# The Naked Scientists Forum

### Author Topic: Can a bike power a washing machine?  (Read 8628 times)

#### thedoc

• Sr. Member
• Posts: 511
• Thanked: 12 times
##### Can a bike power a washing machine?
« on: 03/08/2010 17:23:21 »
Alex Gadsden tells us about his pedal-powered washing machine - how it works and what it can do.
Read a transcript of the interview by clicking here

« Last Edit: 03/08/2010 17:23:21 by _system »

#### Jolly- Joliver

• Hero Member
• Posts: 584
##### Can a bike power a washing machine?
« Reply #1 on: 30/03/2011 01:28:43 »
They already do. Giros power lights as you ride(we can debate if that a machine ofcourse)

#### imatfaal

• Neilep Level Member
• Posts: 2787
• rouge moderator
##### Can a bike power a washing machine?
« Reply #2 on: 30/03/2011 12:46:39 »
They already do. Giros power lights as you ride(we can debate if that a machine ofcourse)

We can definitely debate if it is a "washing machine" per the question - and it's dynamos not giros.

#### Jolly- Joliver

• Hero Member
• Posts: 584
##### Can a bike power a washing machine?
« Reply #3 on: 30/03/2011 12:50:27 »
They already do. Giros power lights as you ride(we can debate if that a machine ofcourse)

We can definitely debate if it is a "washing machine" per the question - and it's dynamos not giros.

Good point.

#### syhprum

• Neilep Level Member
• Posts: 3813
• Thanked: 19 times
##### Can a bike power a washing machine?
« Reply #4 on: 30/03/2011 13:22:53 »
An energetic cyclist can maintain an output of about 200 Watts, enough for spinning and churning no doubt but heating would take a long time.

#### Jolly- Joliver

• Hero Member
• Posts: 584
##### Can a bike power a washing machine?
« Reply #5 on: 30/03/2011 14:06:18 »
An energetic cyclist can maintain an output of about 200 Watts, enough for spinning and churning no doubt but heating would take a long time.

I'm sure using pully systems, you could increase the number of dynamos and generate a greater amount of power.

A fixed bike with a double chain driving the frount and back wheels for example. It gets harder to start but if there was assistence at the begining for the rider maintianing that would be easier.

#### imatfaal

• Neilep Level Member
• Posts: 2787
• rouge moderator
##### Can a bike power a washing machine?
« Reply #6 on: 30/03/2011 15:49:22 »
No no no!  You cannot create extra energy by using pulley systems or levers.  You can give yourself a mechanical advantage using a lever or a pulley; but you can never generate more power or get more energy.  And if it gets easier you are, on the whole, putting less energy into the system and thus less can be extracted.

#### Jolly- Joliver

• Hero Member
• Posts: 584
##### Can a bike power a washing machine?
« Reply #7 on: 31/03/2011 07:35:56 »
No no no!  You cannot create extra energy by using pulley systems or levers.  You can give yourself a mechanical advantage using a lever or a pulley; but you can never generate more power or get more energy.  And if it gets easier you are, on the whole, putting less energy into the system and thus less can be extracted.

Just a minute, if I used a system of pullies to make it easier on my legs and turn bigger dynamos.

Power is comming from the person and that can vary.

#### rosy

• Neilep Level Member
• Posts: 1018
• Chemistry
##### Can a bike power a washing machine?
« Reply #8 on: 31/03/2011 10:01:30 »
Nope. Lower gearing can make it easier on your legs to turn a dynamo, but you'll only turn it ve-e-e-ery slowly, and the amount of power you generate depends on how fast you can turn it.
You can't increase the power out of your legs beyond a certain point. It's an "energy in is always less than energy out thing again". Do you own a pushbike? With gears? You can try it... if you change down a gear when going up hill, you don't have to work so hard to turn the wheels by one turn, but you don't go so far per turn either. It all balances out... and infact it's always less effort over all to use the highest gear you can (less frantic going-round-and-round per amount of useful effort).

#### imatfaal

• Neilep Level Member
• Posts: 2787
• rouge moderator
##### Can a bike power a washing machine?
« Reply #9 on: 31/03/2011 10:59:45 »
Rosy - dead right on the physics/thermodynamics, not so sure about the biomechanics.

Quote
and infact it's always less effort over all to use the highest gear you can (less frantic going-round-and-round per amount of useful effort)

The most efficient long period method of cycling is with a high(ish) cadence low(ish) effort - you can keep your legs turning over quite rapidly for long periods when the resistance is low

#### Jolly- Joliver

• Hero Member
• Posts: 584
##### Can a bike power a washing machine?
« Reply #10 on: 31/03/2011 13:42:21 »
Nope. Lower gearing can make it easier on your legs to turn a dynamo, but you'll only turn it ve-e-e-ery slowly, and the amount of power you generate depends on how fast you can turn it.
You can't increase the power out of your legs beyond a certain point. It's an "energy in is always less than energy out thing again". Do you own a pushbike? With gears? You can try it... if you change down a gear when going up hill, you don't have to work so hard to turn the wheels by one turn, but you don't go so far per turn either. It all balances out... and infact it's always less effort over all to use the highest gear you can (less frantic going-round-and-round per amount of useful effort).

It's magnets turing around wires. There are ways to do that, that take less energy, to achieve a a good spin.

#### rosy

• Neilep Level Member
• Posts: 1018
• Chemistry
##### Can a bike power a washing machine?
« Reply #11 on: 31/03/2011 14:29:34 »
Quote
There are ways to do that, that take less energy, to achieve a a good spin.

Up to a certain limit.

You cannot get out more energy than you can put in. And the peak energy that you can put in is less than the peak energy required by a washing machine (certainly if you're trying to heat the water too). If you could charge a battery and then use the stored energy to run the machine, then you could certainly do it.

#### rosy

• Neilep Level Member
• Posts: 1018
• Chemistry
##### Can a bike power a washing machine?
« Reply #12 on: 31/03/2011 14:40:22 »
Quote
The most efficient long period method of cycling is with a high(ish) cadence low(ish) effort - you can keep your legs turning over quite rapidly for long periods when the resistance is low

Really? I'm prepared to believe that in principle, but it doesn't accord with my experience in practice (tho' perhaps that's because my bike's not geared excessively high, and I live in Cambridge, which is dead flat, so mostly I reach top gear a few yards out of the traffic light and stop there... and I'm not generally trying for very high speeds, because in town that would be basically suicidal).

Cycling on the flat, of course, once you're up to speed you're only working against friction and air resistance, and air resistance gets worse in a non-linear way (I think?) if you go faster, so distance-for-distance I'd expect you'd use less energy going a bit slower? Up hill (well, up-the-side-of-the-railway-bridge), though, (it feels like) it's less effort to maintain a higher gear, go faster, and get to the top sooner, than to change down and welly the pedals, provided I'm going fast enough initially to get embarked on the slope and keep up the momentum.

But I've not really thought about any of this in depth..

#### Jolly- Joliver

• Hero Member
• Posts: 584
##### Can a bike power a washing machine?
« Reply #13 on: 31/03/2011 15:37:04 »
Quote
There are ways to do that, that take less energy, to achieve a a good spin.

Up to a certain limit.

You cannot get out more energy than you can put in. And the peak energy that you can put in is less than the peak energy required by a washing machine (certainly if you're trying to heat the water too). If you could charge a battery and then use the stored energy to run the machine, then you could certainly do it.

Fine but how much energy is going in when someone peddles? I mean really. When you think about the energy of a person thinking about peddling, and then using all the different mussels they will to peddle.

It's easier to maintain a speed once your going, That's why I was suggesting a system to assit at the begging to get you going.

But just like with bike wheel, if the bike is upside down and you turn the peddles the wheel will carry on when you stop until friction causes it to stop completely.

A Dynamo could work under the same principle, the energy in one peddle could if it was designed well, cause it to spin many times.

There are many ways to design a dynamo, if you placed the heavier materials on the outside and they were fixed and the lighter wires on a light tube spin inside, the effort to turn that would be a lot less than trying to spin the heavy magnets.

Just suggesting bracking down the process and then designing a dynamo that spins more efficiently, off a peddle bike, pullys, combining a few dyanmos, assistence to start peddling, I think you could potencially get a good amount of power from it.

#### peppercorn

• Neilep Level Member
• Posts: 1466
##### Can a bike power a washing machine?
« Reply #14 on: 31/03/2011 16:50:06 »
It's easier to maintain a speed once your going, That's why I was suggesting a system to assist at the begging to get you going.

I believe most bikes come with gears

I assume the human body, like any machine, has optimum operating conditions (for cycling, a rate of peddling at a certain load; also dependent on fitness, etc).  A cycle/generator that is optimised for this combination of revs and load (torque) is going to give the most efficient power possible.
Ultimately, though, there will have to be other reasons to use pedal power for electric generation.  These could be improving/conserving the fitness of the individual, an 'emergency' power source or an educational exercise.

#### Pumblechook

• Hero Member
• Posts: 569
##### Can a bike power a washing machine?
« Reply #15 on: 31/03/2011 16:57:47 »
You may be able to spin the drum but for how long?  It would not be possible to heat the water.  Most modern machines are cold fill.  Most of the energy is used heating the water.

#### Jolly- Joliver

• Hero Member
• Posts: 584
##### Can a bike power a washing machine?
« Reply #16 on: 31/03/2011 17:21:13 »
It's easier to maintain a speed once your going, That's why I was suggesting a system to assist at the begging to get you going.

I believe most bikes come with gears

I was making the point that if you connected up a few dynamos it would be a hassel to get going, so some assitence might be needed, gears or not.

#### Bored chemist

• Neilep Level Member
• Posts: 8648
• Thanked: 42 times
##### Can a bike power a washing machine?
« Reply #17 on: 31/03/2011 20:00:47 »
The most efficient way to heat the water would be to turn the drum, so the water tumbles inside it and is heated by work done against viscosity.

The issue of gearing is related to the issue of impedance matching. You can do worse than the optimum, but you can't do better.

#### peppercorn

• Neilep Level Member
• Posts: 1466
##### Can a bike power a washing machine?
« Reply #18 on: 31/03/2011 21:03:51 »
I believe most bikes come with gears
I was making the point that if you connected up a few dynamos it would be a hassel to get going, so some assitence might be needed, gears or not.

But I was making the point that that's what gears do! - The resistance to getting moving would be lessened by having gears - just like 'getting moving' riding up a really steep hill.  ..... Alternatively you can use a power-controller to change the load on the motor to suit to power provided.

The most efficient way to heat the water would be to turn the drum, so the water tumbles inside it and is heated by work done against viscosity.
But we all know that efficient is not the same as useful, eh?
Efficient and useful! - now you've got something there!

The issue of gearing is related to the issue of impedance matching.

'Impedance matching' now that's the term I was looking for! It reminds me of my electronics course for some reason...
« Last Edit: 31/03/2011 21:10:06 by peppercorn »

#### Geezer

• Neilep Level Member
• Posts: 8328
• "Vive la résistance!"
##### Can a bike power a washing machine?
« Reply #19 on: 31/03/2011 21:45:57 »
Quote
The most efficient long period method of cycling is with a high(ish) cadence low(ish) effort - you can keep your legs turning over quite rapidly for long periods when the resistance is low

Really? I'm prepared to believe that in principle, but it doesn't accord with my experience in practice (tho' perhaps that's because my bike's not geared excessively high, and I live in Cambridge, which is dead flat, so mostly I reach top gear a few yards out of the traffic light and stop there... and I'm not generally trying for very high speeds, because in town that would be basically suicidal).

Cycling on the flat, of course, once you're up to speed you're only working against friction and air resistance, and air resistance gets worse in a non-linear way (I think?) if you go faster, so distance-for-distance I'd expect you'd use less energy going a bit slower? Up hill (well, up-the-side-of-the-railway-bridge), though, (it feels like) it's less effort to maintain a higher gear, go faster, and get to the top sooner, than to change down and welly the pedals, provided I'm going fast enough initially to get embarked on the slope and keep up the momentum.

But I've not really thought about any of this in depth..

Ahem! Matt is right.

If you want to go as fast as possible, you need to develop maximum power. Power is the product of torque (the pressure you exert on the pedals times the length of the crank) times the rotational speed of the cranks.

You can generate a lot of torque (particularly if you stand on the pedals), but if the cranks are only rotating slowly, you are producing hardly any power.
« Last Edit: 01/04/2011 05:09:36 by Geezer »

#### maria do carmo nascimento

• Guest
##### None
« Reply #20 on: 11/12/2014 22:31:24 »
hi alex I always think about that but I coudn't do it because I'm not good in engineering  I'm a physian in Brazil I congratulate you for this invention . Maria do Carmo Nascimento 11th December 2014

#### The Naked Scientists Forum

##### None
« Reply #20 on: 11/12/2014 22:31:24 »