is quite efficient.
Also for battery charging single phase is not very good, you will have a much better chance of going multiphase with lots of room to spare. The gears will also let you change load without having to alter turns or magnet clearance.

Perhaps a small wheel from a child's bike would reduce windage and may be a simpler mechanical solution. Good luck

Flux

[ Parent ]

Re: pedal power (3.00 / 0) (#8)
by hvirtane on Wed Aug 11, 2004 at 12:06:03 PM MST

We just made a pedal generator using
an exercise bike and a washing machine
permanent magnet motor as the generator.
We are using a belt drive.

Some power tools like a drill,
an angle grinder etc are working
well with the machine.

I'm just trying to convert
a coffee maker to be used
by pedaling.

According to various studies
a normal fit person can
produce something like 150 watts
continuously. But it isn't
so easy to make a pedal power
machine efficient...

I will post some pictures after
the coffee machine
will start working.

- Hannu

Re: pedal power (3.00 / 0) (#11)
by Ungrounded Lightning Rod on Wed Aug 11, 2004 at 08:02:10 PM MST

According to various studies a normal fit person can produce something like 150 watts continuously.

Pedal in shorts and use a small fan to get some airflow past your legs. Then you'll be able to put out a lot more power for a longer time. (Some stationary bikes have a little centrifugal blower powered mechanically from the bike itself. Convenient.)

The main limit on how much power you can put out is how well you can cool your legs. This is why cross-country bicycling burns a lot more fat than you can on a stationary bike without a fan attachment.

Humans are designed to jog for hours at a time - apparently they were corsorial hunters at some point - running down fur-covered animals by jogging after them until they collapsed from heat prostration. That's why we lost most of our hair - except where it lubricates rub points or provides insulation for the brain or color patches for signaling - and sweat all over: Losing heat to run longer without overheating. Also the upright gait and the structure of the springy pads between the bones (recycling energy from one step to the next) helps us run efficiently. A person in good shape can run down deer, antelope, and horses without too much trouble. (Donkeys are more problematic.) Get your power takeoff on the bike correct and provide enough cooling and you can drive it for hours.

If you're really into optimizing such a device you might also want to look into using a chain drive with an eliptical pedal chain sprocket that adjusts the load at various leg positions to match the legs' output, ala nautilus exercise equipment.

[ Parent ]

Re: pedal power (3.00 / 0) (#12)
by Jerry on Wed Aug 11, 2004 at 09:59:58 PM MST

Best I can pedle out of this one is 150 watts. Odly enough that beets my 12 year old grandson.

This one is doing about 140 volts ac into a 120 volt bulb. Its also fun to run drills ands saws and such. Small TV works good to but i run out of steam befor the shows over.

JK TAS Jerry

Airheads Page

[ Parent ]

Re: pedal power (3.00 / 0) (#13)
by Jerry on Wed Aug 11, 2004 at 10:03:55 PM MST

PS its belt drive from the 14" flywhell down to the 6" pully on the converted 6 pole ac motor.

JK TAS Jerry

Airheads Page

[ Parent ]

Re: pedal power (3.00 / 0) (#14)
by hvirtane on Thu Aug 12, 2004 at 10:46:01 AM MST

Hello Jerry,

it is really funny that your bike
in the picture is
exactly the same as ours!

It is 'Tunturi' made in Turku, Finland.

It is funny that such things are exported
from Finland to the other side of the
Atlantic ocean.

Have you tried to run a coffee maker
with it?

- Hannu

[ Parent ]

pedal power | 14 comments (14 topical)

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